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

[Chao Yu <chao@kernel.org>]

On 10/16/2025 1:16 PM, Jeuk Kim wrote:
> From: Jeuk Kim <jeuk20.kim@samsung.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@samsung.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,