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

[Jeuk Kim <jeuk20.kim@gmail.com>]

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)
-- 
2.43.0