Date:   Mon, 13 Aug 2018 21:04:34 -0700
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Chao Yu <yuchao0@...wei.com>
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 08/14, Chao Yu wrote:
> 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?

We can simply allow 512 and 8 in the same segment, which would not a big deal,
when considering starvation of Thread B.

> 
> 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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