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LU-5274 llite: fix ll_statahead_thread() problems on failure
[fs/lustre-release.git] / lustre / llite / statahead.c
index 21846cf..cc290aa 100644 (file)
@@ -1,6 +1,4 @@
-/* -*- mode: c; c-basic-offset: 8; indent-tabs-mode: nil; -*-
- * vim:expandtab:shiftwidth=8:tabstop=8:
- *
+/*
  * GPL HEADER START
  *
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  * GPL HEADER END
  */
 /*
- * Copyright  2008 Sun Microsystems, Inc. All rights reserved
+ * Copyright (c) 2008, 2010, Oracle and/or its affiliates. All rights reserved.
  * Use is subject to license terms.
+ *
+ * Copyright (c) 2011, 2013, Intel Corporation.
  */
 /*
  * This file is part of Lustre, http://www.lustre.org/
@@ -37,7 +37,6 @@
 #include <linux/fs.h>
 #include <linux/sched.h>
 #include <linux/mm.h>
-#include <linux/smp_lock.h>
 #include <linux/highmem.h>
 #include <linux/pagemap.h>
 
 #include <obd_support.h>
 #include <lustre_lite.h>
 #include <lustre_dlm.h>
-#include <linux/lustre_version.h>
 #include "llite_internal.h"
 
-struct ll_sai_entry {
-        cfs_list_t              se_list;
-        unsigned int            se_index;
-        int                     se_stat;
-        struct ptlrpc_request  *se_req;
-        struct md_enqueue_info *se_minfo;
-};
-
-enum {
-        SA_ENTRY_UNSTATED = 0,
-        SA_ENTRY_STATED
+#define SA_OMITTED_ENTRY_MAX 8ULL
+
+typedef enum {
+        /** negative values are for error cases */
+        SA_ENTRY_INIT = 0,      /** init entry */
+        SA_ENTRY_SUCC = 1,      /** stat succeed */
+        SA_ENTRY_INVA = 2,      /** invalid entry */
+        SA_ENTRY_DEST = 3,      /** entry to be destroyed */
+} se_stat_t;
+
+struct ll_sa_entry {
+       /* link into sai->sai_entries */
+       struct list_head        se_link;
+       /* link into sai->sai_entries_{received,stated} */
+       struct list_head        se_list;
+       /* link into sai hash table locally */
+       struct list_head        se_hash;
+       /* entry reference count */
+       atomic_t                se_refcount;
+       /* entry index in the sai */
+       __u64                   se_index;
+       /* low layer ldlm lock handle */
+       __u64                   se_handle;
+       /* entry status */
+       se_stat_t               se_stat;
+       /* entry size, contains name */
+       int                     se_size;
+       /* pointer to async getattr enqueue info */
+       struct md_enqueue_info *se_minfo;
+       /* pointer to the async getattr request */
+       struct ptlrpc_request  *se_req;
+       /* pointer to the target inode */
+       struct inode           *se_inode;
+       /* entry name */
+       struct qstr             se_qstr;
 };
 
 static unsigned int sai_generation = 0;
-static cfs_spinlock_t sai_generation_lock = CFS_SPIN_LOCK_UNLOCKED;
+static DEFINE_SPINLOCK(sai_generation_lock);
 
-/**
- * Check whether first entry was stated already or not.
- * No need to hold lli_lock, for:
- * (1) it is me that remove entry from the list
- * (2) the statahead thread only add new entry to the list
+static inline int ll_sa_entry_unhashed(struct ll_sa_entry *entry)
+{
+       return list_empty(&entry->se_hash);
+}
+
+/*
+ * The entry only can be released by the caller, it is necessary to hold lock.
  */
-static int ll_sai_entry_stated(struct ll_statahead_info *sai)
+static inline int ll_sa_entry_stated(struct ll_sa_entry *entry)
 {
-        struct ll_sai_entry  *entry;
-        int                   rc = 0;
-
-        if (!cfs_list_empty(&sai->sai_entries_stated)) {
-                entry = cfs_list_entry(sai->sai_entries_stated.next,
-                                       struct ll_sai_entry, se_list);
-                if (entry->se_index == sai->sai_index_next)
-                        rc = 1;
-        }
-        return rc;
+        smp_rmb();
+        return (entry->se_stat != SA_ENTRY_INIT);
 }
 
-static inline int sa_received_empty(struct ll_statahead_info *sai)
+static inline int ll_sa_entry_hash(int val)
+{
+        return val & LL_SA_CACHE_MASK;
+}
+
+/*
+ * Insert entry to hash SA table.
+ */
+static inline void
+ll_sa_entry_enhash(struct ll_statahead_info *sai, struct ll_sa_entry *entry)
+{
+       int i = ll_sa_entry_hash(entry->se_qstr.hash);
+
+       spin_lock(&sai->sai_cache_lock[i]);
+       list_add_tail(&entry->se_hash, &sai->sai_cache[i]);
+       spin_unlock(&sai->sai_cache_lock[i]);
+}
+
+/*
+ * Remove entry from SA table.
+ */
+static inline void
+ll_sa_entry_unhash(struct ll_statahead_info *sai, struct ll_sa_entry *entry)
+{
+       int i = ll_sa_entry_hash(entry->se_qstr.hash);
+
+       spin_lock(&sai->sai_cache_lock[i]);
+       list_del_init(&entry->se_hash);
+       spin_unlock(&sai->sai_cache_lock[i]);
+}
+
+static inline int agl_should_run(struct ll_statahead_info *sai,
+                                 struct inode *inode)
+{
+       return (inode != NULL && S_ISREG(inode->i_mode) && sai->sai_agl_valid);
+}
+
+static inline struct ll_sa_entry *
+sa_first_received_entry(struct ll_statahead_info *sai)
 {
-        return cfs_list_empty(&sai->sai_entries_received);
+       return list_entry(sai->sai_entries_received.next,
+                         struct ll_sa_entry, se_list);
 }
 
-static inline int sa_not_full(struct ll_statahead_info *sai)
+static inline struct ll_inode_info *
+agl_first_entry(struct ll_statahead_info *sai)
 {
-        return (sai->sai_index < sai->sai_hit + sai->sai_miss + sai->sai_max);
+       return list_entry(sai->sai_entries_agl.next,
+                         struct ll_inode_info, lli_agl_list);
 }
 
-static inline int sa_is_running(struct ll_statahead_info *sai)
+static inline int sa_sent_full(struct ll_statahead_info *sai)
 {
-        return !!(sai->sai_thread.t_flags & SVC_RUNNING);
+       return atomic_read(&sai->sai_cache_count) >= sai->sai_max;
 }
 
-static inline int sa_is_stopping(struct ll_statahead_info *sai)
+static inline int sa_received_empty(struct ll_statahead_info *sai)
 {
-        return !!(sai->sai_thread.t_flags & SVC_STOPPING);
+       return list_empty(&sai->sai_entries_received);
 }
 
-static inline int sa_is_stopped(struct ll_statahead_info *sai)
+static inline int agl_list_empty(struct ll_statahead_info *sai)
 {
-        return !!(sai->sai_thread.t_flags & SVC_STOPPED);
+       return list_empty(&sai->sai_entries_agl);
 }
 
 /**
  * (1) hit ratio less than 80%
  * or
  * (2) consecutive miss more than 8
+ * then means low hit.
  */
 static inline int sa_low_hit(struct ll_statahead_info *sai)
 {
@@ -121,412 +179,603 @@ static inline int sa_low_hit(struct ll_statahead_info *sai)
                 (sai->sai_consecutive_miss > 8));
 }
 
-/**
- * process the deleted entry's member and free the entry.
- * (1) release intent
- * (2) free md_enqueue_info
- * (3) drop dentry's ref count
- * (4) release request's ref count
+/*
+ * If the given index is behind of statahead window more than
+ * SA_OMITTED_ENTRY_MAX, then it is old.
  */
-static void ll_sai_entry_cleanup(struct ll_sai_entry *entry, int free)
+static inline int is_omitted_entry(struct ll_statahead_info *sai, __u64 index)
 {
-        struct md_enqueue_info *minfo = entry->se_minfo;
-        struct ptlrpc_request  *req = entry->se_req;
+        return ((__u64)sai->sai_max + index + SA_OMITTED_ENTRY_MAX <
+                 sai->sai_index);
+}
+
+/*
+ * Insert it into sai_entries tail when init.
+ */
+static struct ll_sa_entry *
+ll_sa_entry_alloc(struct ll_statahead_info *sai, __u64 index,
+                  const char *name, int len)
+{
+        struct ll_inode_info *lli;
+        struct ll_sa_entry   *entry;
+        int                   entry_size;
+        char                 *dname;
         ENTRY;
 
+        entry_size = sizeof(struct ll_sa_entry) + (len & ~3) + 4;
+        OBD_ALLOC(entry, entry_size);
+        if (unlikely(entry == NULL))
+                RETURN(ERR_PTR(-ENOMEM));
+
+       CDEBUG(D_READA, "alloc sa entry %.*s(%p) index "LPU64"\n",
+              len, name, entry, index);
+
+        entry->se_index = index;
+
+       /*
+        * Statahead entry reference rules:
+        *
+        * 1) When statahead entry is initialized, its reference is set as 2.
+        *    One reference is used by the directory scanner. When the scanner
+        *    searches the statahead cache for the given name, it can perform
+        *    lockless hash lookup (only the scanner can remove entry from hash
+        *    list), and once found, it needn't to call "atomic_inc()" for the
+        *    entry reference. So the performance is improved. After using the
+        *    statahead entry, the scanner will call "atomic_dec()" to drop the
+        *    reference held when initialization. If it is the last reference,
+        *    the statahead entry will be freed.
+        *
+        * 2) All other threads, including statahead thread and ptlrpcd thread,
+        *    when they process the statahead entry, the reference for target
+        *    should be held to guarantee the entry will not be released by the
+        *    directory scanner. After processing the entry, these threads will
+        *    drop the entry reference. If it is the last reference, the entry
+        *    will be freed.
+        *
+        *    The second reference when initializes the statahead entry is used
+        *    by the statahead thread, following the rule 2).
+        */
+       atomic_set(&entry->se_refcount, 2);
+       entry->se_stat = SA_ENTRY_INIT;
+       entry->se_size = entry_size;
+       dname = (char *)entry + sizeof(struct ll_sa_entry);
+       memcpy(dname, name, len);
+       dname[len] = 0;
+       entry->se_qstr.hash = full_name_hash(name, len);
+       entry->se_qstr.len = len;
+       entry->se_qstr.name = dname;
+
+       lli = ll_i2info(sai->sai_inode);
+       spin_lock(&lli->lli_sa_lock);
+       list_add_tail(&entry->se_link, &sai->sai_entries);
+       INIT_LIST_HEAD(&entry->se_list);
+       ll_sa_entry_enhash(sai, entry);
+       spin_unlock(&lli->lli_sa_lock);
+
+       atomic_inc(&sai->sai_cache_count);
+
+       RETURN(entry);
+}
+
+/*
+ * Used by the directory scanner to search entry with name.
+ *
+ * Only the caller can remove the entry from hash, so it is unnecessary to hold
+ * hash lock. It is caller's duty to release the init refcount on the entry, so
+ * it is also unnecessary to increase refcount on the entry.
+ */
+static struct ll_sa_entry *
+ll_sa_entry_get_byname(struct ll_statahead_info *sai, const struct qstr *qstr)
+{
+        struct ll_sa_entry *entry;
+        int i = ll_sa_entry_hash(qstr->hash);
+
+       list_for_each_entry(entry, &sai->sai_cache[i], se_hash) {
+                if (entry->se_qstr.hash == qstr->hash &&
+                    entry->se_qstr.len == qstr->len &&
+                    memcmp(entry->se_qstr.name, qstr->name, qstr->len) == 0)
+                        return entry;
+        }
+        return NULL;
+}
+
+/*
+ * Used by the async getattr request callback to find entry with index.
+ *
+ * Inside lli_sa_lock to prevent others to change the list during the search.
+ * It needs to increase entry refcount before returning to guarantee that the
+ * entry cannot be freed by others.
+ */
+static struct ll_sa_entry *
+ll_sa_entry_get_byindex(struct ll_statahead_info *sai, __u64 index)
+{
+       struct ll_sa_entry *entry;
+
+       list_for_each_entry(entry, &sai->sai_entries, se_link) {
+               if (entry->se_index == index) {
+                       LASSERT(atomic_read(&entry->se_refcount) > 0);
+                       atomic_inc(&entry->se_refcount);
+                       return entry;
+                }
+               if (entry->se_index > index)
+                       break;
+       }
+       return NULL;
+}
+
+static void ll_sa_entry_cleanup(struct ll_statahead_info *sai,
+                                 struct ll_sa_entry *entry)
+{
+        struct md_enqueue_info *minfo = entry->se_minfo;
+        struct ptlrpc_request  *req   = entry->se_req;
+
         if (minfo) {
                 entry->se_minfo = NULL;
                 ll_intent_release(&minfo->mi_it);
-                dput(minfo->mi_dentry);
                 iput(minfo->mi_dir);
                 OBD_FREE_PTR(minfo);
         }
+
         if (req) {
                 entry->se_req = NULL;
                 ptlrpc_req_finished(req);
         }
-        if (free) {
-                LASSERT(cfs_list_empty(&entry->se_list));
-                OBD_FREE_PTR(entry);
-        }
-
-        EXIT;
-}
-
-static struct ll_statahead_info *ll_sai_alloc(void)
-{
-        struct ll_statahead_info *sai;
-
-        OBD_ALLOC_PTR(sai);
-        if (!sai)
-                return NULL;
-
-        cfs_spin_lock(&sai_generation_lock);
-        sai->sai_generation = ++sai_generation;
-        if (unlikely(sai_generation == 0))
-                sai->sai_generation = ++sai_generation;
-        cfs_spin_unlock(&sai_generation_lock);
-        cfs_atomic_set(&sai->sai_refcount, 1);
-        sai->sai_max = LL_SA_RPC_MIN;
-        cfs_waitq_init(&sai->sai_waitq);
-        cfs_waitq_init(&sai->sai_thread.t_ctl_waitq);
-        CFS_INIT_LIST_HEAD(&sai->sai_entries_sent);
-        CFS_INIT_LIST_HEAD(&sai->sai_entries_received);
-        CFS_INIT_LIST_HEAD(&sai->sai_entries_stated);
-        return sai;
 }
 
-static inline
-struct ll_statahead_info *ll_sai_get(struct ll_statahead_info *sai)
+static void ll_sa_entry_put(struct ll_statahead_info *sai,
+                             struct ll_sa_entry *entry)
 {
-        LASSERT(sai);
-        cfs_atomic_inc(&sai->sai_refcount);
-        return sai;
+       if (atomic_dec_and_test(&entry->se_refcount)) {
+               CDEBUG(D_READA, "free sa entry %.*s(%p) index "LPU64"\n",
+                      entry->se_qstr.len, entry->se_qstr.name, entry,
+                      entry->se_index);
+
+               LASSERT(list_empty(&entry->se_link));
+               LASSERT(list_empty(&entry->se_list));
+               LASSERT(ll_sa_entry_unhashed(entry));
+
+               ll_sa_entry_cleanup(sai, entry);
+               if (entry->se_inode)
+                       iput(entry->se_inode);
+
+               OBD_FREE(entry, entry->se_size);
+               atomic_dec(&sai->sai_cache_count);
+       }
 }
 
-static void ll_sai_put(struct ll_statahead_info *sai)
+static inline void
+do_sa_entry_fini(struct ll_statahead_info *sai, struct ll_sa_entry *entry)
 {
-        struct inode         *inode = sai->sai_inode;
-        struct ll_inode_info *lli;
-        ENTRY;
+       struct ll_inode_info *lli = ll_i2info(sai->sai_inode);
 
-        LASSERT(inode != NULL);
-        lli = ll_i2info(inode);
-        LASSERT(lli->lli_sai == sai);
+       LASSERT(!ll_sa_entry_unhashed(entry));
+       LASSERT(!list_empty(&entry->se_link));
 
-        if (cfs_atomic_dec_and_test(&sai->sai_refcount)) {
-                struct ll_sai_entry *entry, *next;
+       ll_sa_entry_unhash(sai, entry);
 
-                cfs_spin_lock(&lli->lli_lock);
-                if (unlikely(cfs_atomic_read(&sai->sai_refcount) > 0)) {
-                        /* It is race case, the interpret callback just hold
-                         * a reference count */
-                        cfs_spin_unlock(&lli->lli_lock);
-                        EXIT;
-                        return;
-                }
+       spin_lock(&lli->lli_sa_lock);
+       entry->se_stat = SA_ENTRY_DEST;
+       list_del_init(&entry->se_link);
+       if (likely(!list_empty(&entry->se_list)))
+               list_del_init(&entry->se_list);
+       spin_unlock(&lli->lli_sa_lock);
 
-                LASSERT(lli->lli_opendir_key == NULL);
-                lli->lli_sai = NULL;
-                lli->lli_opendir_pid = 0;
-                cfs_spin_unlock(&lli->lli_lock);
+       ll_sa_entry_put(sai, entry);
+}
 
-                LASSERT(sa_is_stopped(sai));
+/*
+ * Delete it from sai_entries_stated list when fini.
+ */
+static void
+ll_sa_entry_fini(struct ll_statahead_info *sai, struct ll_sa_entry *entry)
+{
+       struct ll_sa_entry *pos, *next;
 
-                if (sai->sai_sent > sai->sai_replied)
-                        CDEBUG(D_READA,"statahead for dir "DFID" does not "
-                              "finish: [sent:%u] [replied:%u]\n",
-                              PFID(&lli->lli_fid),
-                              sai->sai_sent, sai->sai_replied);
+       if (entry)
+               do_sa_entry_fini(sai, entry);
 
-                cfs_list_for_each_entry_safe(entry, next,
-                                             &sai->sai_entries_sent, se_list) {
-                        cfs_list_del_init(&entry->se_list);
-                        ll_sai_entry_cleanup(entry, 1);
-                }
-                cfs_list_for_each_entry_safe(entry, next,
-                                             &sai->sai_entries_received,
-                                             se_list) {
-                        cfs_list_del_init(&entry->se_list);
-                        ll_sai_entry_cleanup(entry, 1);
-                }
-                cfs_list_for_each_entry_safe(entry, next,
-                                             &sai->sai_entries_stated,
-                                             se_list) {
-                        cfs_list_del_init(&entry->se_list);
-                        ll_sai_entry_cleanup(entry, 1);
-                }
-                iput(inode);
-                OBD_FREE_PTR(sai);
-        }
-        EXIT;
+       /* drop old entry, only 'scanner' process does this, no need to lock */
+       list_for_each_entry_safe(pos, next, &sai->sai_entries, se_link) {
+               if (!is_omitted_entry(sai, pos->se_index))
+                       break;
+               do_sa_entry_fini(sai, pos);
+       }
 }
 
-/**
- * insert it into sai_entries_sent tail when init.
+/*
+ * Inside lli_sa_lock.
  */
-static struct ll_sai_entry *
-ll_sai_entry_init(struct ll_statahead_info *sai, unsigned int index)
+static void
+do_sa_entry_to_stated(struct ll_statahead_info *sai,
+                     struct ll_sa_entry *entry, se_stat_t stat)
 {
-        struct ll_inode_info *lli = ll_i2info(sai->sai_inode);
-        struct ll_sai_entry  *entry;
-        ENTRY;
-
-        OBD_ALLOC_PTR(entry);
-        if (entry == NULL)
-                RETURN(ERR_PTR(-ENOMEM));
+       struct ll_sa_entry *se;
+       struct list_head   *pos = &sai->sai_entries_stated;
 
-        CDEBUG(D_READA, "alloc sai entry %p index %u\n",
-               entry, index);
-        entry->se_index = index;
-        entry->se_stat  = SA_ENTRY_UNSTATED;
+       if (!list_empty(&entry->se_list))
+               list_del_init(&entry->se_list);
 
-        cfs_spin_lock(&lli->lli_lock);
-        cfs_list_add_tail(&entry->se_list, &sai->sai_entries_sent);
-        cfs_spin_unlock(&lli->lli_lock);
+       list_for_each_entry_reverse(se, &sai->sai_entries_stated, se_list) {
+               if (se->se_index < entry->se_index) {
+                       pos = &se->se_list;
+                       break;
+               }
+       }
 
-        RETURN(entry);
+       list_add(&entry->se_list, pos);
+       entry->se_stat = stat;
 }
 
-/**
- * delete it from sai_entries_stated head when fini, it need not
- * to process entry's member.
+/*
+ * Move entry to sai_entries_stated and sort with the index.
+ * \retval 1    -- entry to be destroyed.
+ * \retval 0    -- entry is inserted into stated list.
  */
-static void ll_sai_entry_fini(struct ll_statahead_info *sai)
+static int
+ll_sa_entry_to_stated(struct ll_statahead_info *sai,
+                     struct ll_sa_entry *entry, se_stat_t stat)
 {
-        struct ll_inode_info *lli = ll_i2info(sai->sai_inode);
-        struct ll_sai_entry  *entry;
-        ENTRY;
+       struct ll_inode_info *lli = ll_i2info(sai->sai_inode);
+       int                   ret = 1;
 
-        cfs_spin_lock(&lli->lli_lock);
-        sai->sai_index_next++;
-        if (likely(!cfs_list_empty(&sai->sai_entries_stated))) {
-                entry = cfs_list_entry(sai->sai_entries_stated.next,
-                                       struct ll_sai_entry, se_list);
-                if (entry->se_index < sai->sai_index_next) {
-                        cfs_list_del(&entry->se_list);
-                        OBD_FREE_PTR(entry);
-                }
-        } else
-                LASSERT(sa_is_stopped(sai));
-        cfs_spin_unlock(&lli->lli_lock);
+       ll_sa_entry_cleanup(sai, entry);
 
-        EXIT;
+       spin_lock(&lli->lli_sa_lock);
+       if (likely(entry->se_stat != SA_ENTRY_DEST)) {
+               do_sa_entry_to_stated(sai, entry, stat);
+               ret = 0;
+       }
+       spin_unlock(&lli->lli_sa_lock);
+
+       return ret;
 }
 
-/**
- * inside lli_lock.
- * \retval NULL : can not find the entry in sai_entries_sent with the index
- * \retval entry: find the entry in sai_entries_sent with the index
+/*
+ * Insert inode into the list of sai_entries_agl.
  */
-static struct ll_sai_entry *
-ll_sai_entry_set(struct ll_statahead_info *sai, unsigned int index, int stat,
-                 struct ptlrpc_request *req, struct md_enqueue_info *minfo)
+static void ll_agl_add(struct ll_statahead_info *sai,
+                       struct inode *inode, int index)
 {
-        struct ll_sai_entry *entry;
-        ENTRY;
+       struct ll_inode_info *child  = ll_i2info(inode);
+       struct ll_inode_info *parent = ll_i2info(sai->sai_inode);
+       int                   added  = 0;
+
+       spin_lock(&child->lli_agl_lock);
+       if (child->lli_agl_index == 0) {
+               child->lli_agl_index = index;
+               spin_unlock(&child->lli_agl_lock);
+
+               LASSERT(list_empty(&child->lli_agl_list));
+
+               igrab(inode);
+               spin_lock(&parent->lli_agl_lock);
+               if (agl_list_empty(sai))
+                       added = 1;
+               list_add_tail(&child->lli_agl_list, &sai->sai_entries_agl);
+               spin_unlock(&parent->lli_agl_lock);
+       } else {
+               spin_unlock(&child->lli_agl_lock);
+       }
+
+       if (added > 0)
+               wake_up(&sai->sai_agl_thread.t_ctl_waitq);
+}
 
-        if (!cfs_list_empty(&sai->sai_entries_sent)) {
-                cfs_list_for_each_entry(entry, &sai->sai_entries_sent,
-                                        se_list) {
-                        if (entry->se_index == index) {
-                                entry->se_stat = stat;
-                                entry->se_req = ptlrpc_request_addref(req);
-                                entry->se_minfo = minfo;
-                                RETURN(entry);
-                        } else if (entry->se_index > index)
-                                RETURN(NULL);
-                }
-        }
-        RETURN(NULL);
+static struct ll_statahead_info *ll_sai_alloc(void)
+{
+       struct ll_statahead_info *sai;
+       int                       i;
+       ENTRY;
+
+       OBD_ALLOC_PTR(sai);
+       if (!sai)
+               RETURN(NULL);
+
+       atomic_set(&sai->sai_refcount, 1);
+
+       spin_lock(&sai_generation_lock);
+       sai->sai_generation = ++sai_generation;
+       if (unlikely(sai_generation == 0))
+               sai->sai_generation = ++sai_generation;
+       spin_unlock(&sai_generation_lock);
+
+       sai->sai_max = LL_SA_RPC_MIN;
+       sai->sai_index = 1;
+       init_waitqueue_head(&sai->sai_waitq);
+       init_waitqueue_head(&sai->sai_thread.t_ctl_waitq);
+       init_waitqueue_head(&sai->sai_agl_thread.t_ctl_waitq);
+
+       INIT_LIST_HEAD(&sai->sai_entries);
+       INIT_LIST_HEAD(&sai->sai_entries_received);
+       INIT_LIST_HEAD(&sai->sai_entries_stated);
+       INIT_LIST_HEAD(&sai->sai_entries_agl);
+
+       for (i = 0; i < LL_SA_CACHE_SIZE; i++) {
+               INIT_LIST_HEAD(&sai->sai_cache[i]);
+               spin_lock_init(&sai->sai_cache_lock[i]);
+       }
+       atomic_set(&sai->sai_cache_count, 0);
+
+       RETURN(sai);
 }
 
-/**
- * inside lli_lock.
- * Move entry to sai_entries_received and
- * insert it into sai_entries_received tail.
- */
-static inline void
-ll_sai_entry_to_received(struct ll_statahead_info *sai, struct ll_sai_entry *entry)
+static inline struct ll_statahead_info *
+ll_sai_get(struct ll_statahead_info *sai)
 {
-        if (!cfs_list_empty(&entry->se_list))
-                cfs_list_del_init(&entry->se_list);
-        cfs_list_add_tail(&entry->se_list, &sai->sai_entries_received);
+       atomic_inc(&sai->sai_refcount);
+       return sai;
 }
 
-/**
- * Move entry to sai_entries_stated and
- * sort with the index.
- */
-static int
-ll_sai_entry_to_stated(struct ll_statahead_info *sai, struct ll_sai_entry *entry)
+static void ll_sai_put(struct ll_statahead_info *sai)
 {
-        struct ll_inode_info *lli = ll_i2info(sai->sai_inode);
-        struct ll_sai_entry  *se;
-        ENTRY;
+       struct inode         *inode = sai->sai_inode;
+       struct ll_inode_info *lli   = ll_i2info(inode);
+       ENTRY;
+
+       if (atomic_dec_and_lock(&sai->sai_refcount, &lli->lli_sa_lock)) {
+               struct ll_sa_entry *entry, *next;
+
+               if (unlikely(atomic_read(&sai->sai_refcount) > 0)) {
+                       /* It is race case, the interpret callback just hold
+                        * a reference count */
+                       spin_unlock(&lli->lli_sa_lock);
+                       RETURN_EXIT;
+               }
+
+               LASSERT(lli->lli_opendir_key == NULL);
+               LASSERT(thread_is_stopped(&sai->sai_thread));
+               LASSERT(thread_is_stopped(&sai->sai_agl_thread));
+
+               lli->lli_sai = NULL;
+               lli->lli_opendir_pid = 0;
+               spin_unlock(&lli->lli_sa_lock);
+
+                if (sai->sai_sent > sai->sai_replied)
+                        CDEBUG(D_READA,"statahead for dir "DFID" does not "
+                              "finish: [sent:"LPU64"] [replied:"LPU64"]\n",
+                              PFID(&lli->lli_fid),
+                              sai->sai_sent, sai->sai_replied);
+
+               list_for_each_entry_safe(entry, next,
+                                        &sai->sai_entries, se_link)
+                       do_sa_entry_fini(sai, entry);
+
+               LASSERT(list_empty(&sai->sai_entries));
+               LASSERT(sa_received_empty(sai));
+               LASSERT(list_empty(&sai->sai_entries_stated));
+
+               LASSERT(atomic_read(&sai->sai_cache_count) == 0);
+               LASSERT(agl_list_empty(sai));
 
-        ll_sai_entry_cleanup(entry, 0);
+               iput(inode);
+               OBD_FREE_PTR(sai);
+       }
+
+       EXIT;
+}
+
+/* Do NOT forget to drop inode refcount when into sai_entries_agl. */
+static void ll_agl_trigger(struct inode *inode, struct ll_statahead_info *sai)
+{
+        struct ll_inode_info *lli   = ll_i2info(inode);
+        __u64                 index = lli->lli_agl_index;
+        int                   rc;
+        ENTRY;
 
-        cfs_spin_lock(&lli->lli_lock);
-        if (!cfs_list_empty(&entry->se_list))
-                cfs_list_del_init(&entry->se_list);
+       LASSERT(list_empty(&lli->lli_agl_list));
 
-        if (unlikely(entry->se_index < sai->sai_index_next)) {
-                cfs_spin_unlock(&lli->lli_lock);
-                OBD_FREE_PTR(entry);
-                RETURN(0);
+        /* AGL maybe fall behind statahead with one entry */
+        if (is_omitted_entry(sai, index + 1)) {
+                lli->lli_agl_index = 0;
+                iput(inode);
+                RETURN_EXIT;
         }
 
-        cfs_list_for_each_entry_reverse(se, &sai->sai_entries_stated, se_list) {
-                if (se->se_index < entry->se_index) {
-                        cfs_list_add(&entry->se_list, &se->se_list);
-                        cfs_spin_unlock(&lli->lli_lock);
-                        RETURN(1);
-                }
+        /* Someone is in glimpse (sync or async), do nothing. */
+       rc = down_write_trylock(&lli->lli_glimpse_sem);
+        if (rc == 0) {
+                lli->lli_agl_index = 0;
+                iput(inode);
+                RETURN_EXIT;
         }
 
         /*
-         * I am the first entry.
+         * Someone triggered glimpse within 1 sec before.
+         * 1) The former glimpse succeeded with glimpse lock granted by OST, and
+         *    if the lock is still cached on client, AGL needs to do nothing. If
+         *    it is cancelled by other client, AGL maybe cannot obtaion new lock
+         *    for no glimpse callback triggered by AGL.
+         * 2) The former glimpse succeeded, but OST did not grant glimpse lock.
+         *    Under such case, it is quite possible that the OST will not grant
+         *    glimpse lock for AGL also.
+         * 3) The former glimpse failed, compared with other two cases, it is
+         *    relative rare. AGL can ignore such case, and it will not muchly
+         *    affect the performance.
          */
-        cfs_list_add(&entry->se_list, &sai->sai_entries_stated);
-        cfs_spin_unlock(&lli->lli_lock);
-        RETURN(1);
+        if (lli->lli_glimpse_time != 0 &&
+            cfs_time_before(cfs_time_shift(-1), lli->lli_glimpse_time)) {
+               up_write(&lli->lli_glimpse_sem);
+                lli->lli_agl_index = 0;
+                iput(inode);
+                RETURN_EXIT;
+        }
+
+        CDEBUG(D_READA, "Handling (init) async glimpse: inode = "
+               DFID", idx = "LPU64"\n", PFID(&lli->lli_fid), index);
+
+        cl_agl(inode);
+        lli->lli_agl_index = 0;
+        lli->lli_glimpse_time = cfs_time_current();
+       up_write(&lli->lli_glimpse_sem);
+
+        CDEBUG(D_READA, "Handled (init) async glimpse: inode= "
+               DFID", idx = "LPU64", rc = %d\n",
+               PFID(&lli->lli_fid), index, rc);
+
+        iput(inode);
+
+        EXIT;
 }
 
-/**
- * finish lookup/revalidate.
- */
-static int do_statahead_interpret(struct ll_statahead_info *sai)
+static void ll_post_statahead(struct ll_statahead_info *sai)
 {
-        struct ll_inode_info   *lli = ll_i2info(sai->sai_inode);
-        struct ll_sai_entry    *entry;
-        struct ptlrpc_request  *req;
+        struct inode           *dir   = sai->sai_inode;
+        struct inode           *child;
+        struct ll_inode_info   *lli   = ll_i2info(dir);
+        struct ll_sa_entry     *entry;
         struct md_enqueue_info *minfo;
         struct lookup_intent   *it;
-        struct dentry          *dentry;
-        int                     rc = 0;
+        struct ptlrpc_request  *req;
         struct mdt_body        *body;
+        int                     rc    = 0;
         ENTRY;
 
-        cfs_spin_lock(&lli->lli_lock);
-        LASSERT(!sa_received_empty(sai));
-        entry = cfs_list_entry(sai->sai_entries_received.next,
-                               struct ll_sai_entry, se_list);
-        cfs_list_del_init(&entry->se_list);
-        cfs_spin_unlock(&lli->lli_lock);
-
-        if (unlikely(entry->se_index < sai->sai_index_next)) {
-                CWARN("Found stale entry: [index %u] [next %u]\n",
-                      entry->se_index, sai->sai_index_next);
-                ll_sai_entry_cleanup(entry, 1);
-                RETURN(0);
-        }
+       spin_lock(&lli->lli_sa_lock);
+       if (unlikely(sa_received_empty(sai))) {
+               spin_unlock(&lli->lli_sa_lock);
+               RETURN_EXIT;
+       }
+       entry = sa_first_received_entry(sai);
+       atomic_inc(&entry->se_refcount);
+       list_del_init(&entry->se_list);
+       spin_unlock(&lli->lli_sa_lock);
 
-        if (entry->se_stat != SA_ENTRY_STATED)
-                GOTO(out, rc = entry->se_stat);
+        LASSERT(entry->se_handle != 0);
 
-        req = entry->se_req;
         minfo = entry->se_minfo;
         it = &minfo->mi_it;
-        dentry = minfo->mi_dentry;
-
+        req = entry->se_req;
         body = req_capsule_server_get(&req->rq_pill, &RMF_MDT_BODY);
         if (body == NULL)
                 GOTO(out, rc = -EFAULT);
 
-        if (dentry->d_inode == NULL) {
+        child = entry->se_inode;
+        if (child == NULL) {
                 /*
                  * lookup.
                  */
-                struct dentry    *save = dentry;
-                struct it_cb_data icbd = {
-                        .icbd_parent   = minfo->mi_dir,
-                        .icbd_childp   = &dentry
-                };
-
                 LASSERT(fid_is_zero(&minfo->mi_data.op_fid2));
 
-                /*
-                 * XXX: No fid in reply, this is probaly cross-ref case.
-                 * SA can't handle it yet.
-                 */
-                if (body->valid & OBD_MD_MDS)
-                        GOTO(out, rc = -EAGAIN);
-
-                rc = ll_lookup_it_finish(req, it, &icbd);
-                if (!rc)
-                        /*
-                         * Here dentry->d_inode might be NULL,
-                         * because the entry may have been removed before
-                         * we start doing stat ahead.
-                         */
-                        ll_lookup_finish_locks(it, dentry);
-
-                if (dentry != save) {
-                        minfo->mi_dentry = dentry;
-                        dput(save);
-                }
-        } else {
-                /*
-                 * revalidate.
-                 */
-                if (!lu_fid_eq(&minfo->mi_data.op_fid2, &body->fid1)) {
-                        ll_unhash_aliases(dentry->d_inode);
-                        GOTO(out, rc = -EAGAIN);
+                /* XXX: No fid in reply, this is probaly cross-ref case.
+                 * SA can't handle it yet. */
+               if (body->mbo_valid & OBD_MD_MDS)
+                       GOTO(out, rc = -EAGAIN);
+       } else {
+               /*
+                * revalidate.
+                */
+               /* unlinked and re-created with the same name */
+               if (unlikely(!lu_fid_eq(&minfo->mi_data.op_fid2,
+                                       &body->mbo_fid1))) {
+                        entry->se_inode = NULL;
+                        iput(child);
+                        child = NULL;
                 }
+        }
 
-                rc = ll_revalidate_it_finish(req, it, dentry);
-                if (rc) {
-                        ll_unhash_aliases(dentry->d_inode);
-                        GOTO(out, rc);
-                }
+        it->d.lustre.it_lock_handle = entry->se_handle;
+       rc = md_revalidate_lock(ll_i2mdexp(dir), it, ll_inode2fid(dir), NULL);
+        if (rc != 1)
+                GOTO(out, rc = -EAGAIN);
+
+        rc = ll_prep_inode(&child, req, dir->i_sb, it);
+        if (rc)
+                GOTO(out, rc);
+
+       CDEBUG(D_DLMTRACE, "%s: setting l_data to inode "DFID"(%p)\n",
+              ll_get_fsname(child->i_sb, NULL, 0),
+              PFID(ll_inode2fid(child)), child);
+        ll_set_lock_data(ll_i2sbi(dir)->ll_md_exp, child, it, NULL);
+
+        entry->se_inode = child;
+
+        if (agl_should_run(sai, child))
+                ll_agl_add(sai, child, entry->se_index);
 
-                cfs_spin_lock(&ll_lookup_lock);
-                spin_lock(&dcache_lock);
-                lock_dentry(dentry);
-                __d_drop(dentry);
-                dentry->d_flags &= ~DCACHE_LUSTRE_INVALID;
-                unlock_dentry(dentry);
-                d_rehash_cond(dentry, 0);
-                spin_unlock(&dcache_lock);
-                cfs_spin_unlock(&ll_lookup_lock);
-
-                ll_lookup_finish_locks(it, dentry);
-        }
         EXIT;
 
 out:
-        if (likely(ll_sai_entry_to_stated(sai, entry)))
-                cfs_waitq_signal(&sai->sai_waitq);
-        return rc;
+       /* The "ll_sa_entry_to_stated()" will drop related ldlm ibits lock
+        * reference count by calling "ll_intent_drop_lock()" in spite of the
+        * above operations failed or not. Do not worry about calling
+        * "ll_intent_drop_lock()" more than once. */
+       rc = ll_sa_entry_to_stated(sai, entry,
+                                  rc < 0 ? SA_ENTRY_INVA : SA_ENTRY_SUCC);
+       if (rc == 0 && entry->se_index == sai->sai_index_wait)
+               wake_up(&sai->sai_waitq);
+       ll_sa_entry_put(sai, entry);
 }
 
 static int ll_statahead_interpret(struct ptlrpc_request *req,
-                                  struct md_enqueue_info *minfo,
-                                  int rc)
+                                  struct md_enqueue_info *minfo, int rc)
 {
-        struct lookup_intent     *it = &minfo->mi_it;
-        struct dentry            *dentry = minfo->mi_dentry;
+        struct lookup_intent     *it  = &minfo->mi_it;
         struct inode             *dir = minfo->mi_dir;
         struct ll_inode_info     *lli = ll_i2info(dir);
-        struct ll_statahead_info *sai;
-        struct ll_sai_entry      *entry;
+        struct ll_statahead_info *sai = NULL;
+        struct ll_sa_entry       *entry;
+        int                       wakeup;
         ENTRY;
 
-        CDEBUG(D_READA, "interpret statahead %.*s rc %d\n",
-               dentry->d_name.len, dentry->d_name.name, rc);
+        if (it_disposition(it, DISP_LOOKUP_NEG))
+                rc = -ENOENT;
+
+       spin_lock(&lli->lli_sa_lock);
+       /* stale entry */
+       if (unlikely(lli->lli_sai == NULL ||
+                    lli->lli_sai->sai_generation != minfo->mi_generation)) {
+               spin_unlock(&lli->lli_sa_lock);
+               GOTO(out, rc = -ESTALE);
+       } else {
+               sai = ll_sai_get(lli->lli_sai);
+               if (unlikely(!thread_is_running(&sai->sai_thread))) {
+                       sai->sai_replied++;
+                       spin_unlock(&lli->lli_sa_lock);
+                       GOTO(out, rc = -EBADFD);
+               }
+
+               entry = ll_sa_entry_get_byindex(sai, minfo->mi_cbdata);
+               if (entry == NULL) {
+                       sai->sai_replied++;
+                       spin_unlock(&lli->lli_sa_lock);
+                       GOTO(out, rc = -EIDRM);
+               }
+
+               if (rc != 0) {
+                       do_sa_entry_to_stated(sai, entry, SA_ENTRY_INVA);
+                       wakeup = (entry->se_index == sai->sai_index_wait);
+                } else {
+                       entry->se_minfo = minfo;
+                       entry->se_req = ptlrpc_request_addref(req);
+                       /* Release the async ibits lock ASAP to avoid deadlock
+                        * when statahead thread tries to enqueue lock on parent
+                        * for readpage and other tries to enqueue lock on child
+                        * with parent's lock held, for example: unlink. */
+                       entry->se_handle = it->d.lustre.it_lock_handle;
+                       ll_intent_drop_lock(it);
+                       wakeup = sa_received_empty(sai);
+                       list_add_tail(&entry->se_list,
+                                         &sai->sai_entries_received);
+                }
+               sai->sai_replied++;
+               spin_unlock(&lli->lli_sa_lock);
 
-        cfs_spin_lock(&lli->lli_lock);
-        if (unlikely(lli->lli_sai == NULL ||
-            lli->lli_sai->sai_generation != minfo->mi_generation)) {
-                cfs_spin_unlock(&lli->lli_lock);
+               ll_sa_entry_put(sai, entry);
+               if (wakeup)
+                       wake_up(&sai->sai_thread.t_ctl_waitq);
+        }
+
+        EXIT;
+
+out:
+        if (rc != 0) {
                 ll_intent_release(it);
-                dput(dentry);
                 iput(dir);
                 OBD_FREE_PTR(minfo);
-                RETURN(-ESTALE);
-        } else {
-                sai = ll_sai_get(lli->lli_sai);
-                entry = ll_sai_entry_set(sai,
-                                         (unsigned int)(long)minfo->mi_cbdata,
-                                         rc ? SA_ENTRY_UNSTATED :
-                                         SA_ENTRY_STATED, req, minfo);
-                LASSERT(entry != NULL);
-                if (likely(sa_is_running(sai))) {
-                        ll_sai_entry_to_received(sai, entry);
-                        sai->sai_replied++;
-                        cfs_spin_unlock(&lli->lli_lock);
-                        cfs_waitq_signal(&sai->sai_thread.t_ctl_waitq);
-                } else {
-                        if (!cfs_list_empty(&entry->se_list))
-                                cfs_list_del_init(&entry->se_list);
-                        sai->sai_replied++;
-                        cfs_spin_unlock(&lli->lli_lock);
-                        ll_sai_entry_cleanup(entry, 1);
-                }
-                ll_sai_put(sai);
-                RETURN(rc);
         }
+        if (sai != NULL)
+                ll_sai_put(sai);
+        return rc;
 }
 
 static void sa_args_fini(struct md_enqueue_info *minfo,
@@ -549,12 +798,13 @@ static void sa_args_fini(struct md_enqueue_info *minfo,
  * "ocapa". So here reserve "op_data.op_capa[1,2]" in "pcapa" before calling
  * "md_intent_getattr_async".
  */
-static int sa_args_init(struct inode *dir, struct dentry *dentry,
-                        struct md_enqueue_info **pmi,
+static int sa_args_init(struct inode *dir, struct inode *child,
+                        struct ll_sa_entry *entry, struct md_enqueue_info **pmi,
                         struct ldlm_enqueue_info **pei,
                         struct obd_capa **pcapa)
 {
-        struct ll_inode_info     *lli = ll_i2info(dir);
+        struct qstr              *qstr = &entry->se_qstr;
+        struct ll_inode_info     *lli  = ll_i2info(dir);
         struct md_enqueue_info   *minfo;
         struct ldlm_enqueue_info *einfo;
         struct md_op_data        *op_data;
@@ -569,9 +819,8 @@ static int sa_args_init(struct inode *dir, struct dentry *dentry,
                 return -ENOMEM;
         }
 
-        op_data = ll_prep_md_op_data(&minfo->mi_data, dir, dentry->d_inode,
-                                     dentry->d_name.name, dentry->d_name.len,
-                                     0, LUSTRE_OPC_ANY, NULL);
+        op_data = ll_prep_md_op_data(&minfo->mi_data, dir, child, qstr->name,
+                                     qstr->len, 0, LUSTRE_OPC_ANY, NULL);
         if (IS_ERR(op_data)) {
                 OBD_FREE_PTR(einfo);
                 OBD_FREE_PTR(minfo);
@@ -579,11 +828,10 @@ static int sa_args_init(struct inode *dir, struct dentry *dentry,
         }
 
         minfo->mi_it.it_op = IT_GETATTR;
-        minfo->mi_dentry = dentry;
         minfo->mi_dir = igrab(dir);
         minfo->mi_cb = ll_statahead_interpret;
         minfo->mi_generation = lli->lli_sai->sai_generation;
-        minfo->mi_cbdata = (void *)(long)lli->lli_sai->sai_index;
+        minfo->mi_cbdata = entry->se_index;
 
         einfo->ei_type   = LDLM_IBITS;
         einfo->ei_mode   = it_to_lock_mode(&minfo->mi_it);
@@ -600,10 +848,7 @@ static int sa_args_init(struct inode *dir, struct dentry *dentry,
         return 0;
 }
 
-/**
- * similar to ll_lookup_it().
- */
-static int do_sa_lookup(struct inode *dir, struct dentry *dentry)
+static int do_sa_lookup(struct inode *dir, struct ll_sa_entry *entry)
 {
         struct md_enqueue_info   *minfo;
         struct ldlm_enqueue_info *einfo;
@@ -611,7 +856,7 @@ static int do_sa_lookup(struct inode *dir, struct dentry *dentry)
         int                       rc;
         ENTRY;
 
-        rc = sa_args_init(dir, dentry, &minfo, &einfo, capas);
+        rc = sa_args_init(dir, NULL, entry, &minfo, &einfo, capas);
         if (rc)
                 RETURN(rc);
 
@@ -632,279 +877,452 @@ static int do_sa_lookup(struct inode *dir, struct dentry *dentry)
  * \retval      0 -- will send stat-ahead request
  * \retval others -- prepare stat-ahead request failed
  */
-static int do_sa_revalidate(struct inode *dir, struct dentry *dentry)
+static int do_sa_revalidate(struct inode *dir, struct ll_sa_entry *entry,
+                            struct dentry *dentry)
 {
         struct inode             *inode = dentry->d_inode;
-        struct lookup_intent      it = { .it_op = IT_GETATTR };
+        struct lookup_intent      it = { .it_op = IT_GETATTR,
+                                         .d.lustre.it_lock_handle = 0 };
         struct md_enqueue_info   *minfo;
         struct ldlm_enqueue_info *einfo;
         struct obd_capa          *capas[2];
         int rc;
         ENTRY;
 
-        if (inode == NULL)
+        if (unlikely(inode == NULL))
                 RETURN(1);
 
         if (d_mountpoint(dentry))
                 RETURN(1);
 
-        if (dentry == dentry->d_sb->s_root)
-                RETURN(1);
-
-        rc = md_revalidate_lock(ll_i2mdexp(dir), &it, ll_inode2fid(inode));
+        entry->se_inode = igrab(inode);
+        rc = md_revalidate_lock(ll_i2mdexp(dir), &it, ll_inode2fid(inode),NULL);
         if (rc == 1) {
+                entry->se_handle = it.d.lustre.it_lock_handle;
                 ll_intent_release(&it);
                 RETURN(1);
         }
 
-        rc = sa_args_init(dir, dentry, &minfo, &einfo, capas);
-        if (rc)
+        rc = sa_args_init(dir, inode, entry, &minfo, &einfo, capas);
+        if (rc) {
+                entry->se_inode = NULL;
+                iput(inode);
                 RETURN(rc);
+        }
 
         rc = md_intent_getattr_async(ll_i2mdexp(dir), minfo, einfo);
         if (!rc) {
                 capa_put(capas[0]);
                 capa_put(capas[1]);
         } else {
+                entry->se_inode = NULL;
+                iput(inode);
                 sa_args_fini(minfo, einfo);
         }
 
         RETURN(rc);
 }
 
-static inline void ll_name2qstr(struct qstr *q, const char *name, int namelen)
+static void ll_statahead_one(struct dentry *parent, const char* entry_name,
+                             int entry_name_len)
 {
-        q->name = name;
-        q->len  = namelen;
-        q->hash = full_name_hash(name, namelen);
-}
-
-static int ll_statahead_one(struct dentry *parent, const char* entry_name,
-                            int entry_name_len)
-{
-        struct inode             *dir = parent->d_inode;
-        struct ll_inode_info     *lli = ll_i2info(dir);
-        struct ll_statahead_info *sai = lli->lli_sai;
-        struct qstr               name;
-        struct dentry            *dentry;
-        struct ll_sai_entry      *se;
+        struct inode             *dir    = parent->d_inode;
+        struct ll_inode_info     *lli    = ll_i2info(dir);
+        struct ll_statahead_info *sai    = lli->lli_sai;
+        struct dentry            *dentry = NULL;
+        struct ll_sa_entry       *entry;
         int                       rc;
+        int                       rc1;
         ENTRY;
 
-        if (parent->d_flags & DCACHE_LUSTRE_INVALID) {
-                CDEBUG(D_READA, "parent dentry@%p %.*s is "
-                       "invalid, skip statahead\n",
-                       parent, parent->d_name.len, parent->d_name.name);
-                RETURN(-EINVAL);
-        }
-
-        se = ll_sai_entry_init(sai, sai->sai_index);
-        if (IS_ERR(se))
-                RETURN(PTR_ERR(se));
+        entry = ll_sa_entry_alloc(sai, sai->sai_index, entry_name,
+                                  entry_name_len);
+        if (IS_ERR(entry))
+                RETURN_EXIT;
 
-        ll_name2qstr(&name, entry_name, entry_name_len);
-        dentry = d_lookup(parent, &name);
+        dentry = d_lookup(parent, &entry->se_qstr);
         if (!dentry) {
-                dentry = d_alloc(parent, &name);
-                if (dentry) {
-                        rc = do_sa_lookup(dir, dentry);
-                        if (rc)
-                                dput(dentry);
-                } else {
-                        GOTO(out, rc = -ENOMEM);
-                }
+                rc = do_sa_lookup(dir, entry);
         } else {
-                rc = do_sa_revalidate(dir, dentry);
-                if (rc)
-                        dput(dentry);
+                rc = do_sa_revalidate(dir, entry, dentry);
+                if (rc == 1 && agl_should_run(sai, dentry->d_inode))
+                        ll_agl_add(sai, dentry->d_inode, entry->se_index);
         }
 
-        EXIT;
+        if (dentry != NULL)
+                dput(dentry);
 
-out:
-        if (rc) {
-                CDEBUG(D_READA, "set sai entry %p index %u stat %d rc %d\n",
-                       se, se->se_index, se->se_stat, rc);
-                se->se_stat = rc;
-                if (ll_sai_entry_to_stated(sai, se))
-                        cfs_waitq_signal(&sai->sai_waitq);
-        } else {
-                sai->sai_sent++;
-        }
+       if (rc) {
+               rc1 = ll_sa_entry_to_stated(sai, entry,
+                                       rc < 0 ? SA_ENTRY_INVA : SA_ENTRY_SUCC);
+               if (rc1 == 0 && entry->se_index == sai->sai_index_wait)
+                       wake_up(&sai->sai_waitq);
+       } else {
+               sai->sai_sent++;
+       }
 
         sai->sai_index++;
-        return rc;
+        /* drop one refcount on entry by ll_sa_entry_alloc */
+        ll_sa_entry_put(sai, entry);
+
+        EXIT;
 }
 
-static int ll_statahead_thread(void *arg)
+static int ll_agl_thread(void *arg)
 {
         struct dentry            *parent = (struct dentry *)arg;
-        struct inode             *dir = parent->d_inode;
-        struct ll_inode_info     *lli = ll_i2info(dir);
-        struct ll_sb_info        *sbi = ll_i2sbi(dir);
-        struct ll_statahead_info *sai = ll_sai_get(lli->lli_sai);
-        struct ptlrpc_thread     *thread = &sai->sai_thread;
-        struct page              *page;
-        __u64                     pos = 0;
-        int                       first = 0;
-        int                       rc = 0;
-        struct ll_dir_chain       chain;
+        struct inode             *dir    = parent->d_inode;
+        struct ll_inode_info     *plli   = ll_i2info(dir);
+        struct ll_inode_info     *clli;
+        struct ll_sb_info        *sbi    = ll_i2sbi(dir);
+        struct ll_statahead_info *sai    = ll_sai_get(plli->lli_sai);
+        struct ptlrpc_thread     *thread = &sai->sai_agl_thread;
+        struct l_wait_info        lwi    = { 0 };
         ENTRY;
 
-        {
-                char pname[16];
-                snprintf(pname, 15, "ll_sa_%u", lli->lli_opendir_pid);
-                cfs_daemonize(pname);
-        }
-
-        sbi->ll_sa_total++;
-        cfs_spin_lock(&lli->lli_lock);
-        thread->t_flags = SVC_RUNNING;
-        cfs_spin_unlock(&lli->lli_lock);
-        cfs_waitq_signal(&thread->t_ctl_waitq);
-        CDEBUG(D_READA, "start doing statahead for %s\n", parent->d_name.name);
-
-        ll_dir_chain_init(&chain);
-        page = ll_get_dir_page(dir, pos, 0, &chain);
+       thread->t_pid = current_pid();
+       CDEBUG(D_READA, "agl thread started: sai %p, parent %.*s\n",
+              sai, parent->d_name.len, parent->d_name.name);
+
+       atomic_inc(&sbi->ll_agl_total);
+       spin_lock(&plli->lli_agl_lock);
+       sai->sai_agl_valid = 1;
+       if (thread_is_init(thread))
+               /* If someone else has changed the thread state
+                * (e.g. already changed to SVC_STOPPING), we can't just
+                * blindly overwrite that setting. */
+               thread_set_flags(thread, SVC_RUNNING);
+       spin_unlock(&plli->lli_agl_lock);
+       wake_up(&thread->t_ctl_waitq);
 
         while (1) {
-                struct l_wait_info lwi = { 0 };
-                struct lu_dirpage *dp;
-                struct lu_dirent  *ent;
-
-                if (IS_ERR(page)) {
-                        rc = PTR_ERR(page);
-                        CDEBUG(D_READA, "error reading dir "DFID" at "LPU64"/%u: rc %d\n",
-                               PFID(ll_inode2fid(dir)), pos,
-                               sai->sai_index, rc);
-                        break;
-                }
-
-                dp = page_address(page);
-                for (ent = lu_dirent_start(dp); ent != NULL;
-                     ent = lu_dirent_next(ent)) {
-                        char *name = ent->lde_name;
-                        int namelen = le16_to_cpu(ent->lde_namelen);
-
-                        if (namelen == 0)
-                                /*
-                                 * Skip dummy record.
-                                 */
-                                continue;
-
-                        if (name[0] == '.') {
-                                if (namelen == 1) {
-                                        /*
-                                         * skip "."
-                                         */
-                                        continue;
-                                } else if (name[1] == '.' && namelen == 2) {
-                                        /*
-                                         * skip ".."
-                                         */
-                                        continue;
-                                } else if (!sai->sai_ls_all) {
-                                        /*
-                                         * skip hidden files.
-                                         */
-                                        sai->sai_skip_hidden++;
-                                        continue;
-                                }
-                        }
-
-                        /*
-                         * don't stat-ahead first entry.
-                         */
-                        if (unlikely(!first)) {
-                                first++;
-                                continue;
-                        }
-
-keep_de:
-                        l_wait_event(thread->t_ctl_waitq,
-                                     !sa_is_running(sai) || sa_not_full(sai) ||
-                                     !sa_received_empty(sai),
-                                     &lwi);
-
-                        while (!sa_received_empty(sai) && sa_is_running(sai))
-                                do_statahead_interpret(sai);
+                l_wait_event(thread->t_ctl_waitq,
+                             !agl_list_empty(sai) ||
+                             !thread_is_running(thread),
+                             &lwi);
 
-                        if (unlikely(!sa_is_running(sai))) {
-                                ll_put_page(page);
-                                GOTO(out, rc);
-                        }
+                if (!thread_is_running(thread))
+                        break;
 
-                        if (!sa_not_full(sai))
-                                /*
-                                 * do not skip the current de.
-                                 */
-                                goto keep_de;
+               spin_lock(&plli->lli_agl_lock);
+               /* The statahead thread maybe help to process AGL entries,
+                * so check whether list empty again. */
+               if (!agl_list_empty(sai)) {
+                       clli = agl_first_entry(sai);
+                       list_del_init(&clli->lli_agl_list);
+                       spin_unlock(&plli->lli_agl_lock);
+                       ll_agl_trigger(&clli->lli_vfs_inode, sai);
+               } else {
+                       spin_unlock(&plli->lli_agl_lock);
+               }
+       }
+
+       spin_lock(&plli->lli_agl_lock);
+       sai->sai_agl_valid = 0;
+       while (!agl_list_empty(sai)) {
+               clli = agl_first_entry(sai);
+               list_del_init(&clli->lli_agl_list);
+               spin_unlock(&plli->lli_agl_lock);
+               clli->lli_agl_index = 0;
+               iput(&clli->lli_vfs_inode);
+               spin_lock(&plli->lli_agl_lock);
+       }
+       thread_set_flags(thread, SVC_STOPPED);
+       spin_unlock(&plli->lli_agl_lock);
+       wake_up(&thread->t_ctl_waitq);
+       ll_sai_put(sai);
+       CDEBUG(D_READA, "agl thread stopped: sai %p, parent %.*s\n",
+              sai, parent->d_name.len, parent->d_name.name);
+       RETURN(0);
+}
 
-                        rc = ll_statahead_one(parent, name, namelen);
-                        if (rc < 0) {
-                                ll_put_page(page);
-                                GOTO(out, rc);
-                        }
-                }
-                pos = le64_to_cpu(dp->ldp_hash_end);
-                ll_put_page(page);
-                if (pos == DIR_END_OFF) {
-                        /*
-                         * End of directory reached.
-                         */
-                        while (1) {
-                                l_wait_event(thread->t_ctl_waitq,
-                                             !sa_is_running(sai) ||
-                                             !sa_received_empty(sai) ||
-                                             sai->sai_sent == sai->sai_replied,
-                                             &lwi);
-                                if (!sa_received_empty(sai) &&
-                                    sa_is_running(sai))
-                                        do_statahead_interpret(sai);
-                                else
-                                        GOTO(out, rc);
-                        }
-                } else if (1) {
-                        /*
-                         * chain is exhausted.
-                         * Normal case: continue to the next page.
-                         */
-                        page = ll_get_dir_page(dir, pos, 1, &chain);
-                } else {
-                        /*
-                         * go into overflow page.
-                         */
-                }
-        }
-        EXIT;
+static void ll_start_agl(struct dentry *parent, struct ll_statahead_info *sai)
+{
+       struct ptlrpc_thread *thread = &sai->sai_agl_thread;
+       struct l_wait_info    lwi    = { 0 };
+       struct ll_inode_info  *plli;
+       struct task_struct            *task;
+       ENTRY;
+
+       CDEBUG(D_READA, "start agl thread: sai %p, parent %.*s\n",
+              sai, parent->d_name.len, parent->d_name.name);
+
+       plli = ll_i2info(parent->d_inode);
+       task = kthread_run(ll_agl_thread, parent,
+                              "ll_agl_%u", plli->lli_opendir_pid);
+       if (IS_ERR(task)) {
+               CERROR("can't start ll_agl thread, rc: %ld\n", PTR_ERR(task));
+               thread_set_flags(thread, SVC_STOPPED);
+               RETURN_EXIT;
+       }
+
+       l_wait_event(thread->t_ctl_waitq,
+                    thread_is_running(thread) || thread_is_stopped(thread),
+                    &lwi);
+       EXIT;
+}
 
+static int ll_statahead_thread(void *arg)
+{
+       struct dentry            *parent = (struct dentry *)arg;
+       struct inode             *dir    = parent->d_inode;
+       struct ll_inode_info     *plli   = ll_i2info(dir);
+       struct ll_inode_info     *clli;
+       struct ll_sb_info        *sbi    = ll_i2sbi(dir);
+       struct ll_statahead_info *sai    = ll_sai_get(plli->lli_sai);
+       struct ptlrpc_thread     *thread = &sai->sai_thread;
+       struct ptlrpc_thread *agl_thread = &sai->sai_agl_thread;
+       int                       first  = 0;
+       int                       rc     = 0;
+       struct md_op_data        *op_data;
+       struct ll_dir_chain       chain;
+       struct l_wait_info        lwi    = { 0 };
+       struct page             *page = NULL;
+       __u64                   pos = 0;
+       ENTRY;
+
+       thread->t_pid = current_pid();
+       CDEBUG(D_READA, "statahead thread starting: sai %p, parent %.*s\n",
+              sai, parent->d_name.len, parent->d_name.name);
+
+       op_data = ll_prep_md_op_data(NULL, dir, dir, NULL, 0, 0,
+                                    LUSTRE_OPC_ANY, dir);
+       if (IS_ERR(op_data))
+               GOTO(out_put, rc = PTR_ERR(op_data));
+
+       op_data->op_max_pages = ll_i2sbi(dir)->ll_md_brw_pages;
+
+       if (sbi->ll_flags & LL_SBI_AGL_ENABLED)
+               ll_start_agl(parent, sai);
+
+       atomic_inc(&sbi->ll_sa_total);
+       spin_lock(&plli->lli_sa_lock);
+       if (thread_is_init(thread))
+               /* If someone else has changed the thread state
+                * (e.g. already changed to SVC_STOPPING), we can't just
+                * blindly overwrite that setting. */
+               thread_set_flags(thread, SVC_RUNNING);
+       spin_unlock(&plli->lli_sa_lock);
+       wake_up(&thread->t_ctl_waitq);
+
+       ll_dir_chain_init(&chain);
+       page = ll_get_dir_page(dir, op_data, pos, &chain);
+       while (1) {
+               struct lu_dirpage *dp;
+               struct lu_dirent  *ent;
+
+               if (IS_ERR(page)) {
+                       rc = PTR_ERR(page);
+                       CDEBUG(D_READA, "error reading dir "DFID" at "LPU64
+                              "/"LPU64" opendir_pid = %u: rc = %d\n",
+                              PFID(ll_inode2fid(dir)), pos, sai->sai_index,
+                              plli->lli_opendir_pid, rc);
+                       GOTO(out, rc);
+               }
+
+               dp = page_address(page);
+               for (ent = lu_dirent_start(dp); ent != NULL;
+                    ent = lu_dirent_next(ent)) {
+                       __u64 hash;
+                       int namelen;
+                       char *name;
+
+                       hash = le64_to_cpu(ent->lde_hash);
+                       if (unlikely(hash < pos))
+                               /*
+                                * Skip until we find target hash value.
+                                */
+                               continue;
+
+                       namelen = le16_to_cpu(ent->lde_namelen);
+                       if (unlikely(namelen == 0))
+                               /*
+                                * Skip dummy record.
+                                */
+                               continue;
+
+                       name = ent->lde_name;
+                       if (name[0] == '.') {
+                               if (namelen == 1) {
+                                       /*
+                                        * skip "."
+                                        */
+                                       continue;
+                               } else if (name[1] == '.' && namelen == 2) {
+                                       /*
+                                        * skip ".."
+                                        */
+                                       continue;
+                               } else if (!sai->sai_ls_all) {
+                                       /*
+                                        * skip hidden files.
+                                        */
+                                       sai->sai_skip_hidden++;
+                                       continue;
+                               }
+                       }
+
+                       /*
+                        * don't stat-ahead first entry.
+                        */
+                       if (unlikely(++first == 1))
+                               continue;
+
+keep_it:
+                       l_wait_event(thread->t_ctl_waitq,
+                                    !sa_sent_full(sai) ||
+                                    !sa_received_empty(sai) ||
+                                    !agl_list_empty(sai) ||
+                                    !thread_is_running(thread),
+                                    &lwi);
+
+interpret_it:
+                       while (!sa_received_empty(sai))
+                               ll_post_statahead(sai);
+
+                       if (unlikely(!thread_is_running(thread))) {
+                               ll_release_page(dir, page, false);
+                               GOTO(out, rc = 0);
+                       }
+
+                       /* If no window for metadata statahead, but there are
+                        * some AGL entries to be triggered, then try to help
+                        * to process the AGL entries. */
+                       if (sa_sent_full(sai)) {
+                               spin_lock(&plli->lli_agl_lock);
+                               while (!agl_list_empty(sai)) {
+                                       clli = agl_first_entry(sai);
+                                       list_del_init(&clli->lli_agl_list);
+                                       spin_unlock(&plli->lli_agl_lock);
+                                       ll_agl_trigger(&clli->lli_vfs_inode,
+                                                      sai);
+
+                                       if (!sa_received_empty(sai))
+                                               goto interpret_it;
+
+                                       if (unlikely(
+                                               !thread_is_running(thread))) {
+                                               ll_release_page(dir, page,
+                                                               false);
+                                               GOTO(out, rc = 0);
+                                       }
+
+                                       if (!sa_sent_full(sai))
+                                               goto do_it;
+
+                                       spin_lock(&plli->lli_agl_lock);
+                               }
+                               spin_unlock(&plli->lli_agl_lock);
+
+                               goto keep_it;
+                       }
+do_it:
+                       ll_statahead_one(parent, name, namelen);
+               }
+
+               pos = le64_to_cpu(dp->ldp_hash_end);
+               if (pos == MDS_DIR_END_OFF) {
+                       /*
+                        * End of directory reached.
+                        */
+                       ll_release_page(dir, page, false);
+                       while (1) {
+                               l_wait_event(thread->t_ctl_waitq,
+                                            !sa_received_empty(sai) ||
+                                           sai->sai_sent == sai->sai_replied ||
+                                            !thread_is_running(thread),
+                                            &lwi);
+
+                               while (!sa_received_empty(sai))
+                                       ll_post_statahead(sai);
+
+                               if (unlikely(!thread_is_running(thread)))
+                                       GOTO(out, rc = 0);
+
+                               if (sai->sai_sent == sai->sai_replied &&
+                                   sa_received_empty(sai))
+                                       break;
+                       }
+
+                       spin_lock(&plli->lli_agl_lock);
+                       while (!agl_list_empty(sai) &&
+                              thread_is_running(thread)) {
+                               clli = agl_first_entry(sai);
+                               list_del_init(&clli->lli_agl_list);
+                               spin_unlock(&plli->lli_agl_lock);
+                               ll_agl_trigger(&clli->lli_vfs_inode, sai);
+                               spin_lock(&plli->lli_agl_lock);
+                       }
+                       spin_unlock(&plli->lli_agl_lock);
+
+                       GOTO(out, rc = 0);
+               } else {
+                       /*
+                        * chain is exhausted.
+                        * Normal case: continue to the next page.
+                        */
+                       ll_release_page(dir, page, le32_to_cpu(dp->ldp_flags) &
+                                             LDF_COLLIDE);
+                       sai->sai_in_readpage = 1;
+                       page = ll_get_dir_page(dir, op_data, pos, &chain);
+                       sai->sai_in_readpage = 0;
+               }
+       }
 out:
-        ll_dir_chain_fini(&chain);
-        cfs_spin_lock(&lli->lli_lock);
-        thread->t_flags = SVC_STOPPED;
-        cfs_spin_unlock(&lli->lli_lock);
-        cfs_waitq_signal(&sai->sai_waitq);
-        cfs_waitq_signal(&thread->t_ctl_waitq);
+       EXIT;
+       ll_dir_chain_fini(&chain);
+       ll_finish_md_op_data(op_data);
+out_put:
+        if (sai->sai_agl_valid) {
+               spin_lock(&plli->lli_agl_lock);
+               thread_set_flags(agl_thread, SVC_STOPPING);
+               spin_unlock(&plli->lli_agl_lock);
+               wake_up(&agl_thread->t_ctl_waitq);
+
+               CDEBUG(D_READA, "stop agl thread: sai %p pid %u\n",
+                      sai, (unsigned int)agl_thread->t_pid);
+               l_wait_event(agl_thread->t_ctl_waitq,
+                            thread_is_stopped(agl_thread),
+                            &lwi);
+        } else {
+                /* Set agl_thread flags anyway. */
+                thread_set_flags(&sai->sai_agl_thread, SVC_STOPPED);
+        }
+       spin_lock(&plli->lli_sa_lock);
+       if (!sa_received_empty(sai)) {
+               thread_set_flags(thread, SVC_STOPPING);
+               spin_unlock(&plli->lli_sa_lock);
+
+               /* To release the resources held by received entries. */
+               while (!sa_received_empty(sai))
+                       ll_post_statahead(sai);
+
+               spin_lock(&plli->lli_sa_lock);
+       }
+       thread_set_flags(thread, SVC_STOPPED);
+       spin_unlock(&plli->lli_sa_lock);
+       wake_up(&sai->sai_waitq);
+       wake_up(&thread->t_ctl_waitq);
         ll_sai_put(sai);
-        dput(parent);
-        CDEBUG(D_READA, "statahead thread stopped, pid %d\n",
-               cfs_curproc_pid());
-        return rc;
+       CDEBUG(D_READA, "statahead thread stopped: sai %p, parent %.*s\n",
+              sai, parent->d_name.len, parent->d_name.name);
+       dput(parent);
+       return rc;
 }
 
 /**
  * called in ll_file_release().
  */
-void ll_stop_statahead(struct inode *inode, void *key)
+void ll_stop_statahead(struct inode *dir, void *key)
 {
-        struct ll_inode_info *lli = ll_i2info(inode);
+       struct ll_inode_info *lli = ll_i2info(dir);
 
-        if (unlikely(key == NULL))
-                return;
+       if (unlikely(key == NULL))
+               return;
 
-        cfs_spin_lock(&lli->lli_lock);
-        if (lli->lli_opendir_key != key || lli->lli_opendir_pid == 0) {
-                cfs_spin_unlock(&lli->lli_lock);
+       spin_lock(&lli->lli_sa_lock);
+       if (lli->lli_opendir_key != key || lli->lli_opendir_pid == 0) {
+               spin_unlock(&lli->lli_sa_lock);
                 return;
         }
 
@@ -914,30 +1332,30 @@ void ll_stop_statahead(struct inode *inode, void *key)
                 struct l_wait_info lwi = { 0 };
                 struct ptlrpc_thread *thread = &lli->lli_sai->sai_thread;
 
-                if (!sa_is_stopped(lli->lli_sai)) {
-                        thread->t_flags = SVC_STOPPING;
-                        cfs_spin_unlock(&lli->lli_lock);
-                        cfs_waitq_signal(&thread->t_ctl_waitq);
-
-                        CDEBUG(D_READA, "stopping statahead thread, pid %d\n",
-                               cfs_curproc_pid());
-                        l_wait_event(thread->t_ctl_waitq,
-                                     sa_is_stopped(lli->lli_sai),
-                                     &lwi);
-                } else {
-                        cfs_spin_unlock(&lli->lli_lock);
-                }
-
-                /*
-                 * Put the ref which was held when first statahead_enter.
-                 * It maybe not the last ref for some statahead requests
-                 * maybe inflight.
-                 */
-                ll_sai_put(lli->lli_sai);
-        } else {
-                lli->lli_opendir_pid = 0;
-                cfs_spin_unlock(&lli->lli_lock);
-        }
+                if (!thread_is_stopped(thread)) {
+                        thread_set_flags(thread, SVC_STOPPING);
+                       spin_unlock(&lli->lli_sa_lock);
+                       wake_up(&thread->t_ctl_waitq);
+
+                       CDEBUG(D_READA, "stop statahead thread: sai %p pid %u\n",
+                              lli->lli_sai, (unsigned int)thread->t_pid);
+                       l_wait_event(thread->t_ctl_waitq,
+                                    thread_is_stopped(thread),
+                                    &lwi);
+               } else {
+                       spin_unlock(&lli->lli_sa_lock);
+               }
+
+               /*
+                * Put the ref which was held when first statahead_enter.
+                * It maybe not the last ref for some statahead requests
+                * maybe inflight.
+                */
+               ll_sai_put(lli->lli_sai);
+       } else {
+               lli->lli_opendir_pid = 0;
+               spin_unlock(&lli->lli_sa_lock);
+       }
 }
 
 enum {
@@ -950,142 +1368,213 @@ enum {
          */
         LS_FIRST_DE,
         /**
-         * the first hidden dirent, that is "." 
+         * the first hidden dirent, that is "."
          */
         LS_FIRST_DOT_DE
 };
 
 static int is_first_dirent(struct inode *dir, struct dentry *dentry)
 {
-        struct ll_dir_chain chain;
-        struct qstr        *target = &dentry->d_name;
-        struct page        *page;
-        __u64               pos = 0;
-        int                 dot_de;
-        int                 rc = LS_NONE_FIRST_DE;
-        ENTRY;
-
-        ll_dir_chain_init(&chain);
-        page = ll_get_dir_page(dir, pos, 0, &chain);
-
-        while (1) {
-                struct lu_dirpage *dp;
-                struct lu_dirent  *ent;
-
-                if (IS_ERR(page)) {
-                        rc = PTR_ERR(page);
-                        CERROR("error reading dir "DFID" at "LPU64": rc %d\n",
-                               PFID(ll_inode2fid(dir)), pos, rc);
-                        break;
-                }
-
-                dp = page_address(page);
-                for (ent = lu_dirent_start(dp); ent != NULL;
-                     ent = lu_dirent_next(ent)) {
-                        char *name = ent->lde_name;
-                        int namelen = le16_to_cpu(ent->lde_namelen);
-
-                        if (namelen == 0)
-                                /*
-                                 * skip dummy record.
-                                 */
-                                continue;
-
-                        if (name[0] == '.') {
-                                if (namelen == 1)
-                                        /*
-                                         * skip "."
-                                         */
-                                        continue;
-                                else if (name[1] == '.' && namelen == 2)
-                                        /*
-                                         * skip ".."
-                                         */
-                                        continue;
-                                else
-                                        dot_de = 1;
-                        } else {
-                                dot_de = 0;
-                        }
-
-                        if (dot_de && target->name[0] != '.') {
-                                CDEBUG(D_READA, "%.*s skip hidden file %.*s\n",
-                                       target->len, target->name,
-                                       namelen, name);
-                                continue;
-                        }
+       struct ll_dir_chain   chain;
+       struct qstr          *target = &dentry->d_name;
+       struct md_op_data    *op_data;
+       int                   dot_de;
+       struct page          *page = NULL;
+       int                   rc     = LS_NONE_FIRST_DE;
+       __u64                 pos = 0;
+       ENTRY;
+
+       op_data = ll_prep_md_op_data(NULL, dir, dir, NULL, 0, 0,
+                                    LUSTRE_OPC_ANY, dir);
+       if (IS_ERR(op_data))
+               RETURN(PTR_ERR(op_data));
+       /**
+        *FIXME choose the start offset of the readdir
+        */
+       op_data->op_stripe_offset = 0;
+       op_data->op_max_pages = ll_i2sbi(dir)->ll_md_brw_pages;
+
+       ll_dir_chain_init(&chain);
+       page = ll_get_dir_page(dir, op_data, 0, &chain);
+
+       while (1) {
+               struct lu_dirpage *dp;
+               struct lu_dirent  *ent;
+
+               if (IS_ERR(page)) {
+                       struct ll_inode_info *lli = ll_i2info(dir);
+
+                       rc = PTR_ERR(page);
+                       CERROR("%s: reading dir "DFID" at "LPU64
+                              "opendir_pid = %u : rc = %d\n",
+                              ll_get_fsname(dir->i_sb, NULL, 0),
+                              PFID(ll_inode2fid(dir)), pos,
+                              lli->lli_opendir_pid, rc);
+                       break;
+               }
+
+               dp = page_address(page);
+               for (ent = lu_dirent_start(dp); ent != NULL;
+                    ent = lu_dirent_next(ent)) {
+                       __u64 hash;
+                       int namelen;
+                       char *name;
+
+                       hash = le64_to_cpu(ent->lde_hash);
+                       /* The ll_get_dir_page() can return any page containing
+                        * the given hash which may be not the start hash. */
+                       if (unlikely(hash < pos))
+                               continue;
+
+                       namelen = le16_to_cpu(ent->lde_namelen);
+                       if (unlikely(namelen == 0))
+                               /*
+                                * skip dummy record.
+                                */
+                               continue;
+
+                       name = ent->lde_name;
+                       if (name[0] == '.') {
+                               if (namelen == 1)
+                                       /*
+                                        * skip "."
+                                        */
+                                       continue;
+                               else if (name[1] == '.' && namelen == 2)
+                                       /*
+                                        * skip ".."
+                                        */
+                                       continue;
+                               else
+                                       dot_de = 1;
+                       } else {
+                               dot_de = 0;
+                       }
+
+                       if (dot_de && target->name[0] != '.') {
+                               CDEBUG(D_READA, "%.*s skip hidden file %.*s\n",
+                                      target->len, target->name,
+                                      namelen, name);
+                               continue;
+                       }
+
+                       if (target->len != namelen ||
+                           memcmp(target->name, name, namelen) != 0)
+                               rc = LS_NONE_FIRST_DE;
+                       else if (!dot_de)
+                               rc = LS_FIRST_DE;
+                       else
+                               rc = LS_FIRST_DOT_DE;
+
+                       ll_release_page(dir, page, false);
+                       GOTO(out, rc);
+               }
+               pos = le64_to_cpu(dp->ldp_hash_end);
+               if (pos == MDS_DIR_END_OFF) {
+                       /*
+                        * End of directory reached.
+                        */
+                       ll_release_page(dir, page, false);
+                       GOTO(out, rc);
+               } else {
+                       /*
+                        * chain is exhausted
+                        * Normal case: continue to the next page.
+                        */
+                       ll_release_page(dir, page, le32_to_cpu(dp->ldp_flags) &
+                                             LDF_COLLIDE);
+                       page = ll_get_dir_page(dir, op_data, pos, &chain);
+               }
+       }
+       EXIT;
+out:
+       ll_dir_chain_fini(&chain);
+       ll_finish_md_op_data(op_data);
+        return rc;
+}
 
-                        if (target->len != namelen ||
-                            memcmp(target->name, name, namelen) != 0)
-                                rc = LS_NONE_FIRST_DE;
-                        else if (!dot_de)
-                                rc = LS_FIRST_DE;
-                        else
-                                rc = LS_FIRST_DOT_DE;
+static void
+ll_sai_unplug(struct ll_statahead_info *sai, struct ll_sa_entry *entry)
+{
+        struct ptlrpc_thread *thread = &sai->sai_thread;
+        struct ll_sb_info    *sbi    = ll_i2sbi(sai->sai_inode);
+        int                   hit;
+        ENTRY;
 
-                        ll_put_page(page);
-                        GOTO(out, rc);
-                }
-                pos = le64_to_cpu(dp->ldp_hash_end);
-                ll_put_page(page);
-                if (pos == DIR_END_OFF) {
-                        /*
-                         * End of directory reached.
-                         */
-                        break;
-                } else if (1) {
-                        /*
-                         * chain is exhausted
-                         * Normal case: continue to the next page.
-                         */
-                        page = ll_get_dir_page(dir, pos, 1, &chain);
-                } else {
-                        /*
-                         * go into overflow page.
-                         */
-                }
-        }
-        EXIT;
+        if (entry != NULL && entry->se_stat == SA_ENTRY_SUCC)
+                hit = 1;
+        else
+                hit = 0;
 
-out:
-        ll_dir_chain_fini(&chain);
-        return rc;
+        ll_sa_entry_fini(sai, entry);
+        if (hit) {
+                sai->sai_hit++;
+                sai->sai_consecutive_miss = 0;
+                sai->sai_max = min(2 * sai->sai_max, sbi->ll_sa_max);
+        } else {
+                struct ll_inode_info *lli = ll_i2info(sai->sai_inode);
+
+               sai->sai_miss++;
+               sai->sai_consecutive_miss++;
+               if (sa_low_hit(sai) && thread_is_running(thread)) {
+                       atomic_inc(&sbi->ll_sa_wrong);
+                       CDEBUG(D_READA, "Statahead for dir "DFID" hit "
+                              "ratio too low: hit/miss "LPU64"/"LPU64
+                              ", sent/replied "LPU64"/"LPU64", stopping "
+                              "statahead thread\n",
+                              PFID(&lli->lli_fid), sai->sai_hit,
+                              sai->sai_miss, sai->sai_sent,
+                              sai->sai_replied);
+                       spin_lock(&lli->lli_sa_lock);
+                       if (!thread_is_stopped(thread))
+                               thread_set_flags(thread, SVC_STOPPING);
+                       spin_unlock(&lli->lli_sa_lock);
+               }
+       }
+
+       if (!thread_is_stopped(thread))
+               wake_up(&thread->t_ctl_waitq);
+
+       EXIT;
 }
 
 /**
  * Start statahead thread if this is the first dir entry.
  * Otherwise if a thread is started already, wait it until it is ahead of me.
- * \retval 0       -- stat ahead thread process such dentry, for lookup, it miss
- * \retval 1       -- stat ahead thread process such dentry, for lookup, it hit
- * \retval -EEXIST -- stat ahead thread started, and this is the first dentry
- * \retval -EBADFD -- statahead thread exit and not dentry available
- * \retval -EAGAIN -- try to stat by caller
- * \retval others  -- error
+ * \retval 1       -- find entry with lock in cache, the caller needs to do
+ *                    nothing.
+ * \retval 0       -- find entry in cache, but without lock, the caller needs
+ *                    refresh from MDS.
+ * \retval others  -- the caller need to process as non-statahead.
  */
-int do_statahead_enter(struct inode *dir, struct dentry **dentryp, int lookup)
+int do_statahead_enter(struct inode *dir, struct dentry **dentryp,
+                       int only_unplug)
 {
-        struct ll_inode_info     *lli;
-        struct ll_statahead_info *sai;
-        struct dentry            *parent;
-        struct l_wait_info        lwi = LWI_INTR(LWI_ON_SIGNAL_NOOP, NULL);
-        int                       rc = 0;
-        ENTRY;
-
-        LASSERT(dir != NULL);
-        lli = ll_i2info(dir);
-        LASSERT(lli->lli_opendir_pid == cfs_curproc_pid());
-        sai = lli->lli_sai;
+       struct ll_inode_info            *lli = ll_i2info(dir);
+       struct ll_statahead_info        *sai = lli->lli_sai;
+       struct dentry                   *parent;
+       struct ll_sa_entry              *entry;
+       struct ptlrpc_thread            *thread;
+       struct l_wait_info               lwi = { 0 };
+       struct task_struct              *task;
+       int                              rc = 0;
+       struct ll_inode_info            *plli;
+       ENTRY;
+
+       LASSERT(lli->lli_opendir_pid == current_pid());
 
         if (sai) {
-                struct ll_sb_info *sbi;
-
-                if (unlikely(sa_is_stopped(sai) &&
-                             cfs_list_empty(&sai->sai_entries_stated)))
-                        RETURN(-EBADFD);
+                thread = &sai->sai_thread;
+                if (unlikely(thread_is_stopped(thread) &&
+                            list_empty(&sai->sai_entries_stated))) {
+                        /* to release resource */
+                        ll_stop_statahead(dir, lli->lli_opendir_key);
+                        RETURN(-EAGAIN);
+                }
 
                 if ((*dentryp)->d_name.name[0] == '.') {
-                        if (likely(sai->sai_ls_all ||
-                            sai->sai_miss_hidden >= sai->sai_skip_hidden)) {
+                        if (sai->sai_ls_all ||
+                            sai->sai_miss_hidden >= sai->sai_skip_hidden) {
                                 /*
                                  * Hidden dentry is the first one, or statahead
                                  * thread does not skip so many hidden dentries
@@ -1106,40 +1595,83 @@ int do_statahead_enter(struct inode *dir, struct dentry **dentryp, int lookup)
                                  * "sai_ls_all" enabled as above.
                                  */
                                 sai->sai_miss_hidden++;
-                                RETURN(-ENOENT);
+                                RETURN(-EAGAIN);
                         }
                 }
 
-                sbi = ll_i2sbi(dir);
-                if (ll_sai_entry_stated(sai)) {
-                        sbi->ll_sa_cached++;
-                } else {
-                        sbi->ll_sa_blocked++;
-                        /*
-                         * thread started already, avoid double-stat.
-                         */
+                entry = ll_sa_entry_get_byname(sai, &(*dentryp)->d_name);
+                if (entry == NULL || only_unplug) {
+                        ll_sai_unplug(sai, entry);
+                        RETURN(entry ? 1 : -EAGAIN);
+                }
+
+               /* if statahead is busy in readdir, help it do post-work */
+               while (!ll_sa_entry_stated(entry) &&
+                      sai->sai_in_readpage && !sa_received_empty(sai))
+                       ll_post_statahead(sai);
+
+                if (!ll_sa_entry_stated(entry)) {
+                        sai->sai_index_wait = entry->se_index;
+                        lwi = LWI_TIMEOUT_INTR(cfs_time_seconds(30), NULL,
+                                               LWI_ON_SIGNAL_NOOP, NULL);
                         rc = l_wait_event(sai->sai_waitq,
-                                          ll_sai_entry_stated(sai) ||
-                                          sa_is_stopped(sai),
+                                          ll_sa_entry_stated(entry) ||
+                                          thread_is_stopped(thread),
                                           &lwi);
+                        if (rc < 0) {
+                                ll_sai_unplug(sai, entry);
+                                RETURN(-EAGAIN);
+                        }
                 }
 
-                if (lookup) {
-                        struct dentry *result;
-
-                        result = d_lookup((*dentryp)->d_parent,
-                                          &(*dentryp)->d_name);
-                        if (result) {
-                                LASSERT(result != *dentryp);
-                                /* BUG 16303: do not drop reference count for
-                                 * "*dentryp", VFS will do that by itself. */
-                                *dentryp = result;
-                                RETURN(1);
+                if (entry->se_stat == SA_ENTRY_SUCC &&
+                    entry->se_inode != NULL) {
+                        struct inode *inode = entry->se_inode;
+                        struct lookup_intent it = { .it_op = IT_GETATTR,
+                                                    .d.lustre.it_lock_handle =
+                                                     entry->se_handle };
+                       __u64 bits;
+
+                       rc = md_revalidate_lock(ll_i2mdexp(dir), &it,
+                                               ll_inode2fid(inode), &bits);
+                       if (rc == 1) {
+                               if ((*dentryp)->d_inode == NULL) {
+                                       struct dentry *alias;
+
+                                       alias = ll_splice_alias(inode,
+                                                               *dentryp);
+                                       if (IS_ERR(alias)) {
+                                               ll_sai_unplug(sai, entry);
+                                               RETURN(PTR_ERR(alias));
+                                       }
+                                       *dentryp = alias;
+                                } else if ((*dentryp)->d_inode != inode) {
+                                        /* revalidate, but inode is recreated */
+                                        CDEBUG(D_READA,
+                                              "%s: stale dentry %.*s inode "
+                                              DFID", statahead inode "DFID
+                                              "\n",
+                                              ll_get_fsname((*dentryp)->d_inode->i_sb, NULL, 0),
+                                              (*dentryp)->d_name.len,
+                                              (*dentryp)->d_name.name,
+                                              PFID(ll_inode2fid((*dentryp)->d_inode)),
+                                              PFID(ll_inode2fid(inode)));
+                                       ll_intent_release(&it);
+                                       ll_sai_unplug(sai, entry);
+                                        RETURN(-ESTALE);
+                                } else {
+                                       iput(inode);
+                               }
+                               entry->se_inode = NULL;
+
+                               if ((bits & MDS_INODELOCK_LOOKUP) &&
+                                   d_lustre_invalid(*dentryp))
+                                       d_lustre_revalidate(*dentryp);
+                                ll_intent_release(&it);
                         }
                 }
-                /*
-                 * do nothing for revalidate.
-                 */
+
+                ll_sai_unplug(sai, entry);
                 RETURN(rc);
         }
 
@@ -1156,9 +1688,8 @@ int do_statahead_enter(struct inode *dir, struct dentry **dentryp, int lookup)
         sai->sai_ls_all = (rc == LS_FIRST_DOT_DE);
         sai->sai_inode = igrab(dir);
         if (unlikely(sai->sai_inode == NULL)) {
-                CWARN("Do not start stat ahead on dying inode "DFID" .\n",
+                CWARN("Do not start stat ahead on dying inode "DFID"\n",
                       PFID(&lli->lli_fid));
-                OBD_FREE_PTR(sai);
                 GOTO(out, rc = -ESTALE);
         }
 
@@ -1168,92 +1699,61 @@ int do_statahead_enter(struct inode *dir, struct dentry **dentryp, int lookup)
                 struct ll_inode_info *nlli = ll_i2info(parent->d_inode);
 
                 CWARN("Race condition, someone changed %.*s just now: "
-                      "old parent "DFID", new parent "DFID" .\n",
+                      "old parent "DFID", new parent "DFID"\n",
                       (*dentryp)->d_name.len, (*dentryp)->d_name.name,
                       PFID(&lli->lli_fid), PFID(&nlli->lli_fid));
                 dput(parent);
                 iput(sai->sai_inode);
-                OBD_FREE_PTR(sai);
-                RETURN(-EAGAIN);
+                GOTO(out, rc = -EAGAIN);
         }
 
+       CDEBUG(D_READA, "start statahead thread: sai %p, parent %.*s\n",
+              sai, parent->d_name.len, parent->d_name.name);
+
+       /* The sai buffer already has one reference taken at allocation time,
+        * but as soon as we expose the sai by attaching it to the lli that
+        * default reference can be dropped by another thread calling
+        * ll_stop_statahead. We need to take a local reference to protect
+        * the sai buffer while we intend to access it. */
+        ll_sai_get(sai);
         lli->lli_sai = sai;
-        rc = cfs_kernel_thread(ll_statahead_thread, parent, 0);
-        if (rc < 0) {
-                CERROR("can't start ll_sa thread, rc: %d\n", rc);
-                dput(parent);
+
+       plli = ll_i2info(parent->d_inode);
+       task = kthread_run(ll_statahead_thread, parent, "ll_sa_%u",
+                          plli->lli_opendir_pid);
+       thread = &sai->sai_thread;
+       if (IS_ERR(task)) {
+               rc = PTR_ERR(task);
+               CERROR("cannot start ll_sa thread: rc = %d\n", rc);
+               dput(parent);
                 lli->lli_opendir_key = NULL;
-                sai->sai_thread.t_flags = SVC_STOPPED;
+                thread_set_flags(thread, SVC_STOPPED);
+                thread_set_flags(&sai->sai_agl_thread, SVC_STOPPED);
+               /* Drop both our own local reference and the default
+                * reference from allocation time. */
                 ll_sai_put(sai);
+               ll_sai_put(sai);
                 LASSERT(lli->lli_sai == NULL);
                 RETURN(-EAGAIN);
         }
 
-        l_wait_event(sai->sai_thread.t_ctl_waitq,
-                     sa_is_running(sai) || sa_is_stopped(sai),
+        l_wait_event(thread->t_ctl_waitq,
+                     thread_is_running(thread) || thread_is_stopped(thread),
                      &lwi);
+       ll_sai_put(sai);
 
         /*
          * We don't stat-ahead for the first dirent since we are already in
-         * lookup, and -EEXIST also indicates that this is the first dirent.
+         * lookup.
          */
-        RETURN(-EEXIST);
+        RETURN(-EAGAIN);
 
 out:
-        cfs_spin_lock(&lli->lli_lock);
-        lli->lli_opendir_key = NULL;
-        lli->lli_opendir_pid = 0;
-        cfs_spin_unlock(&lli->lli_lock);
-        return rc;
-}
-
-/**
- * update hit/miss count.
- */
-void ll_statahead_exit(struct inode *dir, struct dentry *dentry, int result)
-{
-        struct ll_inode_info     *lli;
-        struct ll_statahead_info *sai;
-        struct ll_sb_info        *sbi;
-        struct ll_dentry_data    *ldd = ll_d2d(dentry);
-        ENTRY;
-
-        LASSERT(dir != NULL);
-        lli = ll_i2info(dir);
-        LASSERT(lli->lli_opendir_pid == cfs_curproc_pid());
-        sai = lli->lli_sai;
-        LASSERT(sai != NULL);
-        sbi = ll_i2sbi(dir);
-
-        if (result >= 1) {
-                sbi->ll_sa_hit++;
-                sai->sai_hit++;
-                sai->sai_consecutive_miss = 0;
-                sai->sai_max = min(2 * sai->sai_max, sbi->ll_sa_max);
-        } else {
-                sbi->ll_sa_miss++;
-                sai->sai_miss++;
-                sai->sai_consecutive_miss++;
-                if (sa_low_hit(sai) && sa_is_running(sai)) {
-                        sbi->ll_sa_wrong++;
-                        CDEBUG(D_READA, "Statahead for dir "DFID" hit ratio "
-                               "too low: hit/miss %u/%u, sent/replied %u/%u, "
-                               "stopping statahead thread: pid %d\n",
-                               PFID(&lli->lli_fid), sai->sai_hit,
-                               sai->sai_miss, sai->sai_sent,
-                               sai->sai_replied, cfs_curproc_pid());
-                        cfs_spin_lock(&lli->lli_lock);
-                        if (!sa_is_stopped(sai))
-                                sai->sai_thread.t_flags = SVC_STOPPING;
-                        cfs_spin_unlock(&lli->lli_lock);
-                }
-        }
-
-        if (!sa_is_stopped(sai))
-                cfs_waitq_signal(&sai->sai_thread.t_ctl_waitq);
-        ll_sai_entry_fini(sai);
-        if (likely(ldd != NULL))
-                ldd->lld_sa_generation = sai->sai_generation;
-
-        EXIT;
+        if (sai != NULL)
+                OBD_FREE_PTR(sai);
+       spin_lock(&lli->lli_sa_lock);
+       lli->lli_opendir_key = NULL;
+       lli->lli_opendir_pid = 0;
+       spin_unlock(&lli->lli_sa_lock);
+       return rc;
 }