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

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Message-Id: <20250917055217.39960-1-yunji0.kang@samsung.com>
Date: Wed, 17 Sep 2025 14:52:17 +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] f2fs: readahead node block 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 | 72.1ms  | 29.2%     |
  | 10GB      | 222.9ms | 149.5ms | 32.9%     |
  | 20GB      | 446.2ms | 276.3ms | 38.1%     |
  +-----------+---------+---------+-----------+
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>
---
 fs/f2fs/data.c | 3 +++
 fs/f2fs/f2fs.h | 1 +
 fs/f2fs/node.c | 4 +++-
 3 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 7961e0ddfca3..ab3117e3b24a 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_PRECACHE;
+
 next_dnode:
 	if (map->m_may_create) {
 		if (f2fs_lfs_mode(sbi))
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 9d3bc9633c1d..3ce41528d48e 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -651,6 +651,7 @@ enum {
 					 * look up a node with readahead called
 					 * by get_data_block.
 					 */
+	LOOKUP_NODE_PRECACHE,		/* look up a node for F2FS_GET_BLOCK_PRECACHE */
 };
 
 #define DEFAULT_RETRY_IO_COUNT	8	/* maximum retry read IO or flush count */
diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
index 4254db453b2d..50be167e5c59 100644
--- a/fs/f2fs/node.c
+++ b/fs/f2fs/node.c
@@ -860,7 +860,9 @@ int f2fs_get_dnode_of_data(struct dnode_of_data *dn, pgoff_t index, int mode)
 			set_nid(parent, offset[i - 1], nids[i], i == 1);
 			f2fs_alloc_nid_done(sbi, nids[i]);
 			done = true;
-		} else if (mode == LOOKUP_NODE_RA && i == level && level > 1) {
+		} else if ((mode == LOOKUP_NODE_RA ||
+				(mode == LOOKUP_NODE_PRECACHE && offset[i - 1] % MAX_RA_NODE == 0))
+				&& i == level && level > 1) {
 			nfolio[i] = f2fs_get_node_folio_ra(parent, offset[i - 1]);
 			if (IS_ERR(nfolio[i])) {
 				err = PTR_ERR(nfolio[i]);
-- 
2.34.1