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@samsung.com>
Reviewed-by: Sunmin Jeong <s_min.jeong@samsung.com>
Signed-off-by: Yeongjin Gil <youngjin.gil@samsung.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

On 1/22/2026 6:45 PM, Yeongjin Gil wrote:
> 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.
> 

Cc: stable@kernel.org

> Fixes: 351bc761338d ("f2fs: optimize f2fs DIO overwrites")
> Reviewed-by: Sungjong Seo <sj1557.seo@samsung.com>
> Reviewed-by: Sunmin Jeong <s_min.jeong@samsung.com>
> Signed-off-by: Yeongjin Gil <youngjin.gil@samsung.com>

Otherwise, it looks good to me.

Reviewed-by: Chao Yu <chao@kernel.org>

Thanks,

> ---
>   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);