Re: [f2fs-dev] [PATCH v3] f2fs: fix performance issue observed with multi-thread sequential read

[Chao Yu]

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?

Thanks,

> }
> 
> Thanks,
> 
>>
>> Thanks,
>>
>>>
>>>>
>>>> Thanks,
>>>>
>>>>>
>>>>> >From 4fea0b6e4da8512a72dd52afc7a51beb35966ad9 Mon Sep 17 00:00:00 2001
>>>>> From: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
>>>>> 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@xxxxxxxxxxxxxx>
>>>>> Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
>>>>> ---
>>>>>  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@xxxxxxxxxx>
>>>>> +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@xxxxxxxxxx>
>>>>> 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),
>>>>>
>>>
>>> .
>>>
> 
> .
>