linux-kernel - [PATCH v4] f2fs: readahead node blocks in F2FS_GET_BLOCK

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Message-Id: <20250924074358.253759-1-yunji0.kang@samsung.com>
Date: Wed, 24 Sep 2025 16:43:58 +0900
From: Yunji Kang <yunji0.kang@...sung.com>
To: jaegeuk@...nel.org, chao@...nel.org
Cc: linux-f2fs-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
	Yunji Kang <yunji0.kang@...sung.com>, Sungjong Seo <sj1557.seo@...sung.com>,
	Sunmin Jeong <s_min.jeong@...sung.com>
Subject: [PATCH v4] f2fs: readahead node blocks in F2FS_GET_BLOCK_PRECACHE
 mode

In f2fs_precache_extents(), For large files, It requires reading many
node blocks. Instead of reading each node block with synchronous I/O,
this patch applies readahead so that node blocks can be fetched in
advance.

It reduces the overhead of repeated sync reads and improves efficiency
when precaching extents of large files.

I created a file with the same largest extent and executed the test.
For this experiment, I set the file's largest extent with an offset of 0
and a size of 1GB. I configured the remaining area with 100MB extents.

5GB test file:
dd if=/dev/urandom of=test1 bs=1m count=5120
cp test1 test2
fsync test1
dd if=test1 of=test2 bs=1m skip=1024 seek=1024 count=100 conv=notrunc
dd if=test1 of=test2 bs=1m skip=1224 seek=1224 count=100 conv=notrunc
...
dd if=test1 of=test2 bs=1m skip=5024 seek=5024 count=100 conv=notrunc
reboot

I also created 10GB and 20GB files with large extents using the same
method.

ioctl(F2FS_IOC_PRECACHE_EXTENTS) test results are as follows:
  +-----------+---------+---------+-----------+
  | File size | Before  | After   | Reduction |
  +-----------+---------+---------+-----------+
  | 5GB       | 101.8ms | 37.0ms  | 72.1%     |
  | 10GB      | 222.9ms | 56.0ms  | 74.9%     |
  | 20GB      | 446.2ms | 116.4ms | 73.9%     |
  +-----------+---------+---------+-----------+
Tested on a 256GB mobile device with an SM8750 chipset.

Reviewed-by: Sungjong Seo <sj1557.seo@...sung.com>
Reviewed-by: Sunmin Jeong <s_min.jeong@...sung.com>
Signed-off-by: Yunji Kang <yunji0.kang@...sung.com>
---
v2:
 - Modify the readahead condition check routine for better code
readability.
 - Update the title from 'node block' to 'node blocks'.

v3:
 - Bug fix to allow more node pages to be readahead.
 - Updated with test results.

v4:
 - Removed a specific condition for precache, 
as using the existing mode (LOOKUP_NODE_RA) is sufficient.

 fs/f2fs/data.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 7961e0ddfca3..a20a99d7ba5b 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -1572,6 +1572,9 @@ int f2fs_map_blocks(struct inode *inode, struct f2fs_map_blocks *map, int flag)
 	pgofs =	(pgoff_t)map->m_lblk;
 	end = pgofs + maxblocks;

+	if (flag == F2FS_GET_BLOCK_PRECACHE)
+		mode = LOOKUP_NODE_RA;
+
 next_dnode:
 	if (map->m_may_create) {
 		if (f2fs_lfs_mode(sbi))
-- 
2.34.1