linux-ext4 - [RFC PATCH v2 07/25] iomap: don't increase i

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Date: Tue,  2 Jan 2024 20:39:00 +0800
From: Zhang Yi <yi.zhang@...weicloud.com>
To: linux-ext4@...r.kernel.org
Cc: linux-fsdevel@...r.kernel.org,
	tytso@....edu,
	adilger.kernel@...ger.ca,
	jack@...e.cz,
	ritesh.list@...il.com,
	hch@...radead.org,
	djwong@...nel.org,
	willy@...radead.org,
	yi.zhang@...wei.com,
	yi.zhang@...weicloud.com,
	chengzhihao1@...wei.com,
	yukuai3@...wei.com,
	wangkefeng.wang@...wei.com
Subject: [RFC PATCH v2 07/25] iomap: don't increase i_size if it's not a write operation

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

Increase i_size in iomap_zero_range() looks not needed, the caller
should handle it. Especially, when truncate partial block, we should
not increase i_size beyond the new EOF here. It dosn't affect xfs and
gfs2 now because they reset the new file size after zero out, it doesn't
matter that a brief increase in i_size. But it will affect ext4 because
it set file size before truncate, so avoid increasing if it's not a
write path.

Signed-off-by: Zhang Yi <yi.zhang@...wei.com>
---
 fs/iomap/buffered-io.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index e0c9cede82ee..293ba00e4bc0 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -887,6 +887,7 @@ static size_t iomap_write_end(struct iomap_iter *iter, loff_t pos, size_t len,
 {
 	const struct iomap *srcmap = iomap_iter_srcmap(iter);
 	loff_t old_size = iter->inode->i_size;
+	bool update_size = iter->flags & IOMAP_WRITE;
 	size_t ret;
 
 	if (srcmap->type == IOMAP_INLINE) {
@@ -903,13 +904,13 @@ static size_t iomap_write_end(struct iomap_iter *iter, loff_t pos, size_t len,
 	 * cache.  It's up to the file system to write the updated size to disk,
 	 * preferably after I/O completion so that no stale data is exposed.
 	 */
-	if (pos + ret > old_size) {
+	if (update_size && pos + ret > old_size) {
 		i_size_write(iter->inode, pos + ret);
 		iter->iomap.flags |= IOMAP_F_SIZE_CHANGED;
 	}
 	__iomap_put_folio(iter, pos, ret, folio);
 
-	if (old_size < pos)
+	if (update_size && old_size < pos)
 		pagecache_isize_extended(iter->inode, old_size, pos);
 	if (ret < len)
 		iomap_write_failed(iter->inode, pos + ret, len - ret);
-- 
2.39.2