Current code will always truncate tailing page if its alloc_start is
smaller than inode size.

This behavior will cause a lot of unneeded COW page size extent.

This patch will avoid such problem.

Signed-off-by: Qu Wenruo <quwen...@cn.fujitsu.com>
---
v2:
  Newly introduced
---
 fs/btrfs/file.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index d638d34..ad30b37 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -2640,7 +2640,7 @@ static long btrfs_fallocate(struct file *file, int mode,
                                        alloc_start);
                if (ret)
                        goto out;
-       } else {
+       } else if (offset + len > inode->i_size) {
                /*
                 * If we are fallocating from the end of the file onward we
                 * need to zero out the end of the page if i_size lands in the
-- 
2.6.1

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