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

From: Chao Yu
Date: Tue Aug 14 2018 - 23:45:05 EST

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On 2018/8/15 10:15, Jaegeuk Kim wrote:
> 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

For initial writes, they are not IPU.

> add another lock contention between buffered or direct IO. Atomic writes
> would be covered by ->min_seq_blocks.

Okay. :)

Thanks,

>
>>
>> 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),
>>>>>>>
>>>>>
>>>>> .
>>>>>
>>>
>>> .
>>>
>
> .
>

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