linux-kernel - [PATCH v3 04/14] ext4: correct the mapping status if the extent has been zeroed

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Message-ID: <20251129103247.686136-5-yi.zhang@huaweicloud.com>
Date: Sat, 29 Nov 2025 18:32:36 +0800
From: Zhang Yi <yi.zhang@...weicloud.com>
To: linux-ext4@...r.kernel.org
Cc: linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	tytso@....edu,
	adilger.kernel@...ger.ca,
	jack@...e.cz,
	ojaswin@...ux.ibm.com,
	yi.zhang@...wei.com,
	yi.zhang@...weicloud.com,
	yizhang089@...il.com,
	libaokun1@...wei.com,
	yangerkun@...wei.com
Subject: [PATCH v3 04/14] ext4: correct the mapping status if the extent has been zeroed

From: Zhang Yi <yi.zhang@...wei.com>

Before submitting I/O and allocating blocks with the
EXT4_GET_BLOCKS_PRE_IO flag set, ext4_split_convert_extents() may
convert the target extent range to initialized due to ENOSPC, ENOMEM, or
EQUOTA errors. However, it still marks the mapping as incorrectly
unwritten. Although this may not seem to cause any practical problems,
it will result in an unnecessary extent conversion operation after I/O
completion. Therefore, it's better to correct the returned mapping
status.

Signed-off-by: Zhang Yi <yi.zhang@...wei.com>
Reviewed-by: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
Reviewed-by: Baokun Li <libaokun1@...wei.com>
---
 fs/ext4/extents.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 91b56de60c90..daecf3f0b367 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -3933,6 +3933,8 @@ ext4_ext_handle_unwritten_extents(handle_t *handle, struct inode *inode,
 
 	/* get_block() before submitting IO, split the extent */
 	if (flags & EXT4_GET_BLOCKS_SPLIT_NOMERGE) {
+		int depth;
+
 		path = ext4_split_convert_extents(handle, inode, map, path,
 						  flags, allocated);
 		if (IS_ERR(path))
@@ -3948,7 +3950,13 @@ ext4_ext_handle_unwritten_extents(handle_t *handle, struct inode *inode,
 			err = -EFSCORRUPTED;
 			goto errout;
 		}
-		map->m_flags |= EXT4_MAP_UNWRITTEN;
+		/* Don't mark unwritten if the extent has been zeroed out. */
+		path = ext4_find_extent(inode, map->m_lblk, path, flags);
+		if (IS_ERR(path))
+			return path;
+		depth = ext_depth(inode);
+		if (ext4_ext_is_unwritten(path[depth].p_ext))
+			map->m_flags |= EXT4_MAP_UNWRITTEN;
 		goto out;
 	}
 	/* IO end_io complete, convert the filled extent to written */
-- 
2.46.1