Date:   Tue, 14 Aug 2018 11:49:00 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
CC:     <linux-kernel@...r.kernel.org>,
        <linux-f2fs-devel@...ts.sourceforge.net>
Subject: Re: [f2fs-dev] [PATCH v3] f2fs: fix performance issue observed with
 multi-thread sequential read

On 2018/8/14 4:11, Jaegeuk Kim wrote:
> On 08/13, Chao Yu wrote:
>> 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
> 
> Well, I don't think we need to give too many mount options for this fragmented
> case. How about doing this for the large files only like this?

Thread A write 512 pages			Thread B write 8 pages

- writepages()
 - mutex_lock(&sbi->writepages);
  - writepage();
...
						- writepages()
						 - writepage()
						  ....
  - writepage();
...
 - mutex_unlock(&sbi->writepages);

Above case will also cause fragmentation since we didn't serialize all
concurrent IO with the lock.

Do we need to consider such case?

Thanks,

> 
>>>From 4fea0b6e4da8512a72dd52afc7a51beb35966ad9 Mon Sep 17 00:00:00 2001
> From: Jaegeuk Kim <jaegeuk@...nel.org>
> Date: Thu, 9 Aug 2018 17:53:34 -0700
> Subject: [PATCH] f2fs: fix performance issue observed with multi-thread
>  sequential read
> 
> 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 <stummala@...eaurora.org>
> Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
> ---
>  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" <jaegeuk@...nel.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" <jaegeuk@...nel.org>
> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> index 45f043ee48bd..f09231b1cc74 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 +2163,19 @@ 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) &&
> +			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 375aa9f30cfa..098bdedc28bf 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 63fc647f9ac2..ffea2d1303bd 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -4131,6 +4131,7 @@ 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 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);
> 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),
> 

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