linux-kernel - [PATCH v2] f2fs: optimize f2fs_overwrite_io() for f2fs_iomap

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Message-ID: <20260122104527.416871-1-youngjin.gil@samsung.com>
Date: Thu, 22 Jan 2026 19:45:27 +0900
From: Yeongjin Gil <youngjin.gil@...sung.com>
To: jaegeuk@...nel.org, chao@...nel.org, jyh429@...il.com,
	linux-f2fs-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Cc: Yeongjin Gil <youngjin.gil@...sung.com>, Sungjong Seo
	<sj1557.seo@...sung.com>, Sunmin Jeong <s_min.jeong@...sung.com>
Subject: [PATCH v2] f2fs: optimize f2fs_overwrite_io() for f2fs_iomap_begin

When overwriting already allocated blocks, f2fs_iomap_begin() calls
f2fs_overwrite_io() to check block mappings. However,
f2fs_overwrite_io() iterates through all mapped blocks in the range,
which can be inefficient for fragmented files with large I/O requests.

This patch optimizes f2fs_overwrite_io() by adding a 'check_first'
parameter and introducing __f2fs_overwrite_io() helper. When called from
f2fs_iomap_begin(), we only check the first mapping to determine if the
range is already allocated, which is sufficient for setting
map.m_may_create.

This optimization significantly reduces the number of f2fs_map_blocks()
calls in f2fs_overwrite_io() when called from f2fs_iomap_begin(),
especially for fragmented files with large I/O requests.

Fixes: 351bc761338d ("f2fs: optimize f2fs DIO overwrites")
Reviewed-by: Sungjong Seo <sj1557.seo@...sung.com>
Reviewed-by: Sunmin Jeong <s_min.jeong@...sung.com>
Signed-off-by: Yeongjin Gil <youngjin.gil@...sung.com>
---
 fs/f2fs/data.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 2e133a723b99..11c262afad65 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -1851,7 +1851,8 @@ int f2fs_map_blocks(struct inode *inode, struct f2fs_map_blocks *map, int flag)
 	return err;
 }
 
-bool f2fs_overwrite_io(struct inode *inode, loff_t pos, size_t len)
+static bool __f2fs_overwrite_io(struct inode *inode, loff_t pos, size_t len,
+				bool check_first)
 {
 	struct f2fs_map_blocks map;
 	block_t last_lblk;
@@ -1873,10 +1874,17 @@ bool f2fs_overwrite_io(struct inode *inode, loff_t pos, size_t len)
 		if (err || map.m_len == 0)
 			return false;
 		map.m_lblk += map.m_len;
+		if (check_first)
+			break;
 	}
 	return true;
 }
 
+bool f2fs_overwrite_io(struct inode *inode, loff_t pos, size_t len)
+{
+	return __f2fs_overwrite_io(inode, pos, len, false);
+}
+
 static int f2fs_xattr_fiemap(struct inode *inode,
 				struct fiemap_extent_info *fieinfo)
 {
@@ -4443,7 +4451,7 @@ static int f2fs_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
 	 * f2fs_map_lock and f2fs_balance_fs are not necessary.
 	 */
 	if ((flags & IOMAP_WRITE) &&
-		!f2fs_overwrite_io(inode, offset, length))
+		!__f2fs_overwrite_io(inode, offset, length, true))
 		map.m_may_create = true;
 
 	err = f2fs_map_blocks(inode, &map, F2FS_GET_BLOCK_DIO);
-- 
2.43.0