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LU-8918 obdclass: hoist locking in lu_context_exit()
[fs/lustre-release.git] / lustre / obdclass / lu_object.c
index dac8c2a..b633d26 100644 (file)
  *
  * You should have received a copy of the GNU General Public License
  * version 2 along with this program; If not, see
- * http://www.sun.com/software/products/lustre/docs/GPLv2.pdf
- *
- * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
- * CA 95054 USA or visit www.sun.com if you need additional information or
- * have any questions.
+ * http://www.gnu.org/licenses/gpl-2.0.html
  *
  * GPL HEADER END
  */
@@ -27,7 +23,7 @@
  * Copyright (c) 2007, 2010, Oracle and/or its affiliates. All rights reserved.
  * Use is subject to license terms.
  *
- * Copyright (c) 2011, 2014, Intel Corporation.
+ * Copyright (c) 2011, 2016, Intel Corporation.
  */
 /*
  * This file is part of Lustre, http://www.lustre.org/
@@ -44,8 +40,9 @@
 
 #define DEBUG_SUBSYSTEM S_CLASS
 
-#include <libcfs/libcfs.h>
 #include <linux/module.h>
+#include <linux/list.h>
+#include <libcfs/libcfs.h>
 #include <libcfs/libcfs_hash.h> /* hash_long() */
 #include <obd_class.h>
 #include <obd_support.h>
 #include <lustre_fid.h>
 #include <lu_object.h>
 #include <lu_ref.h>
-#include <libcfs/list.h>
 
 enum {
        LU_CACHE_PERCENT_MAX     = 50,
        LU_CACHE_PERCENT_DEFAULT = 20
 };
 
-#define        LU_CACHE_NR_MAX_ADJUST          128
+#define        LU_CACHE_NR_MAX_ADJUST          512
 #define        LU_CACHE_NR_UNLIMITED           -1
 #define        LU_CACHE_NR_DEFAULT             LU_CACHE_NR_UNLIMITED
 #define        LU_CACHE_NR_LDISKFS_LIMIT       LU_CACHE_NR_UNLIMITED
@@ -69,6 +65,7 @@ enum {
 
 #define LU_SITE_BITS_MIN    12
 #define LU_SITE_BITS_MAX    24
+#define LU_SITE_BITS_MAX_CL 19
 /**
  * total 256 buckets, we don't want too many buckets because:
  * - consume too much memory
@@ -78,14 +75,15 @@ enum {
 
 
 static unsigned int lu_cache_percent = LU_CACHE_PERCENT_DEFAULT;
-CFS_MODULE_PARM(lu_cache_percent, "i", int, 0644,
-               "Percentage of memory to be used as lu_object cache");
+module_param(lu_cache_percent, int, 0644);
+MODULE_PARM_DESC(lu_cache_percent, "Percentage of memory to be used as lu_object cache");
 
 static long lu_cache_nr = LU_CACHE_NR_DEFAULT;
-CFS_MODULE_PARM(lu_cache_nr, "l", long, 0644,
-               "Maximum number of objects in lu_object cache");
+module_param(lu_cache_nr, long, 0644);
+MODULE_PARM_DESC(lu_cache_nr, "Maximum number of objects in lu_object cache");
 
 static void lu_object_free(const struct lu_env *env, struct lu_object *o);
+static __u32 ls_stats_read(struct lprocfs_stats *stats, int idx);
 
 /**
  * Decrease reference counter on object. If last reference is freed, return
@@ -98,7 +96,7 @@ void lu_object_put(const struct lu_env *env, struct lu_object *o)
         struct lu_object_header *top;
         struct lu_site          *site;
         struct lu_object        *orig;
-        cfs_hash_bd_t            bd;
+       struct cfs_hash_bd            bd;
        const struct lu_fid     *fid;
 
         top  = o->lo_header;
@@ -154,12 +152,16 @@ void lu_object_put(const struct lu_env *env, struct lu_object *o)
                LASSERT(list_empty(&top->loh_lru));
                list_add_tail(&top->loh_lru, &bkt->lsb_lru);
                bkt->lsb_lru_len++;
+               percpu_counter_inc(&site->ls_lru_len_counter);
+               CDEBUG(D_INODE, "Add %p to site lru. hash: %p, bkt: %p, "
+                      "lru_len: %ld\n",
+                      o, site->ls_obj_hash, bkt, bkt->lsb_lru_len);
                 cfs_hash_bd_unlock(site->ls_obj_hash, &bd, 1);
                 return;
         }
 
         /*
-         * If object is dying (will not be cached), removed it
+        * If object is dying (will not be cached) then remove it
          * from hash table and LRU.
          *
          * This is done with hash table and LRU lists locked. As the only
@@ -202,8 +204,9 @@ void lu_object_unhash(const struct lu_env *env, struct lu_object *o)
        top = o->lo_header;
        set_bit(LU_OBJECT_HEARD_BANSHEE, &top->loh_flags);
        if (!test_and_set_bit(LU_OBJECT_UNHASHED, &top->loh_flags)) {
-               cfs_hash_t *obj_hash = o->lo_dev->ld_site->ls_obj_hash;
-               cfs_hash_bd_t bd;
+               struct lu_site *site = o->lo_dev->ld_site;
+               struct cfs_hash *obj_hash = site->ls_obj_hash;
+               struct cfs_hash_bd bd;
 
                cfs_hash_bd_get_and_lock(obj_hash, &top->loh_fid, &bd, 1);
                if (!list_empty(&top->loh_lru)) {
@@ -212,6 +215,7 @@ void lu_object_unhash(const struct lu_env *env, struct lu_object *o)
                        list_del_init(&top->loh_lru);
                        bkt = cfs_hash_bd_extra_get(obj_hash, &bd);
                        bkt->lsb_lru_len--;
+                       percpu_counter_dec(&site->ls_lru_len_counter);
                }
                cfs_hash_bd_del_locked(obj_hash, &bd, &top->loh_hash);
                cfs_hash_bd_unlock(obj_hash, &bd, 1);
@@ -340,17 +344,20 @@ static void lu_object_free(const struct lu_env *env, struct lu_object *o)
 
 /**
  * Free \a nr objects from the cold end of the site LRU list.
+ * if canblock is 0, then don't block awaiting for another
+ * instance of lu_site_purge() to complete
  */
-int lu_site_purge(const struct lu_env *env, struct lu_site *s, int nr)
+int lu_site_purge_objects(const struct lu_env *env, struct lu_site *s,
+                         int nr, int canblock)
 {
         struct lu_object_header *h;
         struct lu_object_header *temp;
         struct lu_site_bkt_data *bkt;
-        cfs_hash_bd_t            bd;
-        cfs_hash_bd_t            bd2;
+       struct cfs_hash_bd            bd;
+       struct cfs_hash_bd            bd2;
        struct list_head         dispose;
        int                      did_sth;
-       unsigned int             start;
+       unsigned int             start = 0;
         int                      count;
         int                      bnr;
        unsigned int             i;
@@ -363,14 +370,19 @@ int lu_site_purge(const struct lu_env *env, struct lu_site *s, int nr)
          * Under LRU list lock, scan LRU list and move unreferenced objects to
          * the dispose list, removing them from LRU and hash table.
          */
-        start = s->ls_purge_start;
+       if (nr != ~0)
+               start = s->ls_purge_start;
        bnr = (nr == ~0) ? -1 : nr / (int)CFS_HASH_NBKT(s->ls_obj_hash) + 1;
  again:
        /*
         * It doesn't make any sense to make purge threads parallel, that can
         * only bring troubles to us. See LU-5331.
         */
-       mutex_lock(&s->ls_purge_mutex);
+       if (canblock != 0)
+               mutex_lock(&s->ls_purge_mutex);
+       else if (mutex_trylock(&s->ls_purge_mutex) == 0)
+               goto out;
+
         did_sth = 0;
         cfs_hash_for_each_bucket(s->ls_obj_hash, &bd, i) {
                 if (i < start)
@@ -389,6 +401,7 @@ int lu_site_purge(const struct lu_env *env, struct lu_site *s, int nr)
                                                &bd2, &h->loh_hash);
                        list_move(&h->loh_lru, &dispose);
                        bkt->lsb_lru_len--;
+                       percpu_counter_dec(&s->ls_lru_len_counter);
                         if (did_sth == 0)
                                 did_sth = 1;
 
@@ -425,9 +438,10 @@ int lu_site_purge(const struct lu_env *env, struct lu_site *s, int nr)
         /* race on s->ls_purge_start, but nobody cares */
         s->ls_purge_start = i % CFS_HASH_NBKT(s->ls_obj_hash);
 
+out:
         return nr;
 }
-EXPORT_SYMBOL(lu_site_purge);
+EXPORT_SYMBOL(lu_site_purge_objects);
 
 /*
  * Object printing.
@@ -574,7 +588,7 @@ int lu_object_invariant(const struct lu_object *o)
 }
 
 static struct lu_object *htable_lookup(struct lu_site *s,
-                                      cfs_hash_bd_t *bd,
+                                      struct cfs_hash_bd *bd,
                                       const struct lu_fid *f,
                                       wait_queue_t *waiter,
                                       __u64 *version)
@@ -604,6 +618,7 @@ static struct lu_object *htable_lookup(struct lu_site *s,
                if (!list_empty(&h->loh_lru)) {
                        list_del_init(&h->loh_lru);
                        bkt->lsb_lru_len--;
+                       percpu_counter_dec(&s->ls_lru_len_counter);
                }
                 return lu_object_top(h);
         }
@@ -615,7 +630,7 @@ static struct lu_object *htable_lookup(struct lu_site *s,
          */
 
        if (likely(waiter != NULL)) {
-               init_waitqueue_entry_current(waiter);
+               init_waitqueue_entry(waiter, current);
                add_wait_queue(&bkt->lsb_marche_funebre, waiter);
                set_current_state(TASK_UNINTERRUPTIBLE);
                lprocfs_counter_incr(s->ls_stats, LU_SS_CACHE_DEATH_RACE);
@@ -654,11 +669,11 @@ static void lu_object_limit(const struct lu_env *env,
 
        size = cfs_hash_size_get(dev->ld_site->ls_obj_hash);
        nr = (__u64)lu_cache_nr;
-       if (size > nr)
-               lu_site_purge(env, dev->ld_site,
-                             MIN(size - nr, LU_CACHE_NR_MAX_ADJUST));
+       if (size <= nr)
+               return;
 
-       return;
+       lu_site_purge_objects(env, dev->ld_site,
+                             MIN(size - nr, LU_CACHE_NR_MAX_ADJUST), 0);
 }
 
 static struct lu_object *lu_object_new(const struct lu_env *env,
@@ -667,8 +682,8 @@ static struct lu_object *lu_object_new(const struct lu_env *env,
                                        const struct lu_object_conf *conf)
 {
         struct lu_object        *o;
-        cfs_hash_t              *hs;
-        cfs_hash_bd_t            bd;
+       struct cfs_hash              *hs;
+       struct cfs_hash_bd            bd;
 
         o = lu_object_alloc(env, dev, f, conf);
         if (unlikely(IS_ERR(o)))
@@ -696,8 +711,8 @@ static struct lu_object *lu_object_find_try(const struct lu_env *env,
        struct lu_object      *o;
        struct lu_object      *shadow;
        struct lu_site        *s;
-       cfs_hash_t            *hs;
-       cfs_hash_bd_t          bd;
+       struct cfs_hash            *hs;
+       struct cfs_hash_bd          bd;
        __u64                  version = 0;
 
         /*
@@ -784,7 +799,7 @@ struct lu_object *lu_object_find_at(const struct lu_env *env,
                 * lu_object_find_try() already added waiter into the
                 * wait queue.
                 */
-               waitq_wait(&wait, TASK_UNINTERRUPTIBLE);
+               schedule();
                bkt = lu_site_bkt_from_fid(dev->ld_site, (void *)f);
                remove_wait_queue(&bkt->lsb_marche_funebre, &wait);
        }
@@ -854,7 +869,7 @@ EXPORT_SYMBOL(lu_device_type_fini);
  * Global list of all sites on this node
  */
 static struct list_head lu_sites;
-static DEFINE_MUTEX(lu_sites_guard);
+static struct rw_semaphore lu_sites_guard;
 
 /**
  * Global environment used by site shrinker.
@@ -868,7 +883,7 @@ struct lu_site_print_arg {
 };
 
 static int
-lu_site_obj_print(cfs_hash_t *hs, cfs_hash_bd_t *bd,
+lu_site_obj_print(struct cfs_hash *hs, struct cfs_hash_bd *bd,
                  struct hlist_node *hnode, void *data)
 {
        struct lu_site_print_arg *arg = (struct lu_site_print_arg *)data;
@@ -911,6 +926,7 @@ static unsigned long lu_htable_order(struct lu_device *top)
 {
        unsigned long cache_size;
        unsigned long bits;
+       unsigned long bits_max = LU_SITE_BITS_MAX;
 
        /*
         * For ZFS based OSDs the cache should be disabled by default.  This
@@ -924,6 +940,9 @@ static unsigned long lu_htable_order(struct lu_device *top)
                return LU_SITE_BITS_MIN;
        }
 
+       if (strcmp(top->ld_type->ldt_name, LUSTRE_VVP_NAME) == 0)
+               bits_max = LU_SITE_BITS_MAX_CL;
+
         /*
          * Calculate hash table size, assuming that we want reasonable
          * performance when 20% of total memory is occupied by cache of
@@ -935,8 +954,8 @@ static unsigned long lu_htable_order(struct lu_device *top)
 
 #if BITS_PER_LONG == 32
         /* limit hashtable size for lowmem systems to low RAM */
-       if (cache_size > 1 << (30 - PAGE_CACHE_SHIFT))
-               cache_size = 1 << (30 - PAGE_CACHE_SHIFT) * 3 / 4;
+       if (cache_size > 1 << (30 - PAGE_SHIFT))
+               cache_size = 1 << (30 - PAGE_SHIFT) * 3 / 4;
 #endif
 
         /* clear off unreasonable cache setting. */
@@ -949,15 +968,16 @@ static unsigned long lu_htable_order(struct lu_device *top)
                 lu_cache_percent = LU_CACHE_PERCENT_DEFAULT;
         }
         cache_size = cache_size / 100 * lu_cache_percent *
-               (PAGE_CACHE_SIZE / 1024);
+               (PAGE_SIZE / 1024);
 
         for (bits = 1; (1 << bits) < cache_size; ++bits) {
                 ;
         }
-        return bits;
+
+       return clamp_t(typeof(bits), bits, LU_SITE_BITS_MIN, bits_max);
 }
 
-static unsigned lu_obj_hop_hash(cfs_hash_t *hs,
+static unsigned lu_obj_hop_hash(struct cfs_hash *hs,
                                const void *key, unsigned mask)
 {
        struct lu_fid  *fid = (struct lu_fid *)key;
@@ -997,7 +1017,7 @@ static int lu_obj_hop_keycmp(const void *key, struct hlist_node *hnode)
        return lu_fid_eq(&h->loh_fid, (struct lu_fid *)key);
 }
 
-static void lu_obj_hop_get(cfs_hash_t *hs, struct hlist_node *hnode)
+static void lu_obj_hop_get(struct cfs_hash *hs, struct hlist_node *hnode)
 {
        struct lu_object_header *h;
 
@@ -1005,12 +1025,12 @@ static void lu_obj_hop_get(cfs_hash_t *hs, struct hlist_node *hnode)
        atomic_inc(&h->loh_ref);
 }
 
-static void lu_obj_hop_put_locked(cfs_hash_t *hs, struct hlist_node *hnode)
+static void lu_obj_hop_put_locked(struct cfs_hash *hs, struct hlist_node *hnode)
 {
         LBUG(); /* we should never called it */
 }
 
-static cfs_hash_ops_t lu_site_hash_ops = {
+static struct cfs_hash_ops lu_site_hash_ops = {
         .hs_hash        = lu_obj_hop_hash,
         .hs_key         = lu_obj_hop_key,
         .hs_keycmp      = lu_obj_hop_keycmp,
@@ -1042,18 +1062,26 @@ EXPORT_SYMBOL(lu_dev_del_linkage);
 int lu_site_init(struct lu_site *s, struct lu_device *top)
 {
        struct lu_site_bkt_data *bkt;
-       cfs_hash_bd_t bd;
+       struct cfs_hash_bd bd;
        char name[16];
        unsigned long bits;
        unsigned int i;
+       int rc;
        ENTRY;
 
        memset(s, 0, sizeof *s);
        mutex_init(&s->ls_purge_mutex);
-       bits = lu_htable_order(top);
+
+#ifdef HAVE_PERCPU_COUNTER_INIT_GFP_FLAG
+       rc = percpu_counter_init(&s->ls_lru_len_counter, 0, GFP_NOFS);
+#else
+       rc = percpu_counter_init(&s->ls_lru_len_counter, 0);
+#endif
+       if (rc)
+               return -ENOMEM;
+
        snprintf(name, sizeof(name), "lu_site_%s", top->ld_type->ldt_name);
-       for (bits = clamp_t(typeof(bits), bits,
-                           LU_SITE_BITS_MIN, LU_SITE_BITS_MAX);
+       for (bits = lu_htable_order(top);
             bits >= LU_SITE_BITS_MIN; bits--) {
                s->ls_obj_hash = cfs_hash_create(name, bits, bits,
                                                 bits - LU_SITE_BKT_BITS,
@@ -1119,9 +1147,11 @@ EXPORT_SYMBOL(lu_site_init);
  */
 void lu_site_fini(struct lu_site *s)
 {
-       mutex_lock(&lu_sites_guard);
+       down_write(&lu_sites_guard);
        list_del_init(&s->ls_linkage);
-       mutex_unlock(&lu_sites_guard);
+       up_write(&lu_sites_guard);
+
+       percpu_counter_destroy(&s->ls_lru_len_counter);
 
         if (s->ls_obj_hash != NULL) {
                 cfs_hash_putref(s->ls_obj_hash);
@@ -1146,11 +1176,11 @@ EXPORT_SYMBOL(lu_site_fini);
 int lu_site_init_finish(struct lu_site *s)
 {
         int result;
-       mutex_lock(&lu_sites_guard);
+       down_write(&lu_sites_guard);
         result = lu_context_refill(&lu_shrink_env.le_ctx);
         if (result == 0)
                list_add(&s->ls_linkage, &lu_sites);
-       mutex_unlock(&lu_sites_guard);
+       up_write(&lu_sites_guard);
         return result;
 }
 EXPORT_SYMBOL(lu_site_init_finish);
@@ -1364,7 +1394,8 @@ enum {
 
 static struct lu_context_key *lu_keys[LU_CONTEXT_KEY_NR] = { NULL, };
 
-static DEFINE_SPINLOCK(lu_keys_guard);
+DEFINE_RWLOCK(lu_keys_guard);
+static atomic_t lu_key_initing_cnt = ATOMIC_INIT(0);
 
 /**
  * Global counter incremented whenever key is registered, unregistered,
@@ -1388,7 +1419,7 @@ int lu_context_key_register(struct lu_context_key *key)
         LASSERT(key->lct_owner != NULL);
 
         result = -ENFILE;
-       spin_lock(&lu_keys_guard);
+       write_lock(&lu_keys_guard);
         for (i = 0; i < ARRAY_SIZE(lu_keys); ++i) {
                 if (lu_keys[i] == NULL) {
                         key->lct_index = i;
@@ -1400,7 +1431,7 @@ int lu_context_key_register(struct lu_context_key *key)
                         break;
                 }
         }
-       spin_unlock(&lu_keys_guard);
+       write_unlock(&lu_keys_guard);
        return result;
 }
 EXPORT_SYMBOL(lu_context_key_register);
@@ -1439,13 +1470,26 @@ void lu_context_key_degister(struct lu_context_key *key)
        lu_context_key_quiesce(key);
 
        ++key_set_version;
-       spin_lock(&lu_keys_guard);
+       write_lock(&lu_keys_guard);
        key_fini(&lu_shrink_env.le_ctx, key->lct_index);
+
+       /**
+        * Wait until all transient contexts referencing this key have
+        * run lu_context_key::lct_fini() method.
+        */
+       while (atomic_read(&key->lct_used) > 1) {
+               write_unlock(&lu_keys_guard);
+               CDEBUG(D_INFO, "lu_context_key_degister: \"%s\" %p, %d\n",
+                      key->lct_owner ? key->lct_owner->name : "", key,
+                      atomic_read(&key->lct_used));
+               schedule();
+               write_lock(&lu_keys_guard);
+       }
        if (lu_keys[key->lct_index]) {
                lu_keys[key->lct_index] = NULL;
                lu_ref_fini(&key->lct_reference);
        }
-       spin_unlock(&lu_keys_guard);
+       write_unlock(&lu_keys_guard);
 
        LASSERTF(atomic_read(&key->lct_used) == 1,
                 "key has instances: %d\n",
@@ -1559,23 +1603,34 @@ static struct list_head lu_context_remembered;
  */
 void lu_context_key_quiesce(struct lu_context_key *key)
 {
-        struct lu_context *ctx;
-        extern unsigned cl_env_cache_purge(unsigned nr);
+       struct lu_context *ctx;
 
-        if (!(key->lct_tags & LCT_QUIESCENT)) {
-                /*
-                 * XXX layering violation.
-                 */
-                cl_env_cache_purge(~0);
-                key->lct_tags |= LCT_QUIESCENT;
+       if (!(key->lct_tags & LCT_QUIESCENT)) {
                 /*
                  * XXX memory barrier has to go here.
                  */
-               spin_lock(&lu_keys_guard);
+               write_lock(&lu_keys_guard);
+               key->lct_tags |= LCT_QUIESCENT;
+
+               /**
+                * Wait until all lu_context_key::lct_init() methods
+                * have completed.
+                */
+               while (atomic_read(&lu_key_initing_cnt) > 0) {
+                       write_unlock(&lu_keys_guard);
+                       CDEBUG(D_INFO, "lu_context_key_quiesce: \"%s\""
+                              " %p, %d (%d)\n",
+                              key->lct_owner ? key->lct_owner->name : "",
+                              key, atomic_read(&key->lct_used),
+                              atomic_read(&lu_key_initing_cnt));
+                       schedule();
+                       write_lock(&lu_keys_guard);
+               }
+
                list_for_each_entry(ctx, &lu_context_remembered,
                                    lc_remember)
                        key_fini(ctx, key->lct_index);
-               spin_unlock(&lu_keys_guard);
+               write_unlock(&lu_keys_guard);
                ++key_set_version;
        }
 }
@@ -1604,6 +1659,19 @@ static int keys_fill(struct lu_context *ctx)
 {
        unsigned int i;
 
+       /*
+        * A serialisation with lu_context_key_quiesce() is needed, but some
+        * "key->lct_init()" are calling kernel memory allocation routine and
+        * can't be called while holding a spin_lock.
+        * "lu_keys_guard" is held while incrementing "lu_key_initing_cnt"
+        * to ensure the start of the serialisation.
+        * An atomic_t variable is still used, in order not to reacquire the
+        * lock when decrementing the counter.
+        */
+       read_lock(&lu_keys_guard);
+       atomic_inc(&lu_key_initing_cnt);
+       read_unlock(&lu_keys_guard);
+
         LINVRNT(ctx->lc_value != NULL);
         for (i = 0; i < ARRAY_SIZE(lu_keys); ++i) {
                 struct lu_context_key *key;
@@ -1621,13 +1689,19 @@ static int keys_fill(struct lu_context *ctx)
                         LINVRNT(key->lct_init != NULL);
                         LINVRNT(key->lct_index == i);
 
-                        value = key->lct_init(ctx, key);
-                        if (unlikely(IS_ERR(value)))
-                                return PTR_ERR(value);
-
                        LASSERT(key->lct_owner != NULL);
-                       if (!(ctx->lc_tags & LCT_NOREF))
-                               try_module_get(key->lct_owner);
+                       if (!(ctx->lc_tags & LCT_NOREF) &&
+                           try_module_get(key->lct_owner) == 0) {
+                               /* module is unloading, skip this key */
+                               continue;
+                       }
+
+                       value = key->lct_init(ctx, key);
+                       if (unlikely(IS_ERR(value))) {
+                               atomic_dec(&lu_key_initing_cnt);
+                               return PTR_ERR(value);
+                       }
+
                        lu_ref_add_atomic(&key->lct_reference, "ctx", ctx);
                        atomic_inc(&key->lct_used);
                         /*
@@ -1641,6 +1715,7 @@ static int keys_fill(struct lu_context *ctx)
                 }
                 ctx->lc_version = key_set_version;
         }
+       atomic_dec(&lu_key_initing_cnt);
         return 0;
 }
 
@@ -1664,9 +1739,9 @@ int lu_context_init(struct lu_context *ctx, __u32 tags)
        ctx->lc_state = LCS_INITIALIZED;
        ctx->lc_tags = tags;
        if (tags & LCT_REMEMBER) {
-               spin_lock(&lu_keys_guard);
+               write_lock(&lu_keys_guard);
                list_add(&ctx->lc_remember, &lu_context_remembered);
-               spin_unlock(&lu_keys_guard);
+               write_unlock(&lu_keys_guard);
        } else {
                INIT_LIST_HEAD(&ctx->lc_remember);
        }
@@ -1692,10 +1767,10 @@ void lu_context_fini(struct lu_context *ctx)
                keys_fini(ctx);
 
        } else { /* could race with key degister */
-               spin_lock(&lu_keys_guard);
+               write_lock(&lu_keys_guard);
                keys_fini(ctx);
                list_del_init(&ctx->lc_remember);
-               spin_unlock(&lu_keys_guard);
+               write_unlock(&lu_keys_guard);
        }
 }
 EXPORT_SYMBOL(lu_context_fini);
@@ -1720,10 +1795,11 @@ void lu_context_exit(struct lu_context *ctx)
         LINVRNT(ctx->lc_state == LCS_ENTERED);
         ctx->lc_state = LCS_LEFT;
         if (ctx->lc_tags & LCT_HAS_EXIT && ctx->lc_value != NULL) {
+               /* could race with key quiescency */
+               if (ctx->lc_tags & LCT_REMEMBER)
+                       read_lock(&lu_keys_guard);
+
                 for (i = 0; i < ARRAY_SIZE(lu_keys); ++i) {
-                       /* could race with key quiescency */
-                       if (ctx->lc_tags & LCT_REMEMBER)
-                               spin_lock(&lu_keys_guard);
                        if (ctx->lc_value[i] != NULL) {
                                struct lu_context_key *key;
 
@@ -1733,9 +1809,10 @@ void lu_context_exit(struct lu_context *ctx)
                                        key->lct_exit(ctx,
                                                      key, ctx->lc_value[i]);
                        }
-                       if (ctx->lc_tags & LCT_REMEMBER)
-                               spin_unlock(&lu_keys_guard);
                 }
+
+               if (ctx->lc_tags & LCT_REMEMBER)
+                       read_unlock(&lu_keys_guard);
         }
 }
 EXPORT_SYMBOL(lu_context_exit);
@@ -1762,37 +1839,37 @@ __u32 lu_session_tags_default = 0;
 
 void lu_context_tags_update(__u32 tags)
 {
-       spin_lock(&lu_keys_guard);
+       write_lock(&lu_keys_guard);
        lu_context_tags_default |= tags;
        key_set_version++;
-       spin_unlock(&lu_keys_guard);
+       write_unlock(&lu_keys_guard);
 }
 EXPORT_SYMBOL(lu_context_tags_update);
 
 void lu_context_tags_clear(__u32 tags)
 {
-       spin_lock(&lu_keys_guard);
+       write_lock(&lu_keys_guard);
        lu_context_tags_default &= ~tags;
        key_set_version++;
-       spin_unlock(&lu_keys_guard);
+       write_unlock(&lu_keys_guard);
 }
 EXPORT_SYMBOL(lu_context_tags_clear);
 
 void lu_session_tags_update(__u32 tags)
 {
-       spin_lock(&lu_keys_guard);
+       write_lock(&lu_keys_guard);
        lu_session_tags_default |= tags;
        key_set_version++;
-       spin_unlock(&lu_keys_guard);
+       write_unlock(&lu_keys_guard);
 }
 EXPORT_SYMBOL(lu_session_tags_update);
 
 void lu_session_tags_clear(__u32 tags)
 {
-       spin_lock(&lu_keys_guard);
+       write_lock(&lu_keys_guard);
        lu_session_tags_default &= ~tags;
        key_set_version++;
-       spin_unlock(&lu_keys_guard);
+       write_unlock(&lu_keys_guard);
 }
 EXPORT_SYMBOL(lu_session_tags_clear);
 
@@ -1864,10 +1941,10 @@ typedef struct lu_site_stats{
         unsigned        lss_busy;
 } lu_site_stats_t;
 
-static void lu_site_stats_get(cfs_hash_t *hs,
+static void lu_site_stats_get(struct cfs_hash *hs,
                               lu_site_stats_t *stats, int populated)
 {
-       cfs_hash_bd_t bd;
+       struct cfs_hash_bd bd;
        unsigned int  i;
 
         cfs_hash_for_each_bucket(hs, &bd, i) {
@@ -1894,10 +1971,25 @@ static void lu_site_stats_get(cfs_hash_t *hs,
 }
 
 
+/*
+ * lu_cache_shrink_count() returns an approximate number of cached objects
+ * that can be freed by shrink_slab(). A counter, which tracks the
+ * number of items in the site's lru, is maintained in a percpu_counter
+ * for each site. The percpu values are incremented and decremented as
+ * objects are added or removed from the lru. The percpu values are summed
+ * and saved whenever a percpu value exceeds a threshold. Thus the saved,
+ * summed value at any given time may not accurately reflect the current
+ * lru length. But this value is sufficiently accurate for the needs of
+ * a shrinker.
+ *
+ * Using a per cpu counter is a compromise solution to concurrent access:
+ * lu_object_put() can update the counter without locking the site and
+ * lu_cache_shrink_count can sum the counters without locking each
+ * ls_obj_hash bucket.
+ */
 static unsigned long lu_cache_shrink_count(struct shrinker *sk,
                                           struct shrink_control *sc)
 {
-       lu_site_stats_t stats;
        struct lu_site *s;
        struct lu_site *tmp;
        unsigned long cached = 0;
@@ -1905,16 +1997,15 @@ static unsigned long lu_cache_shrink_count(struct shrinker *sk,
        if (!(sc->gfp_mask & __GFP_FS))
                return 0;
 
-       mutex_lock(&lu_sites_guard);
-       list_for_each_entry_safe(s, tmp, &lu_sites, ls_linkage) {
-               memset(&stats, 0, sizeof(stats));
-               lu_site_stats_get(s->ls_obj_hash, &stats, 0);
-               cached += stats.lss_total - stats.lss_busy;
-       }
-       mutex_unlock(&lu_sites_guard);
+       down_read(&lu_sites_guard);
+       list_for_each_entry_safe(s, tmp, &lu_sites, ls_linkage)
+               cached += percpu_counter_read_positive(&s->ls_lru_len_counter);
+       up_read(&lu_sites_guard);
 
        cached = (cached / 100) * sysctl_vfs_cache_pressure;
-       CDEBUG(D_INODE, "%ld objects cached\n", cached);
+       CDEBUG(D_INODE, "%ld objects cached, cache pressure %d\n",
+              cached, sysctl_vfs_cache_pressure);
+
        return cached;
 }
 
@@ -1940,7 +2031,7 @@ static unsigned long lu_cache_shrink_scan(struct shrinker *sk,
                 */
                return SHRINK_STOP;
 
-       mutex_lock(&lu_sites_guard);
+       down_write(&lu_sites_guard);
        list_for_each_entry_safe(s, tmp, &lu_sites, ls_linkage) {
                remain = lu_site_purge(&lu_shrink_env, s, remain);
                /*
@@ -1950,7 +2041,7 @@ static unsigned long lu_cache_shrink_scan(struct shrinker *sk,
                list_move_tail(&s->ls_linkage, &splice);
        }
        list_splice(&splice, lu_sites.prev);
-       mutex_unlock(&lu_sites_guard);
+       up_write(&lu_sites_guard);
 
        return sc->nr_to_scan - remain;
 }
@@ -1971,7 +2062,7 @@ static unsigned long lu_cache_shrink_scan(struct shrinker *sk,
  * is safe to take the lu_sites_guard lock.
  *
  * Ideally we should accurately return the remaining number of cached
- * objects without taking the  lu_sites_guard lock, but this is not
+ * objects without taking the lu_sites_guard lock, but this is not
  * possible in the current implementation.
  */
 static int lu_cache_shrink(SHRINKER_ARGS(sc, nr_to_scan, gfp_mask))
@@ -1988,11 +2079,10 @@ static int lu_cache_shrink(SHRINKER_ARGS(sc, nr_to_scan, gfp_mask))
 
        CDEBUG(D_INODE, "Shrink %lu objects\n", scv.nr_to_scan);
 
-       lu_cache_shrink_scan(shrinker, &scv);
+       if (scv.nr_to_scan != 0)
+               lu_cache_shrink_scan(shrinker, &scv);
 
        cached = lu_cache_shrink_count(shrinker, &scv);
-       if (scv.nr_to_scan == 0)
-               CDEBUG(D_INODE, "%d objects cached\n", cached);
        return cached;
 }
 
@@ -2061,6 +2151,7 @@ int lu_global_init(void)
        INIT_LIST_HEAD(&lu_device_types);
        INIT_LIST_HEAD(&lu_context_remembered);
        INIT_LIST_HEAD(&lu_sites);
+       init_rwsem(&lu_sites_guard);
 
         result = lu_ref_global_init();
         if (result != 0)
@@ -2076,9 +2167,9 @@ int lu_global_init(void)
          * conservatively. This should not be too bad, because this
          * environment is global.
          */
-       mutex_lock(&lu_sites_guard);
+       down_write(&lu_sites_guard);
         result = lu_env_init(&lu_shrink_env, LCT_SHRINKER);
-       mutex_unlock(&lu_sites_guard);
+       up_write(&lu_sites_guard);
         if (result != 0)
                 return result;
 
@@ -2110,9 +2201,9 @@ void lu_global_fini(void)
          * Tear shrinker environment down _after_ de-registering
          * lu_global_key, because the latter has a value in the former.
          */
-       mutex_lock(&lu_sites_guard);
+       down_write(&lu_sites_guard);
         lu_env_fini(&lu_shrink_env);
-       mutex_unlock(&lu_sites_guard);
+       up_write(&lu_sites_guard);
 
         lu_ref_global_fini();
 }
@@ -2120,12 +2211,12 @@ void lu_global_fini(void)
 static __u32 ls_stats_read(struct lprocfs_stats *stats, int idx)
 {
 #ifdef CONFIG_PROC_FS
-        struct lprocfs_counter ret;
+       struct lprocfs_counter ret;
 
-        lprocfs_stats_collect(stats, idx, &ret);
-        return (__u32)ret.lc_count;
+       lprocfs_stats_collect(stats, idx, &ret);
+       return (__u32)ret.lc_count;
 #else
-        return 0;
+       return 0;
 #endif
 }
 
@@ -2140,42 +2231,22 @@ int lu_site_stats_seq_print(const struct lu_site *s, struct seq_file *m)
        memset(&stats, 0, sizeof(stats));
        lu_site_stats_get(s->ls_obj_hash, &stats, 1);
 
-       return seq_printf(m, "%d/%d %d/%d %d %d %d %d %d %d %d\n",
-                         stats.lss_busy,
-                         stats.lss_total,
-                         stats.lss_populated,
-                         CFS_HASH_NHLIST(s->ls_obj_hash),
-                         stats.lss_max_search,
-                         ls_stats_read(s->ls_stats, LU_SS_CREATED),
-                         ls_stats_read(s->ls_stats, LU_SS_CACHE_HIT),
-                         ls_stats_read(s->ls_stats, LU_SS_CACHE_MISS),
-                         ls_stats_read(s->ls_stats, LU_SS_CACHE_RACE),
-                         ls_stats_read(s->ls_stats, LU_SS_CACHE_DEATH_RACE),
-                         ls_stats_read(s->ls_stats, LU_SS_LRU_PURGED));
+       seq_printf(m, "%d/%d %d/%d %d %d %d %d %d %d %d\n",
+                  stats.lss_busy,
+                  stats.lss_total,
+                  stats.lss_populated,
+                  CFS_HASH_NHLIST(s->ls_obj_hash),
+                  stats.lss_max_search,
+                  ls_stats_read(s->ls_stats, LU_SS_CREATED),
+                  ls_stats_read(s->ls_stats, LU_SS_CACHE_HIT),
+                  ls_stats_read(s->ls_stats, LU_SS_CACHE_MISS),
+                  ls_stats_read(s->ls_stats, LU_SS_CACHE_RACE),
+                  ls_stats_read(s->ls_stats, LU_SS_CACHE_DEATH_RACE),
+                  ls_stats_read(s->ls_stats, LU_SS_LRU_PURGED));
+       return 0;
 }
 EXPORT_SYMBOL(lu_site_stats_seq_print);
 
-int lu_site_stats_print(const struct lu_site *s, char *page, int count)
-{
-        lu_site_stats_t stats;
-
-        memset(&stats, 0, sizeof(stats));
-        lu_site_stats_get(s->ls_obj_hash, &stats, 1);
-
-        return snprintf(page, count, "%d/%d %d/%d %d %d %d %d %d %d %d\n",
-                        stats.lss_busy,
-                        stats.lss_total,
-                        stats.lss_populated,
-                        CFS_HASH_NHLIST(s->ls_obj_hash),
-                        stats.lss_max_search,
-                        ls_stats_read(s->ls_stats, LU_SS_CREATED),
-                        ls_stats_read(s->ls_stats, LU_SS_CACHE_HIT),
-                        ls_stats_read(s->ls_stats, LU_SS_CACHE_MISS),
-                        ls_stats_read(s->ls_stats, LU_SS_CACHE_RACE),
-                        ls_stats_read(s->ls_stats, LU_SS_CACHE_DEATH_RACE),
-                        ls_stats_read(s->ls_stats, LU_SS_LRU_PURGED));
-}
-
 /**
  * Helper function to initialize a number of kmem slab caches at once.
  */
@@ -2223,19 +2294,24 @@ void lu_object_assign_fid(const struct lu_env *env, struct lu_object *o,
 {
        struct lu_site          *s = o->lo_dev->ld_site;
        struct lu_fid           *old = &o->lo_header->loh_fid;
-       struct lu_object        *shadow;
-       wait_queue_t             waiter;
-       cfs_hash_t              *hs;
-       cfs_hash_bd_t            bd;
-       __u64                    version = 0;
+       struct cfs_hash         *hs;
+       struct cfs_hash_bd       bd;
 
        LASSERT(fid_is_zero(old));
 
+       /* supposed to be unique */
        hs = s->ls_obj_hash;
        cfs_hash_bd_get_and_lock(hs, (void *)fid, &bd, 1);
-       shadow = htable_lookup(s, &bd, fid, &waiter, &version);
-       /* supposed to be unique */
-       LASSERT(IS_ERR(shadow) && PTR_ERR(shadow) == -ENOENT);
+#ifdef CONFIG_LUSTRE_DEBUG_EXPENSIVE_CHECK
+       {
+               __u64                    version = 0;
+               wait_queue_t             waiter;
+               struct lu_object        *shadow;
+               shadow = htable_lookup(s, &bd, fid, &waiter, &version);
+               /* supposed to be unique */
+               LASSERT(IS_ERR(shadow) && PTR_ERR(shadow) == -ENOENT);
+       }
+#endif
        *old = *fid;
        cfs_hash_bd_add_locked(hs, &bd, &o->lo_header->loh_hash);
        cfs_hash_bd_unlock(hs, &bd, 1);