This reverts the commit - "b93f771 - f2fs: remove writepages lock"
to fix the drop in sequential read throughput.

Test: ./tiotest -t 32 -d /data/tio_tmp -f 32 -b 524288 -k 1 -k 3 -L
device: UFS

Before -
read throughput: 185 MB/s
total read requests: 85177 (of these ~80000 are 4KB size requests).
total write requests: 2546 (of these ~2208 requests are written in 512KB).

After -
read throughput: 758 MB/s
total read requests: 2417 (of these ~2042 are 512KB reads).
total write requests: 2701 (of these ~2034 requests are written in 512KB).

Signed-off-by: Sahitya Tummala <stumm...@codeaurora.org>
Signed-off-by: Jaegeuk Kim <jaeg...@kernel.org>
---

Change log from v3:
 - add more conditions to serialize the allocation

 Documentation/ABI/testing/sysfs-fs-f2fs |  8 ++++++++
 fs/f2fs/data.c                          | 10 ++++++++++
 fs/f2fs/f2fs.h                          |  2 ++
 fs/f2fs/segment.c                       |  1 +
 fs/f2fs/super.c                         |  1 +
 fs/f2fs/sysfs.c                         |  2 ++
 6 files changed, 24 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-fs-f2fs 
b/Documentation/ABI/testing/sysfs-fs-f2fs
index 9b0123388f18..94a24aedcdb2 100644
--- a/Documentation/ABI/testing/sysfs-fs-f2fs
+++ b/Documentation/ABI/testing/sysfs-fs-f2fs
@@ -51,6 +51,14 @@ Description:
                 Controls the dirty page count condition for the in-place-update
                 policies.
 
+What:          /sys/fs/f2fs/<disk>/min_seq_blocks
+Date:          August 2018
+Contact:       "Jaegeuk Kim" <jaeg...@kernel.org>
+Description:
+                Controls the dirty page count condition for batched sequential
+                writes in ->writepages.
+
+
 What:          /sys/fs/f2fs/<disk>/min_hot_blocks
 Date:          March 2017
 Contact:       "Jaegeuk Kim" <jaeg...@kernel.org>
diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 43d3723dc886..fb63425ea242 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -2130,6 +2130,7 @@ static int __f2fs_write_data_pages(struct address_space 
*mapping,
        struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
        struct blk_plug plug;
        int ret;
+       bool locked = false;
 
        /* deal with chardevs and other special file */
        if (!mapping->a_ops->writepage)
@@ -2160,10 +2161,19 @@ static int __f2fs_write_data_pages(struct address_space 
*mapping,
        else if (atomic_read(&sbi->wb_sync_req[DATA]))
                goto skip_write;
 
+       if (!S_ISDIR(inode->i_mode) && (wbc->sync_mode != WB_SYNC_ALL ||
+                       get_dirty_pages(inode) <= SM_I(sbi)->min_seq_blocks)) {
+               mutex_lock(&sbi->writepages);
+               locked = true;
+       }
+
        blk_start_plug(&plug);
        ret = f2fs_write_cache_pages(mapping, wbc, io_type);
        blk_finish_plug(&plug);
 
+       if (locked)
+               mutex_unlock(&sbi->writepages);
+
        if (wbc->sync_mode == WB_SYNC_ALL)
                atomic_dec(&sbi->wb_sync_req[DATA]);
        /*
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 9a6ba4a8d338..170573f8a04a 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -913,6 +913,7 @@ struct f2fs_sm_info {
        unsigned int ipu_policy;        /* in-place-update policy */
        unsigned int min_ipu_util;      /* in-place-update threshold */
        unsigned int min_fsync_blocks;  /* threshold for fsync */
+       unsigned int min_seq_blocks;    /* threshold for sequential blocks */
        unsigned int min_hot_blocks;    /* threshold for hot block allocation */
        unsigned int min_ssr_sections;  /* threshold to trigger SSR allocation 
*/
 
@@ -1133,6 +1134,7 @@ struct f2fs_sb_info {
        struct rw_semaphore sb_lock;            /* lock for raw super block */
        int valid_super_block;                  /* valid super block no */
        unsigned long s_flag;                           /* flags for sbi */
+       struct mutex writepages;                /* mutex for writepages() */
 
 #ifdef CONFIG_BLK_DEV_ZONED
        unsigned int blocks_per_blkz;           /* F2FS blocks per zone */
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index b136e39e1e9e..20650e25117b 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -4127,6 +4127,7 @@ int f2fs_build_segment_manager(struct f2fs_sb_info *sbi)
                sm_info->ipu_policy = 1 << F2FS_IPU_FSYNC;
        sm_info->min_ipu_util = DEF_MIN_IPU_UTIL;
        sm_info->min_fsync_blocks = DEF_MIN_FSYNC_BLOCKS;
+       sm_info->min_seq_blocks = sbi->blocks_per_seg * sbi->segs_per_sec;
        sm_info->min_hot_blocks = DEF_MIN_HOT_BLOCKS;
        sm_info->min_ssr_sections = reserved_sections(sbi);
 
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index c6e4750a9187..6b6cb4eb8439 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -2864,6 +2864,7 @@ static int f2fs_fill_super(struct super_block *sb, void 
*data, int silent)
        /* init f2fs-specific super block info */
        sbi->valid_super_block = valid_super_block;
        mutex_init(&sbi->gc_mutex);
+       mutex_init(&sbi->writepages);
        mutex_init(&sbi->cp_mutex);
        init_rwsem(&sbi->node_write);
        init_rwsem(&sbi->node_change);
diff --git a/fs/f2fs/sysfs.c b/fs/f2fs/sysfs.c
index cd2e030e47b8..81c0e5337443 100644
--- a/fs/f2fs/sysfs.c
+++ b/fs/f2fs/sysfs.c
@@ -397,6 +397,7 @@ F2FS_RW_ATTR(SM_INFO, f2fs_sm_info, batched_trim_sections, 
trim_sections);
 F2FS_RW_ATTR(SM_INFO, f2fs_sm_info, ipu_policy, ipu_policy);
 F2FS_RW_ATTR(SM_INFO, f2fs_sm_info, min_ipu_util, min_ipu_util);
 F2FS_RW_ATTR(SM_INFO, f2fs_sm_info, min_fsync_blocks, min_fsync_blocks);
+F2FS_RW_ATTR(SM_INFO, f2fs_sm_info, min_seq_blocks, min_seq_blocks);
 F2FS_RW_ATTR(SM_INFO, f2fs_sm_info, min_hot_blocks, min_hot_blocks);
 F2FS_RW_ATTR(SM_INFO, f2fs_sm_info, min_ssr_sections, min_ssr_sections);
 F2FS_RW_ATTR(NM_INFO, f2fs_nm_info, ram_thresh, ram_thresh);
@@ -449,6 +450,7 @@ static struct attribute *f2fs_attrs[] = {
        ATTR_LIST(ipu_policy),
        ATTR_LIST(min_ipu_util),
        ATTR_LIST(min_fsync_blocks),
+       ATTR_LIST(min_seq_blocks),
        ATTR_LIST(min_hot_blocks),
        ATTR_LIST(min_ssr_sections),
        ATTR_LIST(max_victim_search),
-- 
2.17.0.441.gb46fe60e1d-goog


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