Date:   Tue, 14 Aug 2018 19:15:24 -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 08/15, Chao Yu wrote:
> On 2018/8/15 1:28, Jaegeuk Kim wrote:
> > On 08/14, Chao Yu wrote:
> >> On 2018/8/14 12:04, Jaegeuk Kim wrote:
> >>> 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.
> >>
> >> Yeah, but in reality, there would be more threads competing in same log header,
> >> so I worry that the effect of defragmenting will not so good as we expect,
> >> anyway, for benchmark, it's enough.
> > 
> > Basically, I think this is not a benchmark issue. :) It just reveals the issue
> > much easily. Let me think about three cases:
> > 1) WB_SYNC_NONE & WB_SYNC_NONE
> >  -> can simply use mutex_lock
> > 
> > 2) WB_SYNC_ALL & WB_SYNC_NONE
> >  -> can use mutex_lock on WB_SYNC_ALL having >512 blocks, while WB_SYNC_NONE
> >     will skip writing blocks
> > 
> > 3) WB_SYNC_ALL & WB_SYNC_ALL
> >  -> can use mutex_lock on WB_SYNC_ALL having >512 blocks, in order to avoid
> >     starvation.
> > 
> > 
> > I've been testing the below.
> > 
> > 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;
> 
> Just cover buffered IO? how about covering Direct IO and atomic write as well?

I'd expect direct IO does in-place-updates, and not sure whether we need to
add another lock contention between buffered or direct IO. Atomic writes
would be covered by ->min_seq_blocks.

> 
> Thanks,
> 
> > }
> > 
> > Thanks,
> > 
> >>
> >> Thanks,
> >>
> >>>
> >>>>
> >>>> 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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