LU-16695 llite: switch to ki_flags from f_flags

[fs/lustre-release.git] / lustre / llite / rw.c

/*
 * GPL HEADER START
 *
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 only,
 * as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License version 2 for more details (a copy is included
 * in the LICENSE file that accompanied this code).
 *
 * You should have received a copy of the GNU General Public License
 * version 2 along with this program; If not, see
 * http://www.gnu.org/licenses/gpl-2.0.html
 *
 * GPL HEADER END
 */
/*
 * Copyright (c) 2002, 2010, Oracle and/or its affiliates. All rights reserved.
 * Use is subject to license terms.
 *
 * Copyright (c) 2011, 2017, Intel Corporation.
 */
/*
 * This file is part of Lustre, http://www.lustre.org/
 *
 * lustre/llite/rw.c
 *
 * Lustre Lite I/O page cache routines shared by different kernel revs
 */

#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/string.h>
#include <linux/stat.h>
#include <linux/errno.h>
#include <linux/unistd.h>
#include <linux/writeback.h>
#include <asm/uaccess.h>

#include <linux/fs.h>
#include <linux/file.h>
#include <linux/stat.h>
#include <asm/uaccess.h>
#include <linux/mm.h>
#include <linux/pagemap.h>
/* current_is_kswapd() */
#include <linux/swap.h>
#include <linux/task_io_accounting_ops.h>

#define DEBUG_SUBSYSTEM S_LLITE

#include <obd_cksum.h>
#include "llite_internal.h"
#include <lustre_compat.h>

static void ll_ra_stats_inc_sbi(struct ll_sb_info *sbi, enum ra_stat which);

/**
 * Get readahead pages from the filesystem readahead pool of the client for a
 * thread.
 *
 * /param sbi superblock for filesystem readahead state ll_ra_info
 * /param ria per-thread readahead state
 * /param pages number of pages requested for readahead for the thread.
 *
 * WARNING: This algorithm is used to reduce contention on sbi->ll_lock.
 * It should work well if the ra_max_pages is much greater than the single
 * file's read-ahead window, and not too many threads contending for
 * these readahead pages.
 *
 * TODO: There may be a 'global sync problem' if many threads are trying
 * to get an ra budget that is larger than the remaining readahead pages
 * and reach here at exactly the same time. They will compute /a ret to
 * consume the remaining pages, but will fail at atomic_add_return() and
 * get a zero ra window, although there is still ra space remaining. - Jay */

static unsigned long ll_ra_count_get(struct ll_sb_info *sbi,
                                     struct ra_io_arg *ria,
                                     unsigned long pages,
                                     unsigned long pages_min)
{
        struct ll_ra_info *ra = &sbi->ll_ra_info;
        long ret;

        ENTRY;

        WARN_ON_ONCE(pages_min > pages);
        /**
         * Don't try readahead aggresively if we are limited
         * LRU pages, otherwise, it could cause deadlock.
         */
        pages = min(sbi->ll_cache->ccc_lru_max >> 2, pages);
        /**
         * if this happen, we reserve more pages than needed,
         * this will make us leak @ra_cur_pages, because
         * ll_ra_count_put() acutally freed @pages.
         */
        if (unlikely(pages_min > pages))
                pages_min = pages;

        /*
         * If read-ahead pages left are less than 1M, do not do read-ahead,
         * otherwise it will form small read RPC(< 1M), which hurt server
         * performance a lot.
         */
        ret = min(ra->ra_max_pages - atomic_read(&ra->ra_cur_pages),
                  pages);
        if (ret < 0 || ret < min_t(long, PTLRPC_MAX_BRW_PAGES, pages))
                GOTO(out, ret = 0);

        if (atomic_add_return(ret, &ra->ra_cur_pages) > ra->ra_max_pages) {
                atomic_sub(ret, &ra->ra_cur_pages);
                ret = 0;
        }

out:
        if (ret < pages_min) {
                /* override ra limit for maximum performance */
                atomic_add(pages_min - ret, &ra->ra_cur_pages);
                ret = pages_min;
        }
        RETURN(ret);
}

void ll_ra_count_put(struct ll_sb_info *sbi, unsigned long pages)
{
        struct ll_ra_info *ra = &sbi->ll_ra_info;
        atomic_sub(pages, &ra->ra_cur_pages);
}

static void ll_ra_stats_inc_sbi(struct ll_sb_info *sbi, enum ra_stat which)
{
        LASSERTF(which < _NR_RA_STAT, "which: %u\n", which);
        lprocfs_counter_incr(sbi->ll_ra_stats, which);
}

static inline bool ll_readahead_enabled(struct ll_sb_info *sbi)
{
        return sbi->ll_ra_info.ra_max_pages_per_file > 0 &&
                sbi->ll_ra_info.ra_max_pages > 0;
}

void ll_ra_stats_inc(struct inode *inode, enum ra_stat which)
{
        struct ll_sb_info *sbi = ll_i2sbi(inode);

        ll_ra_stats_inc_sbi(sbi, which);
}

static void ll_ra_stats_add(struct inode *inode, enum ra_stat which, long count)
{
        struct ll_sb_info *sbi = ll_i2sbi(inode);

        LASSERTF(which < _NR_RA_STAT, "which: %u\n", which);
        lprocfs_counter_add(sbi->ll_ra_stats, which, count);
}

#define RAS_CDEBUG(ras) \
        CDEBUG(D_READA,                                                      \
               "lre %llu cr %lu cb %llu wsi %lu wp %lu nra %lu rpc %lu "     \
               "r %lu csr %lu so %llu sb %llu sl %llu lr %lu\n",             \
               ras->ras_last_read_end_bytes, ras->ras_consecutive_requests,  \
               ras->ras_consecutive_bytes, ras->ras_window_start_idx,        \
               ras->ras_window_pages, ras->ras_next_readahead_idx,           \
               ras->ras_rpc_pages, ras->ras_requests,                        \
               ras->ras_consecutive_stride_requests, ras->ras_stride_offset, \
               ras->ras_stride_bytes, ras->ras_stride_length,                \
               ras->ras_async_last_readpage_idx)

static bool pos_in_window(loff_t pos, loff_t point,
                          unsigned long before, unsigned long after)
{
        loff_t start = point - before;
        loff_t end = point + after;

        if (start > point)
                start = 0;
        if (end < point)
                end = ~0;

        return start <= pos && pos <= end;
}

enum ll_ra_page_hint {
        MAYNEED = 0, /* this page possibly accessed soon */
        WILLNEED /* this page is gurateed to be needed */
};

/**
 * Initiates read-ahead of a page with given index.
 *
 * \retval +ve: page was already uptodate so it will be skipped
 *              from being added;
 * \retval -ve: page wasn't added to \a queue for error;
 * \retval   0: page was added into \a queue for read ahead.
 */
static int ll_read_ahead_page(const struct lu_env *env, struct cl_io *io,
                              struct cl_page_list *queue, pgoff_t index,
                              enum ll_ra_page_hint hint)
{
        struct cl_object *clob  = io->ci_obj;
        struct inode     *inode = vvp_object_inode(clob);
        struct page      *vmpage = NULL;
        struct cl_page   *cp;
        enum ra_stat      which = _NR_RA_STAT; /* keep gcc happy */
        int               rc    = 0;
        const char       *msg   = NULL;

        ENTRY;

        switch (hint) {
        case MAYNEED:
                /*
                 * We need __GFP_NORETRY here for read-ahead page, otherwise
                 * the process will fail with OOM killed due to memcg limit.
                 * See @readahead_gfp_mask for an example.
                 */
                vmpage = pagecache_get_page(inode->i_mapping, index,
                                            FGP_LOCK | FGP_CREAT |
                                            FGP_NOFS | FGP_NOWAIT,
                                            mapping_gfp_mask(inode->i_mapping) |
                                            __GFP_NORETRY | __GFP_NOWARN);
                if (vmpage == NULL) {
                        which = RA_STAT_FAILED_GRAB_PAGE;
                        msg   = "g_c_p_n failed";
                        GOTO(out, rc = -EBUSY);
                }
                break;
        case WILLNEED:
                vmpage = find_or_create_page(inode->i_mapping, index,
                                             GFP_NOFS);
                if (vmpage == NULL)
                        GOTO(out, rc = -ENOMEM);
                break;
        default:
                /* should not come here */
                GOTO(out, rc = -EINVAL);
        }

        /* Check if vmpage was truncated or reclaimed */
        if (vmpage->mapping != inode->i_mapping) {
                which = RA_STAT_WRONG_GRAB_PAGE;
                msg   = "g_c_p_n returned invalid page";
                GOTO(out, rc = -EBUSY);
        }

        cp = cl_page_find(env, clob, vmpage->index, vmpage, CPT_CACHEABLE);
        if (IS_ERR(cp)) {
                which = RA_STAT_FAILED_GRAB_PAGE;
                msg   = "cl_page_find failed";
                GOTO(out, rc = PTR_ERR(cp));
        }

        lu_ref_add(&cp->cp_reference, "ra", current);
        cl_page_assume(env, io, cp);

        if (!cp->cp_defer_uptodate && !PageUptodate(vmpage)) {
                if (hint == MAYNEED) {
                        cp->cp_defer_uptodate = 1;
                        cp->cp_ra_used = 0;
                }

                cl_page_list_add(queue, cp, true);
        } else {
                /* skip completed pages */
                cl_page_unassume(env, io, cp);
                /* This page is already uptodate, returning a positive number
                 * to tell the callers about this */
                rc = 1;
        }

        lu_ref_del(&cp->cp_reference, "ra", current);
        cl_page_put(env, cp);

out:
        if (vmpage != NULL) {
                if (rc != 0)
                        unlock_page(vmpage);
                put_page(vmpage);
        }
        if (msg != NULL && hint == MAYNEED) {
                ll_ra_stats_inc(inode, which);
                CDEBUG(D_READA, "%s\n", msg);

        }

        RETURN(rc);
}

#define RIA_DEBUG(ria)                                                  \
        CDEBUG(D_READA, "rs %lu re %lu ro %llu rl %llu rb %llu\n",      \
               ria->ria_start_idx, ria->ria_end_idx, ria->ria_stoff,    \
               ria->ria_length, ria->ria_bytes)

static inline int stride_io_mode(struct ll_readahead_state *ras)
{
        return ras->ras_consecutive_stride_requests > 1;
}

/* The function calculates how many bytes will be read in
 * [off, off + length], in such stride IO area,
 * stride_offset = st_off, stride_lengh = st_len,
 * stride_bytes = st_bytes
 *
 *   |------------------|*****|------------------|*****|------------|*****|....
 * st_off
 *   |--- st_bytes     ---|
 *   |-----     st_len   -----|
 *
 *              How many bytes it should read in such pattern
 *              |-------------------------------------------------------------|
 *              off
 *              |<------                  length                      ------->|
 *
 *          =   |<----->|  +  |-------------------------------------| +   |---|
 *             start_left                 st_bytes * i                 end_left
 */
static loff_t stride_byte_count(loff_t st_off, loff_t st_len, loff_t st_bytes,
                                loff_t off, loff_t length)
{
        u64 start = off > st_off ? off - st_off : 0;
        u64 end = off + length > st_off ? off + length - st_off : 0;
        u64 start_left;
        u64 end_left;
        u64 bytes_count;

        if (st_len == 0 || length == 0 || end == 0)
                return length;

        start = div64_u64_rem(start, st_len, &start_left);
        if (start_left < st_bytes)
                start_left = st_bytes - start_left;
        else
                start_left = 0;

        end = div64_u64_rem(end, st_len, &end_left);
        if (end_left > st_bytes)
                end_left = st_bytes;

        CDEBUG(D_READA, "start %llu, end %llu start_left %llu end_left %llu\n",
               start, end, start_left, end_left);

        if (start == end)
                bytes_count = end_left - (st_bytes - start_left);
        else
                bytes_count = start_left +
                        st_bytes * (end - start - 1) + end_left;

        CDEBUG(D_READA,
               "st_off %llu, st_len %llu st_bytes %llu off %llu length %llu bytescount %llu\n",
               st_off, st_len, st_bytes, off, length, bytes_count);

        return bytes_count;
}

static unsigned long ria_page_count(struct ra_io_arg *ria)
{
        loff_t length_bytes = ria->ria_end_idx >= ria->ria_start_idx ?
                (loff_t)(ria->ria_end_idx -
                         ria->ria_start_idx + 1) << PAGE_SHIFT : 0;
        loff_t bytes_count;

        if (ria->ria_length > ria->ria_bytes && ria->ria_bytes &&
            (ria->ria_length & ~PAGE_MASK || ria->ria_bytes & ~PAGE_MASK ||
             ria->ria_stoff & ~PAGE_MASK)) {
                /* Over-estimate un-aligned page stride read */
                unsigned long pg_count = ((ria->ria_bytes +
                                           PAGE_SIZE - 1) >> PAGE_SHIFT) + 1;
                pg_count *= length_bytes / ria->ria_length + 1;

                return pg_count;
        }
        bytes_count = stride_byte_count(ria->ria_stoff, ria->ria_length,
                                        ria->ria_bytes,
                                        (loff_t)ria->ria_start_idx<<PAGE_SHIFT,
                                        length_bytes);
        return (bytes_count + PAGE_SIZE - 1) >> PAGE_SHIFT;
}

static pgoff_t ras_align(struct ll_readahead_state *ras, pgoff_t index)
{
        unsigned opt_size = min(ras->ras_window_pages, ras->ras_rpc_pages);

        if (opt_size == 0)
                opt_size = 1;
        return index - (index % opt_size);
}

/* Check whether the index is in the defined ra-window */
static bool ras_inside_ra_window(pgoff_t idx, struct ra_io_arg *ria)
{
        loff_t pos = (loff_t)idx << PAGE_SHIFT;

        /* If ria_length == ria_bytes, it means non-stride I/O mode,
         * idx should always inside read-ahead window in this case
         * For stride I/O mode, just check whether the idx is inside
         * the ria_bytes.
         */
        if (ria->ria_length == 0 || ria->ria_length == ria->ria_bytes)
                return true;

        if (pos >= ria->ria_stoff) {
                u64 offset;

                div64_u64_rem(pos - ria->ria_stoff, ria->ria_length, &offset);

                if (offset < ria->ria_bytes ||
                    (ria->ria_length - offset) < PAGE_SIZE)
                        return true;
        } else if (pos + PAGE_SIZE > ria->ria_stoff) {
                return true;
        }

        return false;
}

static unsigned long
ll_read_ahead_pages(const struct lu_env *env, struct cl_io *io,
                    struct cl_page_list *queue, struct ll_readahead_state *ras,
                    struct ra_io_arg *ria, pgoff_t *ra_end, pgoff_t skip_index)
{
        struct cl_read_ahead ra = { 0 };
        /* busy page count is per stride */
        int rc = 0, count = 0, busy_page_count = 0;
        pgoff_t page_idx;

        LASSERT(ria != NULL);
        RIA_DEBUG(ria);

        for (page_idx = ria->ria_start_idx;
             page_idx <= ria->ria_end_idx && ria->ria_reserved > 0;
             page_idx++) {
                if (skip_index && page_idx == skip_index)
                        continue;
                if (ras_inside_ra_window(page_idx, ria)) {
                        if (ra.cra_end_idx == 0 || ra.cra_end_idx < page_idx) {
                                pgoff_t end_idx;

                                /*
                                 * Do not shrink ria_end_idx at any case until
                                 * the minimum end of current read is covered.
                                 *
                                 * Do not extend read lock accross stripe if
                                 * lock contention detected.
                                 */
                                if (ra.cra_contention &&
                                    page_idx > ria->ria_end_idx_min) {
                                        ria->ria_end_idx = *ra_end;
                                        break;
                                }

                                cl_read_ahead_release(env, &ra);

                                rc = cl_io_read_ahead(env, io, page_idx, &ra);
                                if (rc < 0)
                                        break;

                                 /*
                                  * Only shrink ria_end_idx if the matched
                                  * LDLM lock doesn't cover more.
                                  */
                                if (page_idx > ra.cra_end_idx) {
                                        ria->ria_end_idx = ra.cra_end_idx;
                                        break;
                                }

                                CDEBUG(D_READA, "idx: %lu, ra: %lu, rpc: %lu\n",
                                       page_idx, ra.cra_end_idx,
                                       ra.cra_rpc_pages);
                                LASSERTF(ra.cra_end_idx >= page_idx,
                                         "object: %p, indcies %lu / %lu\n",
                                         io->ci_obj, ra.cra_end_idx, page_idx);
                                /* update read ahead RPC size.
                                 * NB: it's racy but doesn't matter */
                                if (ras->ras_rpc_pages != ra.cra_rpc_pages &&
                                    ra.cra_rpc_pages > 0)
                                        ras->ras_rpc_pages = ra.cra_rpc_pages;
                                if (!skip_index) {
                                        /* trim it to align with optimal RPC size */
                                        end_idx = ras_align(ras, ria->ria_end_idx + 1);
                                        if (end_idx > 0 && !ria->ria_eof)
                                                ria->ria_end_idx = end_idx - 1;
                                }
                                if (ria->ria_end_idx < ria->ria_end_idx_min)
                                        ria->ria_end_idx = ria->ria_end_idx_min;
                        }
                        if (page_idx > ria->ria_end_idx)
                                break;

                        /* If the page is inside the read-ahead window */
                        rc = ll_read_ahead_page(env, io, queue, page_idx,
                                                MAYNEED);
                        if (rc < 0 && rc != -EBUSY)
                                break;
                        if (rc == -EBUSY) {
                                busy_page_count++;
                                CDEBUG(D_READA,
                                       "skip busy page: %lu\n", page_idx);
                                /* For page unaligned readahead the first
                                 * last pages of each region can be read by
                                 * another reader on the same node, and so
                                 * may be busy. So only stop for > 2 busy
                                 * pages. */
                                if (busy_page_count > 2)
                                        break;
                        }

                        *ra_end = page_idx;
                        /* Only subtract from reserve & count the page if we
                         * really did readahead on that page. */
                        if (rc == 0) {
                                ria->ria_reserved--;
                                count++;
                        }
                } else if (stride_io_mode(ras)) {
                        /* If it is not in the read-ahead window, and it is
                         * read-ahead mode, then check whether it should skip
                         * the stride gap.
                         */
                        loff_t pos = (loff_t)page_idx << PAGE_SHIFT;
                        u64 offset;

                        div64_u64_rem(pos - ria->ria_stoff, ria->ria_length,
                                      &offset);
                        if (offset >= ria->ria_bytes) {
                                pos += (ria->ria_length - offset);
                                if ((pos >> PAGE_SHIFT) >= page_idx + 1)
                                        page_idx = (pos >> PAGE_SHIFT) - 1;
                                busy_page_count = 0;
                                CDEBUG(D_READA,
                                       "Stride: jump %llu pages to %lu\n",
                                       ria->ria_length - offset, page_idx);
                                continue;
                        }
                }
        }

        cl_read_ahead_release(env, &ra);

        if (count)
                ll_ra_stats_add(vvp_object_inode(io->ci_obj),
                                RA_STAT_READAHEAD_PAGES, count);

        return count;
}

static void ll_readahead_work_free(struct ll_readahead_work *work)
{
        fput(work->lrw_file);
        OBD_FREE_PTR(work);
}

static void ll_readahead_handle_work(struct work_struct *wq);
static void ll_readahead_work_add(struct inode *inode,
                                  struct ll_readahead_work *work)
{
        INIT_WORK(&work->lrw_readahead_work, ll_readahead_handle_work);
        queue_work(ll_i2sbi(inode)->ll_ra_info.ll_readahead_wq,
                   &work->lrw_readahead_work);
}

static int ll_readahead_file_kms(const struct lu_env *env,
                                struct cl_io *io, __u64 *kms)
{
        struct cl_object *clob;
        struct inode *inode;
        struct cl_attr *attr = vvp_env_thread_attr(env);
        int ret;

        clob = io->ci_obj;
        inode = vvp_object_inode(clob);

        cl_object_attr_lock(clob);
        ret = cl_object_attr_get(env, clob, attr);
        cl_object_attr_unlock(clob);

        if (ret != 0)
                RETURN(ret);

        *kms = attr->cat_kms;
        return 0;
}

static void ll_readahead_handle_work(struct work_struct *wq)
{
        struct ll_readahead_work *work;
        struct lu_env *env;
        __u16 refcheck;
        struct ra_io_arg *ria;
        struct inode *inode;
        struct ll_file_data *fd;
        struct ll_readahead_state *ras;
        struct cl_io *io;
        struct cl_2queue *queue;
        pgoff_t ra_end_idx = 0;
        unsigned long pages, pages_min = 0;
        struct file *file;
        __u64 kms;
        int rc;
        pgoff_t eof_index;
        struct ll_sb_info *sbi;

        work = container_of(wq, struct ll_readahead_work,
                            lrw_readahead_work);
        fd = work->lrw_file->private_data;
        ras = &fd->fd_ras;
        file = work->lrw_file;
        inode = file_inode(file);
        sbi = ll_i2sbi(inode);

        CDEBUG(D_READA|D_IOTRACE,
               "%s:"DFID": async ra from %lu to %lu triggered by user pid %d\n",
               file_dentry(file)->d_name.name, PFID(ll_inode2fid(inode)),
               work->lrw_start_idx, work->lrw_end_idx, work->lrw_user_pid);

        env = cl_env_alloc(&refcheck, LCT_NOREF);
        if (IS_ERR(env))
                GOTO(out_free_work, rc = PTR_ERR(env));

        io = vvp_env_thread_io(env);
        ll_io_init(io, file, CIT_READ, NULL);

        rc = ll_readahead_file_kms(env, io, &kms);
        if (rc != 0)
                GOTO(out_put_env, rc);

        if (kms == 0) {
                ll_ra_stats_inc(inode, RA_STAT_ZERO_LEN);
                GOTO(out_put_env, rc = 0);
        }

        ria = &ll_env_info(env)->lti_ria;
        memset(ria, 0, sizeof(*ria));

        ria->ria_start_idx = work->lrw_start_idx;
        /* Truncate RA window to end of file */
        eof_index = (pgoff_t)(kms - 1) >> PAGE_SHIFT;
        if (eof_index <= work->lrw_end_idx) {
                work->lrw_end_idx = eof_index;
                ria->ria_eof = true;
        }
        if (work->lrw_end_idx <= work->lrw_start_idx)
                GOTO(out_put_env, rc = 0);

        ria->ria_end_idx = work->lrw_end_idx;
        pages = ria->ria_end_idx - ria->ria_start_idx + 1;
        ria->ria_reserved = ll_ra_count_get(sbi, ria,
                                            ria_page_count(ria), pages_min);

        CDEBUG(D_READA,
               "async reserved pages: %lu/%lu/%lu, ra_cur %d, ra_max %lu\n",
               ria->ria_reserved, pages, pages_min,
               atomic_read(&ll_i2sbi(inode)->ll_ra_info.ra_cur_pages),
               ll_i2sbi(inode)->ll_ra_info.ra_max_pages);

        if (ria->ria_reserved < pages) {
                ll_ra_stats_inc(inode, RA_STAT_MAX_IN_FLIGHT);
                if (PAGES_TO_MiB(ria->ria_reserved) < 1) {
                        ll_ra_count_put(ll_i2sbi(inode), ria->ria_reserved);
                        GOTO(out_put_env, rc = 0);
                }
        }

        rc = cl_io_rw_init(env, io, CIT_READ, ria->ria_start_idx, pages);
        if (rc)
                GOTO(out_put_env, rc);

        /* overwrite jobid inited in vvp_io_init() */
        if (strncmp(ll_i2info(inode)->lli_jobid, work->lrw_jobid,
                    sizeof(work->lrw_jobid)))
                memcpy(ll_i2info(inode)->lli_jobid, work->lrw_jobid,
                       sizeof(work->lrw_jobid));

        vvp_env_io(env)->vui_fd = fd;
        io->ci_state = CIS_LOCKED;
        io->ci_async_readahead = true;
        rc = cl_io_start(env, io);
        if (rc)
                GOTO(out_io_fini, rc);

        queue = &io->ci_queue;
        cl_2queue_init(queue);

        rc = ll_read_ahead_pages(env, io, &queue->c2_qin, ras, ria,
                                 &ra_end_idx, 0);
        if (ria->ria_reserved != 0)
                ll_ra_count_put(ll_i2sbi(inode), ria->ria_reserved);
        if (queue->c2_qin.pl_nr > 0) {
                int count = queue->c2_qin.pl_nr;

                rc = cl_io_submit_rw(env, io, CRT_READ, queue);
                if (rc == 0)
                        task_io_account_read(PAGE_SIZE * count);
        }
        if (ria->ria_end_idx == ra_end_idx && ra_end_idx == (kms >> PAGE_SHIFT))
                ll_ra_stats_inc(inode, RA_STAT_EOF);

        if (ra_end_idx != ria->ria_end_idx)
                ll_ra_stats_inc(inode, RA_STAT_FAILED_REACH_END);

        /* TODO: discard all pages until page reinit route is implemented */
        cl_page_list_discard(env, io, &queue->c2_qin);

        /* Unlock unsent read pages in case of error. */
        cl_page_list_disown(env, &queue->c2_qin);

        cl_2queue_fini(env, queue);
out_io_fini:
        cl_io_end(env, io);
        cl_io_fini(env, io);
out_put_env:
        cl_env_put(env, &refcheck);
out_free_work:
        if (ra_end_idx > 0)
                ll_ra_stats_inc_sbi(ll_i2sbi(inode), RA_STAT_ASYNC);
        atomic_dec(&sbi->ll_ra_info.ra_async_inflight);
        ll_readahead_work_free(work);
}

static int ll_readahead(const struct lu_env *env, struct cl_io *io,
                        struct cl_page_list *queue,
                        struct ll_readahead_state *ras, bool hit,
                        struct file *file, pgoff_t skip_index,
                        pgoff_t *start_idx)
{
        struct vvp_io *vio = vvp_env_io(env);
        struct ll_thread_info *lti = ll_env_info(env);
        unsigned long pages, pages_min = 0;
        pgoff_t ra_end_idx = 0, end_idx = 0;
        struct inode *inode;
        struct ra_io_arg *ria = &lti->lti_ria;
        struct cl_object *clob;
        int ret = 0;
        __u64 kms;
        struct ll_sb_info *sbi;
        struct ll_ra_info *ra;

        ENTRY;

        clob = io->ci_obj;
        inode = vvp_object_inode(clob);
        sbi = ll_i2sbi(inode);
        ra = &sbi->ll_ra_info;

        /**
         * In case we have a limited max_cached_mb, readahead
         * should be stopped if it have run out of all LRU slots.
         */
        if (atomic_read(&ra->ra_cur_pages) >= sbi->ll_cache->ccc_lru_max) {
                ll_ra_stats_inc(inode, RA_STAT_MAX_IN_FLIGHT);
                RETURN(0);
        }

        memset(ria, 0, sizeof(*ria));
        ret = ll_readahead_file_kms(env, io, &kms);
        if (ret != 0)
                RETURN(ret);

        if (kms == 0) {
                ll_ra_stats_inc(inode, RA_STAT_ZERO_LEN);
                RETURN(0);
        }

        spin_lock(&ras->ras_lock);

        /**
         * Note: other thread might rollback the ras_next_readahead_idx,
         * if it can not get the full size of prepared pages, see the
         * end of this function. For stride read ahead, it needs to
         * make sure the offset is no less than ras_stride_offset,
         * so that stride read ahead can work correctly.
         */
        if (stride_io_mode(ras))
                *start_idx = max_t(pgoff_t, ras->ras_next_readahead_idx,
                                  ras->ras_stride_offset >> PAGE_SHIFT);
        else
                *start_idx = ras->ras_next_readahead_idx;

        if (ras->ras_window_pages > 0)
                end_idx = ras->ras_window_start_idx + ras->ras_window_pages - 1;

        if (skip_index)
                end_idx = *start_idx + ras->ras_window_pages - 1;

        /* Enlarge the RA window to encompass the full read */
        if (vio->vui_ra_valid &&
            end_idx < vio->vui_ra_start_idx + vio->vui_ra_pages - 1)
                end_idx = vio->vui_ra_start_idx + vio->vui_ra_pages - 1;

        if (end_idx != 0) {
                pgoff_t eof_index;

                /* Truncate RA window to end of file */
                eof_index = (pgoff_t)((kms - 1) >> PAGE_SHIFT);
                if (eof_index <= end_idx) {
                        end_idx = eof_index;
                        ria->ria_eof = true;
                }
        }
        ria->ria_start_idx = *start_idx;
        ria->ria_end_idx = end_idx;
        /* If stride I/O mode is detected, get stride window*/
        if (stride_io_mode(ras)) {
                ria->ria_stoff = ras->ras_stride_offset;
                ria->ria_length = ras->ras_stride_length;
                ria->ria_bytes = ras->ras_stride_bytes;
        }
        spin_unlock(&ras->ras_lock);

        pages = ria_page_count(ria);

        RAS_CDEBUG(ras);
        CDEBUG(D_READA,
               DFID": ria: %lu/%lu, bead: %lu/%lu, pages %lu, hit: %d\n",
               PFID(lu_object_fid(&clob->co_lu)),
               ria->ria_start_idx, ria->ria_end_idx,
               vio->vui_ra_valid ? vio->vui_ra_start_idx : 0,
               vio->vui_ra_valid ? vio->vui_ra_pages : 0,
               pages, hit);

        if (end_idx == 0) {
                ll_ra_stats_inc(inode, RA_STAT_ZERO_WINDOW);
                RETURN(0);
        }
        if (pages == 0) {
                ll_ra_stats_inc(inode, RA_STAT_ZERO_WINDOW);
                RETURN(0);
        }

        /* at least to extend the readahead window to cover current read */
        if (!hit && vio->vui_ra_valid &&
            vio->vui_ra_start_idx + vio->vui_ra_pages > ria->ria_start_idx) {
                ria->ria_end_idx_min =
                        vio->vui_ra_start_idx + vio->vui_ra_pages - 1;
                pages_min = vio->vui_ra_start_idx + vio->vui_ra_pages -
                                ria->ria_start_idx;
                 /**
                  * For performance reason, exceeding @ra_max_pages
                  * are allowed, but this should be limited with RPC
                  * size in case a large block size read issued. Trim
                  * to RPC boundary.
                  */
                pages_min = min(pages_min, ras->ras_rpc_pages -
                                (ria->ria_start_idx % ras->ras_rpc_pages));
        }

        /* don't over reserved for mmap range read */
        if (skip_index)
                pages_min = 0;
        if (pages_min > pages)
                pages = pages_min;
        ria->ria_reserved = ll_ra_count_get(ll_i2sbi(inode), ria, pages,
                                            pages_min);
        if (ria->ria_reserved < pages)
                ll_ra_stats_inc(inode, RA_STAT_MAX_IN_FLIGHT);

        CDEBUG(D_READA, "reserved pages: %lu/%lu/%lu, ra_cur %d, ra_max %lu\n",
               ria->ria_reserved, pages, pages_min,
               atomic_read(&ll_i2sbi(inode)->ll_ra_info.ra_cur_pages),
               ll_i2sbi(inode)->ll_ra_info.ra_max_pages);

        ret = ll_read_ahead_pages(env, io, queue, ras, ria, &ra_end_idx,
                                  skip_index);
        if (ria->ria_reserved != 0)
                ll_ra_count_put(ll_i2sbi(inode), ria->ria_reserved);

        if (ra_end_idx == end_idx && ra_end_idx == (kms >> PAGE_SHIFT))
                ll_ra_stats_inc(inode, RA_STAT_EOF);

        CDEBUG(D_READA,
               "ra_end_idx = %lu end_idx = %lu stride end = %lu pages = %d\n",
               ra_end_idx, end_idx, ria->ria_end_idx, ret);

        if (ra_end_idx != end_idx)
                ll_ra_stats_inc(inode, RA_STAT_FAILED_REACH_END);
        if (ra_end_idx > 0) {
                /* update the ras so that the next read-ahead tries from
                 * where we left off. */
                spin_lock(&ras->ras_lock);
                ras->ras_next_readahead_idx = ra_end_idx + 1;
                spin_unlock(&ras->ras_lock);
                RAS_CDEBUG(ras);
        }

        RETURN(ret);
}

static int ll_readpages(const struct lu_env *env, struct cl_io *io,
                        struct cl_page_list *queue,
                        pgoff_t start, pgoff_t end)
{
        int ret = 0;
        __u64 kms;
        pgoff_t page_idx;
        int count = 0;

        ENTRY;

        ret = ll_readahead_file_kms(env, io, &kms);
        if (ret != 0)
                RETURN(ret);

        if (kms == 0)
                RETURN(0);

        if (end != 0) {
                unsigned long end_index;

                end_index = (unsigned long)((kms - 1) >> PAGE_SHIFT);
                if (end_index <= end)
                        end = end_index;
        }

        for (page_idx = start; page_idx <= end; page_idx++) {
                ret= ll_read_ahead_page(env, io, queue, page_idx,
                                        WILLNEED);
                if (ret < 0)
                        break;
                else if (ret == 0) /* ret 1 is already uptodate */
                        count++;
        }

        RETURN(count > 0 ? count : ret);
}

static void ras_set_start(struct ll_readahead_state *ras, pgoff_t index)
{
        ras->ras_window_start_idx = ras_align(ras, index);
}

/* called with the ras_lock held or from places where it doesn't matter */
static void ras_reset(struct ll_readahead_state *ras, pgoff_t index)
{
        ras->ras_consecutive_requests = 0;
        ras->ras_consecutive_bytes = 0;
        ras->ras_window_pages = 0;
        ras_set_start(ras, index);
        ras->ras_next_readahead_idx = max(ras->ras_window_start_idx, index + 1);

        RAS_CDEBUG(ras);
}

/* called with the ras_lock held or from places where it doesn't matter */
static void ras_stride_reset(struct ll_readahead_state *ras)
{
        ras->ras_consecutive_stride_requests = 0;
        ras->ras_stride_length = 0;
        ras->ras_stride_bytes = 0;
        RAS_CDEBUG(ras);
}

void ll_readahead_init(struct inode *inode, struct ll_readahead_state *ras)
{
        spin_lock_init(&ras->ras_lock);
        ras->ras_rpc_pages = PTLRPC_MAX_BRW_PAGES;
        ras_reset(ras, 0);
        ras->ras_last_read_end_bytes = 0;
        ras->ras_requests = 0;
        ras->ras_range_min_start_idx = 0;
        ras->ras_range_max_end_idx = 0;
        ras->ras_range_requests = 0;
        ras->ras_last_range_pages = 0;
}

/*
 * Check whether the read request is in the stride window.
 * If it is in the stride window, return true, otherwise return false.
 */
static bool read_in_stride_window(struct ll_readahead_state *ras,
                                  loff_t pos, loff_t bytes)
{
        loff_t stride_gap;

        if (ras->ras_stride_length == 0 || ras->ras_stride_bytes == 0 ||
            ras->ras_stride_bytes == ras->ras_stride_length)
                return false;

        stride_gap = pos - ras->ras_last_read_end_bytes - 1;

        /* If it is contiguous read */
        if (stride_gap == 0)
                return ras->ras_consecutive_bytes + bytes <=
                        ras->ras_stride_bytes;

        /* Otherwise check the stride by itself */
        return (ras->ras_stride_length - ras->ras_stride_bytes) == stride_gap &&
                ras->ras_consecutive_bytes == ras->ras_stride_bytes &&
                bytes <= ras->ras_stride_bytes;
}

static void ras_init_stride_detector(struct ll_readahead_state *ras,
                                     loff_t pos, loff_t bytes)
{
        loff_t stride_gap = pos - ras->ras_last_read_end_bytes - 1;

        LASSERT(ras->ras_consecutive_stride_requests == 0);

        if (pos <= ras->ras_last_read_end_bytes) {
                /* Reset stride window for forward read */
                ras_stride_reset(ras);
                return;
        }

        ras->ras_stride_bytes = ras->ras_consecutive_bytes;
        ras->ras_stride_length = stride_gap + ras->ras_consecutive_bytes;
        ras->ras_consecutive_stride_requests++;
        ras->ras_stride_offset = pos;

        RAS_CDEBUG(ras);
}

static unsigned long
stride_page_count(struct ll_readahead_state *ras, loff_t len)
{
        loff_t bytes_count =
                stride_byte_count(ras->ras_stride_offset,
                                  ras->ras_stride_length, ras->ras_stride_bytes,
                                  ras->ras_window_start_idx << PAGE_SHIFT, len);

        return (bytes_count + PAGE_SIZE - 1) >> PAGE_SHIFT;
}

/* Stride Read-ahead window will be increased inc_len according to
 * stride I/O pattern */
static void ras_stride_increase_window(struct ll_readahead_state *ras,
                                       struct ll_ra_info *ra, loff_t inc_bytes)
{
        loff_t window_bytes, stride_bytes;
        u64 left_bytes;
        u64 step;
        loff_t end;

        /* temporarily store in page units to reduce LASSERT() cost below */
        end = ras->ras_window_start_idx + ras->ras_window_pages;

        LASSERT(ras->ras_stride_length > 0);
        LASSERTF(end >= (ras->ras_stride_offset >> PAGE_SHIFT),
                 "window_start_idx %lu, window_pages %lu stride_offset %llu\n",
                 ras->ras_window_start_idx, ras->ras_window_pages,
                 ras->ras_stride_offset);

        end <<= PAGE_SHIFT;
        if (end <= ras->ras_stride_offset)
                stride_bytes = 0;
        else
                stride_bytes = end - ras->ras_stride_offset;

        div64_u64_rem(stride_bytes, ras->ras_stride_length, &left_bytes);
        window_bytes = (ras->ras_window_pages << PAGE_SHIFT);
        if (left_bytes < ras->ras_stride_bytes) {
                if (ras->ras_stride_bytes - left_bytes >= inc_bytes) {
                        window_bytes += inc_bytes;
                        goto out;
                } else {
                        window_bytes += (ras->ras_stride_bytes - left_bytes);
                        inc_bytes -= (ras->ras_stride_bytes - left_bytes);
                }
        } else {
                window_bytes += (ras->ras_stride_length - left_bytes);
        }

        LASSERT(ras->ras_stride_bytes != 0);

        step = div64_u64_rem(inc_bytes, ras->ras_stride_bytes, &left_bytes);

        window_bytes += step * ras->ras_stride_length + left_bytes;
        LASSERT(window_bytes > 0);

out:
        if (stride_page_count(ras, window_bytes) <=
            ra->ra_max_pages_per_file || ras->ras_window_pages == 0)
                ras->ras_window_pages = (window_bytes >> PAGE_SHIFT);

        LASSERT(ras->ras_window_pages > 0);

        RAS_CDEBUG(ras);
}

static void ras_increase_window(struct inode *inode,
                                struct ll_readahead_state *ras,
                                struct ll_ra_info *ra)
{
        /* The stretch of ra-window should be aligned with max rpc_size
         * but current clio architecture does not support retrieve such
         * information from lower layer. FIXME later
         */
        if (stride_io_mode(ras)) {
                ras_stride_increase_window(ras, ra,
                                      (loff_t)ras->ras_rpc_pages << PAGE_SHIFT);
        } else {
                pgoff_t window_pages;

                window_pages = min(ras->ras_window_pages + ras->ras_rpc_pages,
                                   ra->ra_max_pages_per_file);
                if (window_pages < ras->ras_rpc_pages)
                        ras->ras_window_pages = window_pages;
                else
                        ras->ras_window_pages = ras_align(ras, window_pages);
        }
}

/**
 * Seek within 8 pages are considered as sequential read for now.
 */
static inline bool is_loose_seq_read(struct ll_readahead_state *ras, loff_t pos)
{
        return pos_in_window(pos, ras->ras_last_read_end_bytes,
                             8UL << PAGE_SHIFT, 8UL << PAGE_SHIFT);
}

static inline bool is_loose_mmap_read(struct ll_sb_info *sbi,
                                      struct ll_readahead_state *ras,
                                      unsigned long pos)
{
        unsigned long range_pages = sbi->ll_ra_info.ra_range_pages;

        return pos_in_window(pos, ras->ras_last_read_end_bytes,
                             range_pages << PAGE_SHIFT,
                             range_pages << PAGE_SHIFT);
}

/**
 * We have observed slow mmap read performances for some
 * applications. The problem is if access pattern is neither
 * sequential nor stride, but could be still adjacent in a
 * small range and then seek a random position.
 *
 * So the pattern could be something like this:
 *
 * [1M data] [hole] [0.5M data] [hole] [0.7M data] [1M data]
 *
 *
 * Every time an application reads mmap data, it may not only
 * read a single 4KB page, but aslo a cluster of nearby pages in
 * a range(e.g. 1MB) of the first page after a cache miss.
 *
 * The readahead engine is modified to track the range size of
 * a cluster of mmap reads, so that after a seek and/or cache miss,
 * the range size is used to efficiently prefetch multiple pages
 * in a single RPC rather than many small RPCs.
 */
static void ras_detect_cluster_range(struct ll_readahead_state *ras,
                                     struct ll_sb_info *sbi,
                                     unsigned long pos, unsigned long count)
{
        pgoff_t last_pages, pages;
        pgoff_t end_idx = (pos + count - 1) >> PAGE_SHIFT;

        last_pages = ras->ras_range_max_end_idx -
                        ras->ras_range_min_start_idx + 1;
        /* First time come here */
        if (!ras->ras_range_max_end_idx)
                goto out;

        /* Random or Stride read */
        if (!is_loose_mmap_read(sbi, ras, pos))
                goto out;

        ras->ras_range_requests++;
        if (ras->ras_range_max_end_idx < end_idx)
                ras->ras_range_max_end_idx = end_idx;

        if (ras->ras_range_min_start_idx > (pos >> PAGE_SHIFT))
                ras->ras_range_min_start_idx = pos >> PAGE_SHIFT;

        /* Out of range, consider it as random or stride */
        pages = ras->ras_range_max_end_idx -
                        ras->ras_range_min_start_idx + 1;
        if (pages <= sbi->ll_ra_info.ra_range_pages)
                return;
out:
        ras->ras_last_range_pages = last_pages;
        ras->ras_range_requests = 0;
        ras->ras_range_min_start_idx = pos >> PAGE_SHIFT;
        ras->ras_range_max_end_idx = end_idx;
}

static void ras_detect_read_pattern(struct ll_readahead_state *ras,
                                    struct ll_sb_info *sbi,
                                    loff_t pos, size_t bytes, bool mmap)
{
        bool stride_detect = false;
        pgoff_t index = pos >> PAGE_SHIFT;

        /*
         * Reset the read-ahead window in two cases. First when the app seeks
         * or reads to some other part of the file. Secondly if we get a
         * read-ahead miss that we think we've previously issued. This can
         * be a symptom of there being so many read-ahead pages that the VM
         * is reclaiming it before we get to it.
         */
        if (!is_loose_seq_read(ras, pos)) {
                /* Check whether it is in stride I/O mode */
                if (!read_in_stride_window(ras, pos, bytes)) {
                        if (ras->ras_consecutive_stride_requests == 0)
                                ras_init_stride_detector(ras, pos, bytes);
                        else
                                ras_stride_reset(ras);
                        ras->ras_consecutive_bytes = 0;
                        ras_reset(ras, index);
                } else {
                        ras->ras_consecutive_bytes = 0;
                        ras->ras_consecutive_requests = 0;
                        if (++ras->ras_consecutive_stride_requests > 1)
                                stride_detect = true;
                        RAS_CDEBUG(ras);
                }
                ll_ra_stats_inc_sbi(sbi, RA_STAT_DISTANT_READPAGE);
        } else if (stride_io_mode(ras)) {
                /*
                 * If this is contiguous read but in stride I/O mode
                 * currently, check whether stride step still is valid,
                 * if invalid, it will reset the stride ra window to
                 * be zero.
                 */
                if (!read_in_stride_window(ras, pos, bytes)) {
                        ras_stride_reset(ras);
                        ras->ras_window_pages = 0;
                        ras->ras_next_readahead_idx = index;
                }
        }

        ras->ras_consecutive_bytes += bytes;
        if (mmap) {
                pgoff_t idx = ras->ras_consecutive_bytes >> PAGE_SHIFT;
                unsigned long ra_range_pages =
                                max_t(unsigned long, RA_MIN_MMAP_RANGE_PAGES,
                                      sbi->ll_ra_info.ra_range_pages);

                if ((idx >= ra_range_pages &&
                     idx % ra_range_pages == 0) || stride_detect)
                        ras->ras_need_increase_window = true;
        } else if ((ras->ras_consecutive_requests > 1 || stride_detect)) {
                ras->ras_need_increase_window = true;
        }

        ras->ras_last_read_end_bytes = pos + bytes - 1;
}

void ll_ras_enter(struct file *f, loff_t pos, size_t bytes)
{
        struct ll_file_data *fd = f->private_data;
        struct ll_readahead_state *ras = &fd->fd_ras;
        struct inode *inode = file_inode(f);
        unsigned long index = pos >> PAGE_SHIFT;
        struct ll_sb_info *sbi = ll_i2sbi(inode);

        spin_lock(&ras->ras_lock);
        ras->ras_requests++;
        ras->ras_consecutive_requests++;
        ras->ras_need_increase_window = false;
        ras->ras_no_miss_check = false;
        /*
         * On the second access to a file smaller than the tunable
         * ra_max_read_ahead_whole_pages trigger RA on all pages in the
         * file up to ra_max_pages_per_file.  This is simply a best effort
         * and only occurs once per open file. Normal RA behavior is reverted
         * to for subsequent IO.
         */
        if (ras->ras_requests >= 2) {
                __u64 kms_pages;
                struct ll_ra_info *ra = &sbi->ll_ra_info;

                kms_pages = (i_size_read(inode) + PAGE_SIZE - 1) >>
                            PAGE_SHIFT;

                CDEBUG(D_READA, "kmsp %llu mwp %lu mp %lu\n", kms_pages,
                       ra->ra_max_read_ahead_whole_pages,
                       ra->ra_max_pages_per_file);

                if (kms_pages &&
                    kms_pages <= ra->ra_max_read_ahead_whole_pages) {
                        ras->ras_window_start_idx = 0;
                        ras->ras_next_readahead_idx = index + 1;
                        ras->ras_window_pages = min(ra->ra_max_pages_per_file,
                                            ra->ra_max_read_ahead_whole_pages);
                        ras->ras_no_miss_check = true;
                        GOTO(out_unlock, 0);
                }
        }
        ras_detect_read_pattern(ras, sbi, pos, bytes, false);
out_unlock:
        spin_unlock(&ras->ras_lock);
}

static bool index_in_stride_window(struct ll_readahead_state *ras,
                                   pgoff_t index)
{
        loff_t pos = (loff_t)index << PAGE_SHIFT;

        if (ras->ras_stride_length == 0 || ras->ras_stride_bytes == 0 ||
            ras->ras_stride_bytes == ras->ras_stride_length)
                return false;

        if (pos >= ras->ras_stride_offset) {
                u64 offset;

                div64_u64_rem(pos - ras->ras_stride_offset,
                              ras->ras_stride_length, &offset);
                if (offset < ras->ras_stride_bytes ||
                    ras->ras_stride_length - offset < PAGE_SIZE)
                        return true;
        } else if (ras->ras_stride_offset - pos < PAGE_SIZE) {
                return true;
        }

        return false;
}

/*
 * ll_ras_enter() is used to detect read pattern according to pos and count.
 *
 * ras_update() is used to detect cache miss and
 * reset window or increase window accordingly
 */
static void ras_update(struct ll_sb_info *sbi, struct inode *inode,
                       struct ll_readahead_state *ras, pgoff_t index,
                       enum ras_update_flags flags, struct cl_io *io)
{
        struct ll_ra_info *ra = &sbi->ll_ra_info;
        bool hit = flags & LL_RAS_HIT;

        ENTRY;
        spin_lock(&ras->ras_lock);

        if (!hit)
                CDEBUG(D_READA|D_IOTRACE, DFID " pages at %lu miss.\n",
                       PFID(ll_inode2fid(inode)), index);
        ll_ra_stats_inc_sbi(sbi, hit ? RA_STAT_HIT : RA_STAT_MISS);

        /*
         * The readahead window has been expanded to cover whole
         * file size, we don't care whether ra miss happen or not.
         * Because we will read whole file to page cache even if
         * some pages missed.
         */
        if (ras->ras_no_miss_check)
                GOTO(out_unlock, 0);

        if (io && io->ci_rand_read)
                GOTO(out_unlock, 0);

        if (io && io->ci_seq_read) {
                if (!hit) {
                        /* to avoid many small read RPC here */
                        ras->ras_window_pages = sbi->ll_ra_info.ra_range_pages;
                        ll_ra_stats_inc_sbi(sbi, RA_STAT_MMAP_RANGE_READ);
                }
                goto skip;
        }

        if (flags & LL_RAS_MMAP) {
                unsigned long ra_pages;

                ras_detect_cluster_range(ras, sbi, index << PAGE_SHIFT,
                                         PAGE_SIZE);
                ras_detect_read_pattern(ras, sbi, (loff_t)index << PAGE_SHIFT,
                                        PAGE_SIZE, true);

                /* we did not detect anything but we could prefetch */
                if (!ras->ras_need_increase_window &&
                    ras->ras_window_pages <= sbi->ll_ra_info.ra_range_pages &&
                    ras->ras_range_requests >= 2) {
                        if (!hit) {
                                ra_pages = max_t(unsigned long,
                                        RA_MIN_MMAP_RANGE_PAGES,
                                        ras->ras_last_range_pages);
                                if (index < ra_pages / 2)
                                        index = 0;
                                else
                                        index -= ra_pages / 2;
                                ras->ras_window_pages = ra_pages;
                                ll_ra_stats_inc_sbi(sbi,
                                        RA_STAT_MMAP_RANGE_READ);
                        } else {
                                ras->ras_window_pages = 0;
                        }
                        goto skip;
                }
        }

        if (!hit && ras->ras_window_pages &&
            index < ras->ras_next_readahead_idx &&
            pos_in_window(index, ras->ras_window_start_idx, 0,
                          ras->ras_window_pages)) {
                ll_ra_stats_inc_sbi(sbi, RA_STAT_MISS_IN_WINDOW);
                ras->ras_need_increase_window = false;

                if (index_in_stride_window(ras, index) &&
                    stride_io_mode(ras)) {
                        /*
                         * if (index != ras->ras_last_readpage + 1)
                         *      ras->ras_consecutive_pages = 0;
                         */
                        ras_reset(ras, index);

                        /*
                         * If stride-RA hit cache miss, the stride
                         * detector will not be reset to avoid the
                         * overhead of redetecting read-ahead mode,
                         * but on the condition that the stride window
                         * is still intersect with normal sequential
                         * read-ahead window.
                         */
                        if (ras->ras_window_start_idx < ras->ras_stride_offset)
                                ras_stride_reset(ras);
                        RAS_CDEBUG(ras);
                } else {
                        /*
                         * Reset both stride window and normal RA
                         * window.
                         */
                        ras_reset(ras, index);
                        /* ras->ras_consecutive_pages++; */
                        ras->ras_consecutive_bytes = 0;
                        ras_stride_reset(ras);
                        GOTO(out_unlock, 0);
                }
        }

skip:
        ras_set_start(ras, index);

        if (stride_io_mode(ras)) {
                /* Since stride readahead is sentivite to the offset
                 * of read-ahead, so we use original offset here,
                 * instead of ras_window_start_idx, which is RPC aligned.
                 */
                ras->ras_next_readahead_idx = max(index + 1,
                                                  ras->ras_next_readahead_idx);
                ras->ras_window_start_idx =
                                max_t(pgoff_t, ras->ras_window_start_idx,
                                      ras->ras_stride_offset >> PAGE_SHIFT);
        } else {
                if (ras->ras_next_readahead_idx < ras->ras_window_start_idx)
                        ras->ras_next_readahead_idx = ras->ras_window_start_idx;
                if (!hit)
                        ras->ras_next_readahead_idx = index + 1;
        }

        if (ras->ras_need_increase_window) {
                ras_increase_window(inode, ras, ra);
                ras->ras_need_increase_window = false;
        }

        EXIT;
out_unlock:
        spin_unlock(&ras->ras_lock);
}

int ll_writepage(struct page *vmpage, struct writeback_control *wbc)
{
        struct inode           *inode = vmpage->mapping->host;
        struct ll_inode_info   *lli   = ll_i2info(inode);
        struct lu_env          *env;
        struct cl_io           *io;
        struct cl_page         *page;
        struct cl_object       *clob;
        bool redirtied = false;
        bool unlocked = false;
        int result;
        __u16 refcheck;
        ENTRY;

        LASSERT(PageLocked(vmpage));
        LASSERT(!PageWriteback(vmpage));

        LASSERT(ll_i2dtexp(inode) != NULL);

        env = cl_env_get(&refcheck);
        if (IS_ERR(env))
                GOTO(out, result = PTR_ERR(env));

        clob  = ll_i2info(inode)->lli_clob;
        LASSERT(clob != NULL);

        io = vvp_env_thread_io(env);
        io->ci_obj = clob;
        io->ci_ignore_layout = 1;
        result = cl_io_init(env, io, CIT_MISC, clob);
        if (result == 0) {
                page = cl_page_find(env, clob, vmpage->index,
                                    vmpage, CPT_CACHEABLE);
                if (!IS_ERR(page)) {
                        lu_ref_add(&page->cp_reference, "writepage",
                                   current);
                        cl_page_assume(env, io, page);
                        result = cl_page_flush(env, io, page);
                        if (result != 0) {
                                /*
                                 * Re-dirty page on error so it retries write,
                                 * but not in case when IO has actually
                                 * occurred and completed with an error.
                                 */
                                if (!PageError(vmpage)) {
                                        redirty_page_for_writepage(wbc, vmpage);
                                        result = 0;
                                        redirtied = true;
                                }
                        }
                        cl_page_disown(env, io, page);
                        unlocked = true;
                        lu_ref_del(&page->cp_reference,
                                   "writepage", current);
                        cl_page_put(env, page);
                } else {
                        result = PTR_ERR(page);
                }
        }
        cl_io_fini(env, io);

        if (redirtied && wbc->sync_mode == WB_SYNC_ALL) {
                loff_t offset = vmpage->index << PAGE_SHIFT;

                /* Flush page failed because the extent is being written out.
                 * Wait for the write of extent to be finished to avoid
                 * breaking kernel which assumes ->writepage should mark
                 * PageWriteback or clean the page. */
                result = cl_sync_file_range(inode, offset,
                                            offset + PAGE_SIZE - 1,
                                            CL_FSYNC_LOCAL, 1);
                if (result > 0) {
                        /* actually we may have written more than one page.
                         * decreasing this page because the caller will count
                         * it. */
                        wbc->nr_to_write -= result - 1;
                        result = 0;
                }
        }

        cl_env_put(env, &refcheck);
        GOTO(out, result);

out:
        if (result < 0) {
                if (!lli->lli_async_rc)
                        lli->lli_async_rc = result;
                SetPageError(vmpage);
                if (!unlocked)
                        unlock_page(vmpage);
        }
        return result;
}

int ll_writepages(struct address_space *mapping, struct writeback_control *wbc)
{
        struct inode *inode = mapping->host;
        loff_t start;
        loff_t end;
        enum cl_fsync_mode mode;
        int range_whole = 0;
        int result;

        ENTRY;

        if (wbc->range_cyclic) {
                start = (loff_t)mapping->writeback_index << PAGE_SHIFT;
                end = OBD_OBJECT_EOF;
        } else {
                start = wbc->range_start;
                end = wbc->range_end;
                if (end == LLONG_MAX) {
                        end = OBD_OBJECT_EOF;
                        range_whole = start == 0;
                }
        }

        mode = CL_FSYNC_NONE;
        if (wbc->sync_mode == WB_SYNC_ALL)
                mode = CL_FSYNC_LOCAL;

        if (wbc->sync_mode == WB_SYNC_NONE) {
#ifdef SB_I_CGROUPWB
                struct bdi_writeback *wb;

                /*
                 * As it may break full stripe writes on the inode,
                 * disable periodic kupdate writeback (@wbc->for_kupdate)?
                 */

                /*
                 * The system is under memory pressure and it is now reclaiming
                 * cache pages.
                 */
                wb = inode_to_wb(inode);
                if (wbc->for_background ||
                    (wb->start_all_reason == WB_REASON_VMSCAN &&
                     test_bit(WB_start_all, &wb->state)))
                        mode = CL_FSYNC_RECLAIM;
#else
                /*
                 * We have no idea about writeback reason for memory reclaim
                 * WB_REASON_TRY_TO_FREE_PAGES in the old kernel such as rhel7
                 * (WB_REASON_VMSCAN in the newer kernel) ...
                 * Here set mode with CL_FSYNC_RECLAIM forcely on the old
                 * kernel.
                 */
                if (!wbc->for_kupdate)
                        mode = CL_FSYNC_RECLAIM;
#endif
        }

        if (ll_i2info(inode)->lli_clob == NULL)
                RETURN(0);

        /* for directio, it would call writepages() to evict cached pages
         * inside the IO context of write, which will cause deadlock at
         * layout_conf since it waits for active IOs to complete. */
        result = cl_sync_file_range(inode, start, end, mode, 1);
        if (result > 0) {
                wbc->nr_to_write -= result;
                result = 0;
         }

        if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0)) {
                if (end == OBD_OBJECT_EOF)
                        mapping->writeback_index = 0;
                else
                        mapping->writeback_index = (end >> PAGE_SHIFT) + 1;
        }
        RETURN(result);
}

struct ll_cl_context *ll_cl_find(struct inode *inode)
{
        struct ll_inode_info *lli = ll_i2info(inode);
        struct ll_cl_context *lcc;
        struct ll_cl_context *found = NULL;

        read_lock(&lli->lli_lock);
        list_for_each_entry(lcc, &lli->lli_lccs, lcc_list) {
                if (lcc->lcc_cookie == current) {
                        found = lcc;
                        break;
                }
        }
        read_unlock(&lli->lli_lock);

        return found;
}

void ll_cl_add(struct inode *inode, const struct lu_env *env, struct cl_io *io,
               enum lcc_type type)
{
        struct ll_inode_info *lli = ll_i2info(inode);
        struct ll_cl_context *lcc = &ll_env_info(env)->lti_io_ctx;

        memset(lcc, 0, sizeof(*lcc));
        INIT_LIST_HEAD(&lcc->lcc_list);
        lcc->lcc_cookie = current;
        lcc->lcc_env = env;
        lcc->lcc_io = io;
        lcc->lcc_type = type;

        write_lock(&lli->lli_lock);
        list_add(&lcc->lcc_list, &lli->lli_lccs);
        write_unlock(&lli->lli_lock);
}

void ll_cl_remove(struct inode *inode, const struct lu_env *env)
{
        struct ll_inode_info *lli = ll_i2info(inode);
        struct ll_cl_context *lcc = &ll_env_info(env)->lti_io_ctx;

        write_lock(&lli->lli_lock);
        list_del_init(&lcc->lcc_list);
        write_unlock(&lli->lli_lock);
}

int ll_io_read_page(const struct lu_env *env, struct cl_io *io,
                           struct cl_page *page, struct file *file)
{
        struct inode              *inode  = vvp_object_inode(page->cp_obj);
        struct ll_sb_info         *sbi    = ll_i2sbi(inode);
        struct ll_file_data       *fd     = NULL;
        struct ll_readahead_state *ras    = NULL;
        struct cl_2queue          *queue  = &io->ci_queue;
        struct cl_sync_io         *anchor = NULL;
        int                        rc = 0, rc2 = 0;
        bool                       uptodate;
        struct vvp_io *vio = vvp_env_io(env);
        bool mmap = !vio->vui_ra_valid;
        pgoff_t ra_start_index = 0;
        pgoff_t io_start_index;
        pgoff_t io_end_index;
        bool unlockpage = true;
        ENTRY;

        if (file) {
                fd = file->private_data;
                ras = &fd->fd_ras;
        }

        /* PagePrivate2 is set in ll_io_zero_page() to tell us the vmpage
         * must not be unlocked after processing.
         */
        if (page->cp_vmpage && PagePrivate2(page->cp_vmpage))
                unlockpage = false;

        uptodate = page->cp_defer_uptodate;

        if (ll_readahead_enabled(sbi) && !page->cp_ra_updated && ras) {
                enum ras_update_flags flags = 0;

                if (uptodate)
                        flags |= LL_RAS_HIT;
                if (mmap)
                        flags |= LL_RAS_MMAP;
                ras_update(sbi, inode, ras, cl_page_index(page), flags, io);
        }

        cl_2queue_init(queue);
        if (uptodate) {
                page->cp_ra_used = 1;
                SetPageUptodate(page->cp_vmpage);
                cl_page_disown(env, io, page);
        } else {
                anchor = &vvp_env_info(env)->vti_anchor;
                cl_sync_io_init(anchor, 1);
                page->cp_sync_io = anchor;

                cl_page_list_add(&queue->c2_qin, page, true);
        }

        /* mmap does not set the ci_rw fields */
        if (!mmap) {
                io_start_index = io->u.ci_rw.crw_pos >> PAGE_SHIFT;
                io_end_index = (io->u.ci_rw.crw_pos +
                                io->u.ci_rw.crw_bytes - 1) >> PAGE_SHIFT;
        } else {
                io_start_index = cl_page_index(page);
                io_end_index = cl_page_index(page);
        }

        if (ll_readahead_enabled(sbi) && ras && !io->ci_rand_read) {
                pgoff_t skip_index = 0;

                if (ras->ras_next_readahead_idx < cl_page_index(page))
                        skip_index = cl_page_index(page);
                rc2 = ll_readahead(env, io, &queue->c2_qin, ras,
                                   uptodate, file, skip_index,
                                   &ra_start_index);
                /* to keep iotrace clean, we only print here if we actually
                 * read pages
                 */
                CDEBUG(D_READA | (rc2 ? D_IOTRACE : 0),
                       DFID " %d pages read ahead at %lu, triggered by user read at %lu, stride offset %lld, stride length %lld, stride bytes %lld\n",
                       PFID(ll_inode2fid(inode)), rc2, ra_start_index,
                       cl_page_index(page), ras->ras_stride_offset,
                       ras->ras_stride_length, ras->ras_stride_bytes);

        } else if (cl_page_index(page) == io_start_index &&
                   io_end_index - io_start_index > 0) {
                rc2 = ll_readpages(env, io, &queue->c2_qin, io_start_index + 1,
                                   io_end_index);
                CDEBUG(D_READA, DFID " %d pages read at %lu\n",
                       PFID(ll_inode2fid(inode)), rc2, cl_page_index(page));
        }

        if (queue->c2_qin.pl_nr > 0) {
                int count = queue->c2_qin.pl_nr;
                rc = cl_io_submit_rw(env, io, CRT_READ, queue);
                if (rc == 0)
                        task_io_account_read(PAGE_SIZE * count);
        }


        if (anchor != NULL && !cl_page_is_owned(page, io)) { /* have sent */
                rc = cl_sync_io_wait(env, anchor, 0);

                cl_page_assume(env, io, page);
                cl_page_list_del(env, &queue->c2_qout, page);

                if (!PageUptodate(cl_page_vmpage(page))) {
                        /* Failed to read a mirror, discard this page so that
                         * new page can be created with new mirror.
                         *
                         * TODO: this is not needed after page reinit
                         * route is implemented */
                        cl_page_discard(env, io, page);
                }
                if (unlockpage)
                        cl_page_disown(env, io, page);
        }

        /* TODO: discard all pages until page reinit route is implemented */
        cl_page_list_discard(env, io, &queue->c2_qin);

        /* Unlock unsent read pages in case of error. */
        cl_page_list_disown(env, &queue->c2_qin);

        cl_2queue_fini(env, queue);

        RETURN(rc);
}

/*
 * Possible return value:
 * 0 no async readahead triggered and fast read could not be used.
 * 1 no async readahead, but fast read could be used.
 * 2 async readahead triggered and fast read could be used too.
 * < 0 on error.
 */
static int kickoff_async_readahead(struct file *file, unsigned long pages)
{
        struct ll_readahead_work *lrw;
        struct inode *inode = file_inode(file);
        struct ll_sb_info *sbi = ll_i2sbi(inode);
        struct ll_file_data *fd = file->private_data;
        struct ll_readahead_state *ras = &fd->fd_ras;
        struct ll_ra_info *ra = &sbi->ll_ra_info;
        unsigned long throttle;
        pgoff_t start_idx = ras_align(ras, ras->ras_next_readahead_idx);
        pgoff_t end_idx = start_idx + pages - 1;

        /**
         * In case we have a limited max_cached_mb, readahead
         * should be stopped if it have run out of all LRU slots.
         */
        if (atomic_read(&ra->ra_cur_pages) >= sbi->ll_cache->ccc_lru_max) {
                ll_ra_stats_inc(inode, RA_STAT_MAX_IN_FLIGHT);
                return 0;
        }

        throttle = min(ra->ra_async_pages_per_file_threshold,
                       ra->ra_max_pages_per_file);
        /*
         * If this is strided i/o or the window is smaller than the
         * throttle limit, we do not do async readahead. Otherwise,
         * we do async readahead, allowing the user thread to do fast i/o.
         */
        if (stride_io_mode(ras) || !throttle ||
            ras->ras_window_pages < throttle ||
            atomic_read(&ra->ra_async_inflight) > ra->ra_async_max_active)
                return 0;

        if ((atomic_read(&ra->ra_cur_pages) + pages) > ra->ra_max_pages)
                return 0;

        if (ras->ras_async_last_readpage_idx == start_idx)
                return 1;

        /* ll_readahead_work_free() free it */
        OBD_ALLOC_PTR(lrw);
        if (lrw) {
                atomic_inc(&sbi->ll_ra_info.ra_async_inflight);
                lrw->lrw_file = get_file(file);
                lrw->lrw_start_idx = start_idx;
                lrw->lrw_end_idx = end_idx;
                lrw->lrw_user_pid = current->pid;
                spin_lock(&ras->ras_lock);
                ras->ras_next_readahead_idx = end_idx + 1;
                ras->ras_async_last_readpage_idx = start_idx;
                spin_unlock(&ras->ras_lock);
                memcpy(lrw->lrw_jobid, ll_i2info(inode)->lli_jobid,
                       sizeof(lrw->lrw_jobid));
                ll_readahead_work_add(inode, lrw);
        } else {
                return -ENOMEM;
        }

        return 2;
}

/*
 * Check if we can issue a readahead RPC, if that is
 * the case, we can't do fast IO because we will need
 * a cl_io to issue the RPC.
 */
static bool ll_use_fast_io(struct file *file,
                           struct ll_readahead_state *ras, pgoff_t index)
{
        unsigned long fast_read_pages =
                max(RA_REMAIN_WINDOW_MIN, ras->ras_rpc_pages);
        loff_t skip_pages;
        loff_t stride_bytes = ras->ras_stride_bytes;

        RAS_CDEBUG(ras);

        if (stride_io_mode(ras) && stride_bytes) {
                skip_pages = (ras->ras_stride_length +
                        ras->ras_stride_bytes - 1) / stride_bytes;
                skip_pages *= fast_read_pages;
        } else {
                skip_pages = fast_read_pages;
        }

        if (ras->ras_window_start_idx + ras->ras_window_pages <
            ras->ras_next_readahead_idx + skip_pages ||
            kickoff_async_readahead(file, fast_read_pages) > 0)
                return true;

        return false;
}

int ll_readpage(struct file *file, struct page *vmpage)
{
        struct inode *inode = file_inode(file);
        struct cl_object *clob = ll_i2info(inode)->lli_clob;
        struct ll_sb_info *sbi = ll_i2sbi(inode);
        const struct lu_env *env = NULL;
        struct cl_read_ahead ra = { 0 };
        struct ll_cl_context *lcc;
        struct cl_io *io = NULL;
        struct cl_page *page;
        struct vvp_io *vio;
        int result;
        int flags;

        ENTRY;

        if (CFS_FAIL_PRECHECK(OBD_FAIL_LLITE_READPAGE_PAUSE)) {
                unlock_page(vmpage);
                CFS_FAIL_TIMEOUT(OBD_FAIL_LLITE_READPAGE_PAUSE, cfs_fail_val);
                lock_page(vmpage);
        }

        /*
         * The @vmpage got truncated.
         * This is a kernel bug introduced since kernel 5.12:
         * comment: cbd59c48ae2bcadc4a7599c29cf32fd3f9b78251
         * ("mm/filemap: use head pages in generic_file_buffered_read")
         *
         * The page end offset calculation in filemap_get_read_batch() was off
         * by one.  When a read is submitted with end offset 1048575, then it
         * calculates the end page for read of 256 where it should be 255. This
         * results in the readpage() for the page with index 256 is over stripe
         * boundary and may not covered by a DLM extent lock.
         *
         * This happens in a corner race case: filemap_get_read_batch() adds
         * the page with index 256 for read which is not in the current read
         * I/O context, and this page is being invalidated and will be removed
         * from page cache due to the lock protected it being revoken. This
         * results in this page in the read path not covered by any DLM lock.
         *
         * The solution is simple. Check whether the page was truncated in
         * ->readpage(). If so, just return AOP_TRUNCATED_PAGE to the upper
         * caller. Then the kernel will retry to batch pages, and it will not
         * add the truncated page into batches as it was removed from page
         * cache of the file.
         */
        if (vmpage->mapping != inode->i_mapping) {
                unlock_page(vmpage);
                RETURN(AOP_TRUNCATED_PAGE);
        }

        lcc = ll_cl_find(inode);
        if (lcc != NULL) {
                env = lcc->lcc_env;
                io  = lcc->lcc_io;
        }

        if (io == NULL) { /* fast read */
                struct inode *inode = file_inode(file);
                struct ll_file_data *fd = file->private_data;
                struct ll_readahead_state *ras = &fd->fd_ras;
                struct lu_env  *local_env = NULL;

                CDEBUG(D_VFSTRACE, "fast read pgno: %ld\n", vmpage->index);

                result = -ENODATA;

                /* TODO: need to verify the layout version to make sure
                 * the page is not invalid due to layout change. */
                page = cl_vmpage_page(vmpage, clob);
                if (page == NULL) {
                        unlock_page(vmpage);
                        ll_ra_stats_inc_sbi(sbi, RA_STAT_FAILED_FAST_READ);
                        RETURN(result);
                }

                if (page->cp_defer_uptodate) {
                        enum ras_update_flags flags = LL_RAS_HIT;

                        if (lcc && lcc->lcc_type == LCC_MMAP)
                                flags |= LL_RAS_MMAP;

                        /* For fast read, it updates read ahead state only
                         * if the page is hit in cache because non cache page
                         * case will be handled by slow read later. */
                        ras_update(sbi, inode, ras, cl_page_index(page), flags, io);
                        /* avoid duplicate ras_update() call */
                        page->cp_ra_updated = 1;

                        if (ll_use_fast_io(file, ras, cl_page_index(page)))
                                result = 0;
                }

                if (!env) {
                        local_env = cl_env_percpu_get();
                        env = local_env;
                }

                /* export the page and skip io stack */
                if (result == 0) {
                        page->cp_ra_used = 1;
                        SetPageUptodate(vmpage);
                } else {
                        ll_ra_stats_inc_sbi(sbi, RA_STAT_FAILED_FAST_READ);
                }

                /* release page refcount before unlocking the page to ensure
                 * the object won't be destroyed in the calling path of
                 * cl_page_put(). Please see comment in ll_releasepage(). */
                cl_page_put(env, page);
                unlock_page(vmpage);
                if (local_env)
                        cl_env_percpu_put(local_env);

                RETURN(result);
        }

        if (lcc && lcc->lcc_type != LCC_MMAP) {
                /*
                 * This handles a kernel bug introduced in kernel 5.12:
                 * comment: cbd59c48ae2bcadc4a7599c29cf32fd3f9b78251
                 * ("mm/filemap: use head pages in generic_file_buffered_read")
                 *
                 * See above in this function for a full description of the
                 * bug.  Briefly, the kernel will try to read 1 more page than
                 * was actually requested *if that page is already in cache*.
                 *
                 * Because this page is beyond the boundary of the requested
                 * read, Lustre does not lock it as part of the read.  This
                 * means we must check if there is a valid dlmlock on this
                 * this page and reference it before we attempt to read in the
                 * page.  If there is not a valid dlmlock, then we are racing
                 * with dlmlock cancellation and the page is being removed
                 * from the cache.
                 *
                 * That means we should return AOP_TRUNCATED_PAGE, which will
                 * cause the kernel to retry the read, which should allow the
                 * page to be removed from cache as the lock is cancelled.
                 *
                 * This should never occur except in kernels with the bug
                 * mentioned above.
                 */
                if (vmpage->index >= lcc->lcc_end_index) {
                        CDEBUG(D_VFSTRACE,
                               "pgno:%ld, beyond read end_index:%ld\n",
                               vmpage->index, lcc->lcc_end_index);

                        result = cl_io_read_ahead(env, io, vmpage->index, &ra);
                        if (result < 0 || vmpage->index > ra.cra_end_idx) {
                                cl_read_ahead_release(env, &ra);
                                unlock_page(vmpage);
                                RETURN(AOP_TRUNCATED_PAGE);
                        }
                }
        }

        vio = vvp_env_io(env);
        /**
         * Direct read can fall back to buffered read, but DIO is done
         * with lockless i/o, and buffered requires LDLM locking, so in
         * this case we must restart without lockless.
         */
        flags = iocb_ki_flags_get(file, vio->vui_iocb);
        if (iocb_ki_flags_check(flags, DIRECT) &&
            lcc && lcc->lcc_type == LCC_RW &&
            !io->ci_dio_lock) {
                unlock_page(vmpage);
                io->ci_dio_lock = 1;
                io->ci_need_restart = 1;
                GOTO(out, result = -ENOLCK);
        }

        LASSERT(io->ci_state == CIS_IO_GOING);
        page = cl_page_find(env, clob, vmpage->index, vmpage, CPT_CACHEABLE);
        if (!IS_ERR(page)) {
                LASSERT(page->cp_type == CPT_CACHEABLE);
                if (likely(!PageUptodate(vmpage))) {
                        cl_page_assume(env, io, page);

                        result = ll_io_read_page(env, io, page, file);
                } else {
                        /* Page from a non-object file. */
                        unlock_page(vmpage);
                        result = 0;
                }
                cl_page_put(env, page);
        } else {
                unlock_page(vmpage);
                result = PTR_ERR(page);
        }

out:
        if (ra.cra_release != NULL)
                cl_read_ahead_release(env, &ra);

        /* this delay gives time for the actual read of the page to finish and
         * unlock the page in vvp_page_completion_read before we return to our
         * caller and the caller tries to use the page, allowing us to test
         * races with the page being unlocked after readpage() but before it's
         * used by the caller
         */
        CFS_FAIL_TIMEOUT(OBD_FAIL_LLITE_READPAGE_PAUSE2, cfs_fail_val);

        RETURN(result);
}

#ifdef HAVE_AOPS_READ_FOLIO
int ll_read_folio(struct file *file, struct folio *folio)
{
        return ll_readpage(file, folio_page(folio, 0));
}
#endif