linux-kernel - Re: [PATCH] f2fs: serialize writeback for inline-crypto inodes

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Message-ID: <a4bcf251-e1cf-47ef-84df-5c43b2b288c0@gmail.com>
Date: Tue, 21 Oct 2025 16:12:18 +0900
From: Jeuk Kim <jeuk20.kim@...il.com>
To: Chao Yu <chao@...nel.org>, jaegeuk@...nel.org
Cc: linux-f2fs-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
 jeuk20.kim@...sung.com, d_hyun.kwon@...sung.com, gyusun.lee@...sung.com,
 hyenc.jeong@...sung.com, j-young.choi@...sung.com, jaemyung.lee@...sung.com,
 jieon.seol@...sung.com, keosung.park@...sung.com, wone.jung@...sung.com
Subject: Re: [PATCH] f2fs: serialize writeback for inline-crypto inodes


On 10/21/2025 3:51 PM, Chao Yu wrote:
> On 10/21/25 11:33, Jeuk Kim wrote:
>> On 10/16/2025 7:12 PM, Chao Yu wrote:
>>> On 10/16/2025 1:16 PM, Jeuk Kim wrote:
>>>> From: Jeuk Kim <jeuk20.kim@...sung.com>
>>>>
>>>> Inline encryption derives DUN from <inode, file offset>,
>>>> so bios from different inodes can't merge. With multi-threaded
>>>> buffered O_SYNC writes where each thread writes to its own file,
>>>> 4KiB-per-page LBA allocation interleaves across inodes and
>>>> causes bio split. Serialize writeback for fscrypt inline-crypto
>>>> inodes via __should_serialize_io() to keep foreground writeback
>>>> focused on one inode and avoid split.
>>>>
>>>> Test: fio --name=wb_osync --rw=write --bs=1M \
>>>>         --time_based=1 --runtime=60s --size=2G \
>>>>         --ioengine=psync --direct=0 --sync=1 \
>>>>         --numjobs=8 --thread=1 --nrfiles=1 \
>>>>         --filename_format='wb_osync.$jobnum'
>>>>
>>>> device: UFS
>>>>
>>>> Before -
>>>>     write throughput: 675MiB/s
>>>>     device I/O size distribution (by count, total 1027414):
>>>>       4 KiB:  923139 (89.9%)
>>>>       8 KiB:  84798 (8.3%)
>>>>       ≥512 KiB: 453 (0.0%)
>>>>
>>>> After -
>>>>     write throughput: 1760MiB/s
>>>>     device I/O size distribution (by count, total 231750):
>>>>       4 KiB:  16904 (7.3%)
>>>>       8 KiB:  72128 (31.1%)
>>>>       ≥512 KiB: 118900 (51.3%)
>>>>
>>>> Signed-off-by: Jeuk Kim <jeuk20.kim@...sung.com>
>>>> ---
>>>>    fs/f2fs/data.c | 2 ++
>>>>    1 file changed, 2 insertions(+)
>>>>
>>>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
>>>> index ef38e62cda8f..ae6fb435d576 100644
>>>> --- a/fs/f2fs/data.c
>>>> +++ b/fs/f2fs/data.c
>>>> @@ -3217,6 +3217,8 @@ static inline bool __should_serialize_io(struct inode *inode,
>>>>          if (f2fs_need_compress_data(inode))
>>>>            return true;
>>>> +    if (fscrypt_inode_uses_inline_crypto(inode))
>>>> +        return true;
>>>>        if (wbc->sync_mode != WB_SYNC_ALL)
>>>>            return true;
>>>>        if (get_dirty_pages(inode) >= SM_I(F2FS_I_SB(inode))->min_seq_blocks)
>>> Jeuk,
>>>
>>> Can you please try tuning /sys/fs/f2fs/<dev>/min_seq_blocks to see whether it
>>> can achive the goal?
>>>
>>> Thanks,
>>>
>> Hi Chao,
>>
>> Thanks a lot for the suggestion.
>> I tried tuning `/sys/fs/f2fs/<dev>/min_seq_blocks` as you mentioned, and it also achieved similar performance improvement on my setup.
>>
>> Your approach looks cleaner and better than the one I proposed.
>>
>>  From what I see, even after reducing this value from the default (2MB) to 512 KB on my local system, there doesn’t seem to be any noticeable performance drop or other side effects.
>> Do you see any possible downsides with lowering this value that I might have missed?
> Hi Jeuk,
>
> We're using sbi->writepages to serialize large IOs, once you tuned default
> value from 2MB to 512KB, in Android, there are threads issue [512K, 2M)
> sized IOs, they will join into racing on grabbing the .writepages lock,
> I guess that will cause potential performance regression, right?

That's right, that could happen.

I’ll run some tests to check that, including a few other cases that 
might be affected.
I’ll share the results here if I find anything noticeable.

Thanks for your help!

> Thanks,
>