/*
 * 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, 2015, Intel Corporation.
 */
/*
 * This file is part of Lustre, http://www.lustre.org/
 * Lustre is a trademark of Sun Microsystems, Inc.
 *
 * 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 <linux/uaccess.h>

#include <linux/fs.h>
#include <linux/pagemap.h>
/* current_is_kswapd() */
#include <linux/swap.h>
#include <linux/bvec.h>

#define DEBUG_SUBSYSTEM S_LLITE

#include "../include/obd_cksum.h"
#include "llite_internal.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 min)
{
        struct ll_ra_info *ra = &sbi->ll_ra_info;
        long ret;

        /* 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)) {
                ret = 0;
                goto out;
        }

        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 < min) {
                /* override ra limit for maximum performance */
                atomic_add(min - ret, &ra->ra_cur_pages);
                ret = min;
        }
        return ret;
}

void ll_ra_count_put(struct ll_sb_info *sbi, unsigned long len)
{
        struct ll_ra_info *ra = &sbi->ll_ra_info;

        atomic_sub(len, &ra->ra_cur_pages);
}

static void ll_ra_stats_inc_sbi(struct ll_sb_info *sbi, enum ra_stat which)
{
        LASSERTF(which >= 0 && which < _NR_RA_STAT, "which: %u\n", which);
        lprocfs_counter_incr(sbi->ll_ra_stats, which);
}

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);
}

#define RAS_CDEBUG(ras) \
        CDEBUG(D_READA,                                               \
               "lrp %lu cr %lu cp %lu ws %lu wl %lu nra %lu rpc %lu "        \
               "r %lu ri %lu csr %lu sf %lu sp %lu sl %lu\n",                \
               ras->ras_last_readpage, ras->ras_consecutive_requests,   \
               ras->ras_consecutive_pages, ras->ras_window_start,           \
               ras->ras_window_len, ras->ras_next_readahead,             \
               ras->ras_rpc_size,                                            \
               ras->ras_requests, ras->ras_request_index,                   \
               ras->ras_consecutive_stride_requests, ras->ras_stride_offset, \
               ras->ras_stride_pages, ras->ras_stride_length)

static int index_in_window(unsigned long index, unsigned long point,
                           unsigned long before, unsigned long after)
{
        unsigned long start = point - before, end = point + after;

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

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

void ll_ras_enter(struct file *f)
{
        struct ll_file_data *fd = LUSTRE_FPRIVATE(f);
        struct ll_readahead_state *ras = &fd->fd_ras;

        spin_lock(&ras->ras_lock);
        ras->ras_requests++;
        ras->ras_request_index = 0;
        ras->ras_consecutive_requests++;
        spin_unlock(&ras->ras_lock);
}

/**
 * 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 ra_stat which = _NR_RA_STAT; /* keep gcc happy */
        struct cl_object *clob = io->ci_obj;
        struct inode *inode = vvp_object_inode(clob);
        const char *msg = NULL;
        struct cl_page *page;
        struct vvp_page *vpg;
        struct page *vmpage;
        int rc = 0;

        vmpage = grab_cache_page_nowait(inode->i_mapping, index);
        if (!vmpage) {
                which = RA_STAT_FAILED_GRAB_PAGE;
                msg = "g_c_p_n failed";
                rc = -EBUSY;
                goto out;
        }

        /* 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";
                rc = -EBUSY;
                goto out;
        }

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

        lu_ref_add(&page->cp_reference, "ra", current);
        cl_page_assume(env, io, page);
        vpg = cl2vvp_page(cl_object_page_slice(clob, page));
        if (!vpg->vpg_defer_uptodate && !PageUptodate(vmpage)) {
                vpg->vpg_defer_uptodate = 1;
                vpg->vpg_ra_used = 0;
                cl_page_list_add(queue, page);
        } else {
                /* skip completed pages */
                cl_page_unassume(env, io, page);
                /* This page is already uptodate, returning a positive number
                 * to tell the callers about this
                 */
                rc = 1;
        }

        lu_ref_del(&page->cp_reference, "ra", current);
        cl_page_put(env, page);
out:
        if (vmpage) {
                if (rc)
                        unlock_page(vmpage);
                put_page(vmpage);
        }
        if (msg) {
                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 %lu rl %lu rp %lu\n",       \
        ria->ria_start, ria->ria_end, ria->ria_stoff, ria->ria_length,\
        ria->ria_pages)

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

/* The function calculates how much pages will be read in
 * [off, off + length], in such stride IO area,
 * stride_offset = st_off, stride_length = st_len,
 * stride_pages = st_pgs
 *
 *   |------------------|*****|------------------|*****|------------|*****|....
 * st_off
 *   |--- st_pgs     ---|
 *   |-----     st_len   -----|
 *
 *            How many pages it should read in such pattern
 *            |-------------------------------------------------------------|
 *            off
 *            |<------            length                      ------->|
 *
 *        =   |<----->|  +  |-------------------------------------| +   |---|
 *           start_left          st_pgs * i                 end_left
 */
static unsigned long
stride_pg_count(pgoff_t st_off, unsigned long st_len, unsigned long st_pgs,
                unsigned long off, unsigned long length)
{
        __u64 start = off > st_off ? off - st_off : 0;
        __u64 end = off + length > st_off ? off + length - st_off : 0;
        unsigned long start_left = 0;
        unsigned long end_left = 0;
        unsigned long pg_count;

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

        start_left = do_div(start, st_len);
        if (start_left < st_pgs)
                start_left = st_pgs - start_left;
        else
                start_left = 0;

        end_left = do_div(end, st_len);
        if (end_left > st_pgs)
                end_left = st_pgs;

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

        if (start == end)
                pg_count = end_left - (st_pgs - start_left);
        else
                pg_count = start_left + st_pgs * (end - start - 1) + end_left;

        CDEBUG(D_READA, "st_off %lu, st_len %lu st_pgs %lu off %lu length %lu pgcount %lu\n",
               st_off, st_len, st_pgs, off, length, pg_count);

        return pg_count;
}

static int ria_page_count(struct ra_io_arg *ria)
{
        __u64 length = ria->ria_end >= ria->ria_start ?
                       ria->ria_end - ria->ria_start + 1 : 0;

        return stride_pg_count(ria->ria_stoff, ria->ria_length,
                               ria->ria_pages, ria->ria_start,
                               length);
}

static unsigned long ras_align(struct ll_readahead_state *ras,
                               unsigned long index,
                               unsigned long *remainder)
{
        unsigned long rem = index % ras->ras_rpc_size;

        if (remainder)
                *remainder = rem;
        return index - rem;
}

/*Check whether the index is in the defined ra-window */
static int ras_inside_ra_window(unsigned long idx, struct ra_io_arg *ria)
{
        /* If ria_length == ria_pages, 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_pages.
         */
        return ria->ria_length == 0 || ria->ria_length == ria->ria_pages ||
               (idx >= ria->ria_stoff && (idx - ria->ria_stoff) %
                ria->ria_length < ria->ria_pages);
}

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)
{
        struct cl_read_ahead ra = { 0 };
        unsigned long ra_end = 0;
        bool stride_ria;
        pgoff_t page_idx;
        int rc;

        LASSERT(ria);
        RIA_DEBUG(ria);

        stride_ria = ria->ria_length > ria->ria_pages && ria->ria_pages > 0;
        for (page_idx = ria->ria_start;
             page_idx <= ria->ria_end && ria->ria_reserved > 0; page_idx++) {
                if (ras_inside_ra_window(page_idx, ria)) {
                        if (!ra.cra_end || ra.cra_end < page_idx) {
                                unsigned long end;

                                cl_read_ahead_release(env, &ra);

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

                                CDEBUG(D_READA, "idx: %lu, ra: %lu, rpc: %lu\n",
                                       page_idx, ra.cra_end, ra.cra_rpc_size);
                                LASSERTF(ra.cra_end >= page_idx,
                                         "object: %p, indcies %lu / %lu\n",
                                         io->ci_obj, ra.cra_end, page_idx);
                                /*
                                 * update read ahead RPC size.
                                 * NB: it's racy but doesn't matter
                                 */
                                if (ras->ras_rpc_size > ra.cra_rpc_size &&
                                    ra.cra_rpc_size > 0)
                                        ras->ras_rpc_size = ra.cra_rpc_size;
                                /* trim it to align with optimal RPC size */
                                end = ras_align(ras, ria->ria_end + 1, NULL);
                                if (end > 0 && !ria->ria_eof)
                                        ria->ria_end = end - 1;
                                if (ria->ria_end < ria->ria_end_min)
                                        ria->ria_end = ria->ria_end_min;
                                if (ria->ria_end > ra.cra_end)
                                        ria->ria_end = ra.cra_end;
                        }

                        /* If the page is inside the read-ahead window */
                        rc = ll_read_ahead_page(env, io, queue, page_idx);
                        if (rc < 0)
                                break;

                        ra_end = page_idx;
                        if (!rc)
                                ria->ria_reserved--;
                } else if (stride_ria) {
                        /* If it is not in the read-ahead window, and it is
                         * read-ahead mode, then check whether it should skip
                         * the stride gap
                         */
                        pgoff_t offset;
                        /* FIXME: This assertion only is valid when it is for
                         * forward read-ahead, it will be fixed when backward
                         * read-ahead is implemented
                         */
                        LASSERTF(page_idx >= ria->ria_stoff, "Invalid page_idx %lu rs %lu re %lu ro %lu rl %lu rp %lu\n",
                                 page_idx,
                                 ria->ria_start, ria->ria_end, ria->ria_stoff,
                                 ria->ria_length, ria->ria_pages);
                        offset = page_idx - ria->ria_stoff;
                        offset = offset % (ria->ria_length);
                        if (offset > ria->ria_pages) {
                                page_idx += ria->ria_length - offset;
                                CDEBUG(D_READA, "i %lu skip %lu\n", page_idx,
                                       ria->ria_length - offset);
                                continue;
                        }
                }
        }
        cl_read_ahead_release(env, &ra);

        return ra_end;
}

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 vvp_io *vio = vvp_env_io(env);
        struct ll_thread_info *lti = ll_env_info(env);
        struct cl_attr *attr = vvp_env_thread_attr(env);
        unsigned long len, mlen = 0;
        pgoff_t ra_end, start = 0, end = 0;
        struct inode *inode;
        struct ra_io_arg *ria = &lti->lti_ria;
        struct cl_object *clob;
        int ret = 0;
        __u64 kms;

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

        memset(ria, 0, sizeof(*ria));

        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;
        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,
         * 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 = max(ras->ras_next_readahead, ras->ras_stride_offset);
        else
                start = ras->ras_next_readahead;

        if (ras->ras_window_len > 0)
                end = ras->ras_window_start + ras->ras_window_len - 1;

        /* Enlarge the RA window to encompass the full read */
        if (vio->vui_ra_valid &&
            end < vio->vui_ra_start + vio->vui_ra_count - 1)
                end = vio->vui_ra_start + vio->vui_ra_count - 1;

        if (end) {
                unsigned long end_index;

                /* Truncate RA window to end of file */
                end_index = (unsigned long)((kms - 1) >> PAGE_SHIFT);
                if (end_index <= end) {
                        end = end_index;
                        ria->ria_eof = true;
                }

                ras->ras_next_readahead = max(end, end + 1);
                RAS_CDEBUG(ras);
        }
        ria->ria_start = start;
        ria->ria_end = end;
        /* 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_pages = ras->ras_stride_pages;
        }
        spin_unlock(&ras->ras_lock);

        if (end == 0) {
                ll_ra_stats_inc(inode, RA_STAT_ZERO_WINDOW);
                return 0;
        }
        len = ria_page_count(ria);
        if (len == 0) {
                ll_ra_stats_inc(inode, RA_STAT_ZERO_WINDOW);
                return 0;
        }

        CDEBUG(D_READA, DFID ": ria: %lu/%lu, bead: %lu/%lu, hit: %d\n",
               PFID(lu_object_fid(&clob->co_lu)),
               ria->ria_start, ria->ria_end,
               vio->vui_ra_valid ? vio->vui_ra_start : 0,
               vio->vui_ra_valid ? vio->vui_ra_count : 0,
               hit);

        /* at least to extend the readahead window to cover current read */
        if (!hit && vio->vui_ra_valid &&
            vio->vui_ra_start + vio->vui_ra_count > ria->ria_start) {
                unsigned long remainder;

                /* to the end of current read window. */
                mlen = vio->vui_ra_start + vio->vui_ra_count - ria->ria_start;
                /* trim to RPC boundary */
                ras_align(ras, ria->ria_start, &remainder);
                mlen = min(mlen, ras->ras_rpc_size - remainder);
                ria->ria_end_min = ria->ria_start + mlen;
        }

        ria->ria_reserved = ll_ra_count_get(ll_i2sbi(inode), ria, len, mlen);
        if (ria->ria_reserved < len)
                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, len, mlen,
               atomic_read(&ll_i2sbi(inode)->ll_ra_info.ra_cur_pages),
               ll_i2sbi(inode)->ll_ra_info.ra_max_pages);

        ra_end = ll_read_ahead_pages(env, io, queue, ras, ria);

        if (ria->ria_reserved)
                ll_ra_count_put(ll_i2sbi(inode), ria->ria_reserved);

        if (ra_end == end && ra_end == (kms >> PAGE_SHIFT))
                ll_ra_stats_inc(inode, RA_STAT_EOF);

        /* if we didn't get to the end of the region we reserved from
         * the ras we need to go back and update the ras so that the
         * next read-ahead tries from where we left off.  we only do so
         * if the region we failed to issue read-ahead on is still ahead
         * of the app and behind the next index to start read-ahead from
         */
        CDEBUG(D_READA, "ra_end = %lu end = %lu stride end = %lu pages = %d\n",
               ra_end, end, ria->ria_end, ret);

        if (ra_end > 0 && ra_end != end) {
                ll_ra_stats_inc(inode, RA_STAT_FAILED_REACH_END);
                spin_lock(&ras->ras_lock);
                if (ra_end <= ras->ras_next_readahead &&
                    index_in_window(ra_end, ras->ras_window_start, 0,
                                    ras->ras_window_len)) {
                        ras->ras_next_readahead = ra_end + 1;
                        RAS_CDEBUG(ras);
                }
                spin_unlock(&ras->ras_lock);
        }

        return ret;
}

static void ras_set_start(struct inode *inode, struct ll_readahead_state *ras,
                          unsigned long index)
{
        ras->ras_window_start = ras_align(ras, index, NULL);
}

/* called with the ras_lock held or from places where it doesn't matter */
static void ras_reset(struct inode *inode, struct ll_readahead_state *ras,
                      unsigned long index)
{
        ras->ras_last_readpage = index;
        ras->ras_consecutive_requests = 0;
        ras->ras_consecutive_pages = 0;
        ras->ras_window_len = 0;
        ras_set_start(inode, ras, index);
        ras->ras_next_readahead = max(ras->ras_window_start, 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_pages = 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_size = PTLRPC_MAX_BRW_PAGES;
        ras_reset(inode, ras, 0);
        ras->ras_requests = 0;
}

/*
 * Check whether the read request is in the stride window.
 * If it is in the stride window, return 1, otherwise return 0.
 */
static int index_in_stride_window(struct ll_readahead_state *ras,
                                  unsigned long index)
{
        unsigned long stride_gap;

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

        stride_gap = index - ras->ras_last_readpage - 1;

        /* If it is contiguous read */
        if (stride_gap == 0)
                return ras->ras_consecutive_pages + 1 <= ras->ras_stride_pages;

        /* Otherwise check the stride by itself */
        return (ras->ras_stride_length - ras->ras_stride_pages) == stride_gap &&
                ras->ras_consecutive_pages == ras->ras_stride_pages;
}

static void ras_update_stride_detector(struct ll_readahead_state *ras,
                                       unsigned long index)
{
        unsigned long stride_gap = index - ras->ras_last_readpage - 1;

        if ((stride_gap != 0 || ras->ras_consecutive_stride_requests == 0) &&
            !stride_io_mode(ras)) {
                ras->ras_stride_pages = ras->ras_consecutive_pages;
                ras->ras_stride_length = ras->ras_consecutive_pages +
                                         stride_gap;
        }
        LASSERT(ras->ras_request_index == 0);
        LASSERT(ras->ras_consecutive_stride_requests == 0);

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

        ras->ras_stride_pages = ras->ras_consecutive_pages;
        ras->ras_stride_length = stride_gap + ras->ras_consecutive_pages;

        RAS_CDEBUG(ras);
}

/* 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,
                                       unsigned long inc_len)
{
        unsigned long left, step, window_len;
        unsigned long stride_len;

        LASSERT(ras->ras_stride_length > 0);
        LASSERTF(ras->ras_window_start + ras->ras_window_len
                 >= ras->ras_stride_offset, "window_start %lu, window_len %lu stride_offset %lu\n",
                 ras->ras_window_start,
                 ras->ras_window_len, ras->ras_stride_offset);

        stride_len = ras->ras_window_start + ras->ras_window_len -
                     ras->ras_stride_offset;

        left = stride_len % ras->ras_stride_length;
        window_len = ras->ras_window_len - left;

        if (left < ras->ras_stride_pages)
                left += inc_len;
        else
                left = ras->ras_stride_pages + inc_len;

        LASSERT(ras->ras_stride_pages != 0);

        step = left / ras->ras_stride_pages;
        left %= ras->ras_stride_pages;

        window_len += step * ras->ras_stride_length + left;

        if (stride_pg_count(ras->ras_stride_offset, ras->ras_stride_length,
                            ras->ras_stride_pages, ras->ras_stride_offset,
                            window_len) <= ra->ra_max_pages_per_file)
                ras->ras_window_len = window_len;

        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, ras->ras_rpc_size);
        } else {
                unsigned long wlen;

                wlen = min(ras->ras_window_len + ras->ras_rpc_size,
                           ra->ra_max_pages_per_file);
                ras->ras_window_len = ras_align(ras, wlen, NULL);
        }
}

static void ras_update(struct ll_sb_info *sbi, struct inode *inode,
                       struct ll_readahead_state *ras, unsigned long index,
                       enum ras_update_flags flags)
{
        struct ll_ra_info *ra = &sbi->ll_ra_info;
        int zero = 0, stride_detect = 0, ra_miss = 0;
        bool hit = flags & LL_RAS_HIT;

        spin_lock(&ras->ras_lock);

        if (!hit)
                CDEBUG(D_READA, DFID " pages at %lu miss.\n",
                       PFID(ll_inode2fid(inode)), index);

        ll_ra_stats_inc_sbi(sbi, hit ? RA_STAT_HIT : RA_STAT_MISS);

        /* 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 (!index_in_window(index, ras->ras_last_readpage, 8, 8)) {
                zero = 1;
                ll_ra_stats_inc_sbi(sbi, RA_STAT_DISTANT_READPAGE);
        } else if (!hit && ras->ras_window_len &&
                   index < ras->ras_next_readahead &&
                   index_in_window(index, ras->ras_window_start, 0,
                                   ras->ras_window_len)) {
                ra_miss = 1;
                ll_ra_stats_inc_sbi(sbi, RA_STAT_MISS_IN_WINDOW);
        }

        /* 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.  The mmap case does not increment
         * ras_requests and thus can never trigger this behavior.
         */
        if (ras->ras_requests >= 2 && !ras->ras_request_index) {
                __u64 kms_pages;

                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 = 0;
                        ras->ras_next_readahead = index + 1;
                        ras->ras_window_len = min(ra->ra_max_pages_per_file,
                                ra->ra_max_read_ahead_whole_pages);
                        goto out_unlock;
                }
        }
        if (zero) {
                /* check whether it is in stride I/O mode*/
                if (!index_in_stride_window(ras, index)) {
                        if (ras->ras_consecutive_stride_requests == 0 &&
                            ras->ras_request_index == 0) {
                                ras_update_stride_detector(ras, index);
                                ras->ras_consecutive_stride_requests++;
                        } else {
                                ras_stride_reset(ras);
                        }
                        ras_reset(inode, ras, index);
                        ras->ras_consecutive_pages++;
                        goto out_unlock;
                } else {
                        ras->ras_consecutive_pages = 0;
                        ras->ras_consecutive_requests = 0;
                        if (++ras->ras_consecutive_stride_requests > 1)
                                stride_detect = 1;
                        RAS_CDEBUG(ras);
                }
        } else {
                if (ra_miss) {
                        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(inode, 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 <
                                    ras->ras_stride_offset)
                                        ras_stride_reset(ras);
                                RAS_CDEBUG(ras);
                        } else {
                                /* Reset both stride window and normal RA
                                 * window
                                 */
                                ras_reset(inode, ras, index);
                                ras->ras_consecutive_pages++;
                                ras_stride_reset(ras);
                                goto out_unlock;
                        }
                } 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
                         */
                        if (!index_in_stride_window(ras, index)) {
                                /* Shrink stride read-ahead window to be zero */
                                ras_stride_reset(ras);
                                ras->ras_window_len = 0;
                                ras->ras_next_readahead = index;
                        }
                }
        }
        ras->ras_consecutive_pages++;
        ras->ras_last_readpage = index;
        ras_set_start(inode, ras, index);

        if (stride_io_mode(ras)) {
                /* Since stride readahead is sensitive to the offset
                 * of read-ahead, so we use original offset here,
                 * instead of ras_window_start, which is RPC aligned
                 */
                ras->ras_next_readahead = max(index, ras->ras_next_readahead);
                ras->ras_window_start = max(ras->ras_stride_offset,
                                            ras->ras_window_start);
        } else {
                if (ras->ras_next_readahead < ras->ras_window_start)
                        ras->ras_next_readahead = ras->ras_window_start;
                if (!hit)
                        ras->ras_next_readahead = index + 1;
        }
        RAS_CDEBUG(ras);

        /* Trigger RA in the mmap case where ras_consecutive_requests
         * is not incremented and thus can't be used to trigger RA
         */
        if (ras->ras_consecutive_pages >= 4 && flags & LL_RAS_MMAP) {
                ras_increase_window(inode, ras, ra);
                /*
                 * reset consecutive pages so that the readahead window can
                 * grow gradually.
                 */
                ras->ras_consecutive_pages = 0;
                goto out_unlock;
        }

        /* Initially reset the stride window offset to next_readahead*/
        if (ras->ras_consecutive_stride_requests == 2 && stride_detect) {
                /**
                 * Once stride IO mode is detected, next_readahead should be
                 * reset to make sure next_readahead > stride offset
                 */
                ras->ras_next_readahead = max(index, ras->ras_next_readahead);
                ras->ras_stride_offset = index;
                ras->ras_window_start = max(index, ras->ras_window_start);
        }

        /* The initial ras_window_len is set to the request size.  To avoid
         * uselessly reading and discarding pages for random IO the window is
         * only increased once per consecutive request received. */
        if ((ras->ras_consecutive_requests > 1 || stride_detect) &&
            !ras->ras_request_index)
                ras_increase_window(inode, ras, ra);
out_unlock:
        RAS_CDEBUG(ras);
        ras->ras_request_index++;
        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;

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

        LASSERT(ll_i2dtexp(inode));

        env = cl_env_get(&refcheck);
        if (IS_ERR(env)) {
                result = PTR_ERR(env);
                goto out;
        }

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

        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 = cl_offset(clob, vmpage->index);

                /* 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;

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;
        struct ll_sb_info *sbi = ll_i2sbi(inode);
        loff_t start;
        loff_t end;
        enum cl_fsync_mode mode;

        int range_whole = 0;
        int result;
        int ignore_layout = 0;

        if (wbc->range_cyclic) {
                start = 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 (sbi->ll_umounting)
                /* if the mountpoint is being umounted, all pages have to be
                 * evicted to avoid hitting LBUG when truncate_inode_pages()
                 * is called later on.
                 */
                ignore_layout = 1;

        if (!ll_i2info(inode)->lli_clob)
                return 0;

        result = cl_sync_file_range(inode, start, end, mode, ignore_layout);
        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 file *file)
{
        struct ll_file_data *fd = LUSTRE_FPRIVATE(file);
        struct ll_cl_context *lcc;
        struct ll_cl_context *found = NULL;

        read_lock(&fd->fd_lock);
        list_for_each_entry(lcc, &fd->fd_lccs, lcc_list) {
                if (lcc->lcc_cookie == current) {
                        found = lcc;
                        break;
                }
        }
        read_unlock(&fd->fd_lock);

        return found;
}

void ll_cl_add(struct file *file, const struct lu_env *env, struct cl_io *io)
{
        struct ll_file_data *fd = LUSTRE_FPRIVATE(file);
        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;

        write_lock(&fd->fd_lock);
        list_add(&lcc->lcc_list, &fd->fd_lccs);
        write_unlock(&fd->fd_lock);
}

void ll_cl_remove(struct file *file, const struct lu_env *env)
{
        struct ll_file_data *fd = LUSTRE_FPRIVATE(file);
        struct ll_cl_context *lcc = &ll_env_info(env)->lti_io_ctx;

        write_lock(&fd->fd_lock);
        list_del_init(&lcc->lcc_list);
        write_unlock(&fd->fd_lock);
}

static int ll_io_read_page(const struct lu_env *env, struct cl_io *io,
                           struct cl_page *page)
{
        struct inode *inode = vvp_object_inode(page->cp_obj);
        struct ll_file_data *fd = vvp_env_io(env)->vui_fd;
        struct ll_readahead_state *ras = &fd->fd_ras;
        struct cl_2queue *queue  = &io->ci_queue;
        struct ll_sb_info *sbi = ll_i2sbi(inode);
        struct vvp_page *vpg;
        bool uptodate;
        int rc = 0;

        vpg = cl2vvp_page(cl_object_page_slice(page->cp_obj, page));
        uptodate = vpg->vpg_defer_uptodate;

        if (sbi->ll_ra_info.ra_max_pages_per_file > 0 &&
            sbi->ll_ra_info.ra_max_pages > 0) {
                struct vvp_io *vio = vvp_env_io(env);
                enum ras_update_flags flags = 0;

                if (uptodate)
                        flags |= LL_RAS_HIT;
                if (!vio->vui_ra_valid)
                        flags |= LL_RAS_MMAP;
                ras_update(sbi, inode, ras, vvp_index(vpg), flags);
        }

        cl_2queue_init(queue);
        if (uptodate) {
                vpg->vpg_ra_used = 1;
                cl_page_export(env, page, 1);
                cl_page_disown(env, io, page);
        } else {
                cl_page_list_add(&queue->c2_qin, page);
        }

        if (sbi->ll_ra_info.ra_max_pages_per_file > 0 &&
            sbi->ll_ra_info.ra_max_pages > 0) {
                int rc2;

                rc2 = ll_readahead(env, io, &queue->c2_qin, ras,
                                   uptodate);
                CDEBUG(D_READA, DFID "%d pages read ahead at %lu\n",
                       PFID(ll_inode2fid(inode)), rc2, vvp_index(vpg));
        }

        if (queue->c2_qin.pl_nr > 0)
                rc = cl_io_submit_rw(env, io, CRT_READ, queue);

        /*
         * Unlock unsent pages in case of error.
         */
        cl_page_list_disown(env, io, &queue->c2_qin);
        cl_2queue_fini(env, queue);

        return rc;
}

int ll_readpage(struct file *file, struct page *vmpage)
{
        struct cl_object *clob = ll_i2info(file_inode(file))->lli_clob;
        struct ll_cl_context *lcc;
        const struct lu_env  *env;
        struct cl_io   *io;
        struct cl_page *page;
        int result;

        lcc = ll_cl_find(file);
        if (!lcc) {
                unlock_page(vmpage);
                return -EIO;
        }

        env = lcc->lcc_env;
        io = lcc->lcc_io;
        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);
                } 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);
        }
        return result;
}

int ll_page_sync_io(const struct lu_env *env, struct cl_io *io,
                    struct cl_page *page, enum cl_req_type crt)
{
        struct cl_2queue  *queue;
        int result;

        LASSERT(io->ci_type == CIT_READ || io->ci_type == CIT_WRITE);

        queue = &io->ci_queue;
        cl_2queue_init_page(queue, page);

        result = cl_io_submit_sync(env, io, crt, queue, 0);
        LASSERT(cl_page_is_owned(page, io));

        if (crt == CRT_READ)
                /*
                 * in CRT_WRITE case page is left locked even in case of
                 * error.
                 */
                cl_page_list_disown(env, io, &queue->c2_qin);
        cl_2queue_fini(env, queue);

        return result;
}