linux-kernel - Re: [f2fs-dev] [PATCH 2/2] f2fs: avoid IO split due to mixed WB_SYNC_ALL and WB_SYNC

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Message-ID: <bf61ab56-b3be-990d-01c3-ce9273fb47b5@huawei.com>
Date:   Fri, 31 Mar 2017 11:51:11 +0800
From:   heyunlei <heyunlei@...wei.com>
To:     Jaegeuk Kim <jaegeuk@...nel.org>, <linux-kernel@...r.kernel.org>,
        <linux-fsdevel@...r.kernel.org>,
        <linux-f2fs-devel@...ts.sourceforge.net>
Subject: Re: [f2fs-dev] [PATCH 2/2] f2fs: avoid IO split due to mixed
 WB_SYNC_ALL and WB_SYNC_NONE

Hi Jaegeuk,

Can we split in place update bios into single sbi->f2fs_bio_info for more page
merged in out place update? This case can be show as below:

in place update submit a bio with one page
	out place update submit a bio with one page
in place update submit a bio with one page
	out place update submit a bio with one page
... ...

just like WB_SYNC_ALL and WB_SYNC_NONE case.

Thanks.

On 2017/3/30 4:48, Jaegeuk Kim wrote:
> If two threads try to flush dirty pages in different inodes respectively,
> f2fs_write_data_pages() will produce WRITE and WRITE_SYNC one at a time,
> resulting in a lot of 4KB seperated IOs.
>
> So, this patch gives higher priority to WB_SYNC_ALL IOs and gathers write
> IOs with a big WRITE_SYNC'ed bio.
>
> Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
> ---
>  fs/f2fs/data.c  | 15 +++++++++++++--
>  fs/f2fs/f2fs.h  |  3 +++
>  fs/f2fs/super.c |  2 ++
>  3 files changed, 18 insertions(+), 2 deletions(-)
>
> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> index 8f36080b47c4..b1cac6d85bcb 100644
> --- a/fs/f2fs/data.c
> +++ b/fs/f2fs/data.c
> @@ -1605,8 +1605,10 @@ static int f2fs_write_cache_pages(struct address_space *mapping,
>  				last_idx = page->index;
>  			}
>
> -			if (--wbc->nr_to_write <= 0 &&
> -			    wbc->sync_mode == WB_SYNC_NONE) {
> +			/* give a priority to WB_SYNC threads */
> +			if ((atomic_read(&F2FS_M_SB(mapping)->wb_sync_req) ||
> +					--wbc->nr_to_write <= 0) &&
> +					wbc->sync_mode == WB_SYNC_NONE) {
>  				done = 1;
>  				break;
>  			}
> @@ -1662,9 +1664,18 @@ static int f2fs_write_data_pages(struct address_space *mapping,
>
>  	trace_f2fs_writepages(mapping->host, wbc, DATA);
>
> +	/* to avoid spliting IOs due to mixed WB_SYNC_ALL and WB_SYNC_NONE */
> +	if (wbc->sync_mode == WB_SYNC_ALL)
> +		atomic_inc(&sbi->wb_sync_req);
> +	else if (atomic_read(&sbi->wb_sync_req))
> +		goto skip_write;
> +
>  	blk_start_plug(&plug);
>  	ret = f2fs_write_cache_pages(mapping, wbc);
>  	blk_finish_plug(&plug);
> +
> +	if (wbc->sync_mode == WB_SYNC_ALL)
> +		atomic_dec(&sbi->wb_sync_req);
>  	/*
>  	 * if some pages were truncated, we cannot guarantee its mapping->host
>  	 * to detect pending bios.
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index 32d6f674c114..fd39db681226 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -888,6 +888,9 @@ struct f2fs_sb_info {
>  	/* # of allocated blocks */
>  	struct percpu_counter alloc_valid_block_count;
>
> +	/* writeback control */
> +	atomic_t wb_sync_req;			/* count # of WB_SYNC threads */
> +
>  	/* valid inode count */
>  	struct percpu_counter total_valid_inode_count;
>
> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
> index 2d78f3c76d18..cb65e6d0d275 100644
> --- a/fs/f2fs/super.c
> +++ b/fs/f2fs/super.c
> @@ -1566,6 +1566,8 @@ static void init_sb_info(struct f2fs_sb_info *sbi)
>  	for (i = 0; i < NR_COUNT_TYPE; i++)
>  		atomic_set(&sbi->nr_pages[i], 0);
>
> +	atomic_set(&sbi->wb_sync_req, 0);
> +
>  	INIT_LIST_HEAD(&sbi->s_list);
>  	mutex_init(&sbi->umount_mutex);
>  	mutex_init(&sbi->wio_mutex[NODE]);
>