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SubjectRe: [f2fs-dev] [PATCH v3] f2fs: fix performance issue observed with multi-thread sequential read
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Hi Jaegeuk,

On 2018/8/11 2:56, Jaegeuk Kim wrote:
> 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).

IMO, it only impact sequential read performance in a large file which may be
fragmented during multi-thread writing.

In android environment, mostly, the large file should be cold type, such as apk,
mp3, rmvb, jpeg..., so I think we only need to serialize writepages() for cold
data area writer.

So how about adding a mount option to serialize writepage() for different type
of log, e.g. in android, using serialize=4; by default, using serialize=7
HOT_DATA 1
WARM_DATA 2
COLD_DATA 4

Thanks,

>
> Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
> ---
> Changelog from v2:
> - fix deadlock in f2fs_gc
>
> fs/f2fs/data.c | 9 +++++++++
> fs/f2fs/f2fs.h | 1 +
> fs/f2fs/super.c | 1 +
> 3 files changed, 11 insertions(+)
>
> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> index 45f043ee48bd..9f0149cdeed8 100644
> --- a/fs/f2fs/data.c
> +++ b/fs/f2fs/data.c
> @@ -2132,6 +2132,7 @@ 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)
> @@ -2162,10 +2163,18 @@ 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)) {
> + 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 b1c127d8383b..29bbc55cbc0b 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -1133,6 +1133,7 @@ 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/super.c b/fs/f2fs/super.c
> index be41dbd7b261..53d70b64fea1 100644
> --- a/fs/f2fs/super.c
> +++ b/fs/f2fs/super.c
> @@ -2842,6 +2842,7 @@ 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);
>

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