Re: [PATCH] f2fs: skip f2fs_preallocate_blocks() for overwrite case

From: Chao Yu
Date: Tue Sep 28 2021 - 20:05:16 EST

On 2021/9/29 3:08, Jaegeuk Kim wrote:
On 09/28, Chao Yu wrote:
In f2fs_file_write_iter(), let's use f2fs_overwrite_io() to
check whethere it is overwrite case, for such case, we can skip
f2fs_preallocate_blocks() in order to avoid f2fs_do_map_lock(),
which may be blocked by checkpoint() potentially.

Signed-off-by: Chao Yu <chao@xxxxxxxxxx>
fs/f2fs/file.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index 13deae03df06..51fecb2f4db5 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -4321,6 +4321,10 @@ static ssize_t f2fs_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
preallocated = true;
target_size = iocb->ki_pos + iov_iter_count(from);
+ if (f2fs_overwrite_io(inode, iocb->ki_pos,
+ iov_iter_count(from)))
+ goto write;

This calls f2fs_map_blocks() which can be duplicate, if it's not the overwirte
case. Do we have other benefit?

f2fs_overwrite_io() will break for append write case w/ below check:

if (pos + len > i_size_read(inode))
return false;

I guess we may only suffer double f2fs_map_blocks() for write hole
case, e.g. truncate to large size & write inside the filesize. For
this case, how about adding a condition to allow double f2fs_map_blocks()
only if write size is smaller than a threshold?


err = f2fs_preallocate_blocks(iocb, from);
if (err) {