From: Qu Wenruo <wqu@xxxxxxxx>
commit 484167da77739a8d0e225008c48e697fd3f781ae upstream.
[BUG]
There are users using autodefrag mount option reporting obvious increase
in IO:
> If I compare the write average (in total, I don't have it per process)
> when taking idle periods on the same machine:
> Linux 5.16:
> without autodefrag: ~ 10KiB/s
> with autodefrag: between 1 and 2MiB/s.
>
> Linux 5.15:
> with autodefrag:~ 10KiB/s (around the same as without
> autodefrag on 5.16)
[CAUSE]
When autodefrag mount option is enabled, btrfs_defrag_file() will be
called with @max_sectors = BTRFS_DEFRAG_BATCH (1024) to limit how many
sectors we can defrag in one try.
And then use the number of sectors defragged to determine if we need to
re-defrag.
But commit b18c3ab2343d ("btrfs: defrag: introduce helper to defrag one
cluster") uses wrong unit to increase @sectors_defragged, which should
be in unit of sector, not byte.
This means, if we have defragged any sector, then @sectors_defragged
will be >= sectorsize (normally 4096), which is larger than
BTRFS_DEFRAG_BATCH.
This makes the @max_sectors check in defrag_one_cluster() to underflow,
rendering the whole @max_sectors check useless.
Thus causing way more IO for autodefrag mount options, as now there is
no limit on how many sectors can really be defragged.
[FIX]
Fix the problems by:
- Use sector as unit when increasing @sectors_defragged
- Include @sectors_defragged > @max_sectors case to break the loop
- Add extra comment on the return value of btrfs_defrag_file()
Reported-by: Anthony Ruhier <aruhier@xxxxxxxxxxx>
Fixes: b18c3ab2343d ("btrfs: defrag: introduce helper to defrag one cluster")
Link: https://lore.kernel.org/linux-btrfs/0a269612-e43f-da22-c5bc-b34b1b56ebe8@xxxxxxxxxxx/
CC: stable@xxxxxxxxxxxxxxx # 5.16
Reviewed-by: Filipe Manana <fdmanana@xxxxxxxx>
Signed-off-by: Qu Wenruo <wqu@xxxxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/btrfs/ioctl.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -1416,8 +1416,8 @@ static int defrag_one_cluster(struct btr
list_for_each_entry(entry, &target_list, list) {
u32 range_len = entry->len;
- /* Reached the limit */
- if (max_sectors && max_sectors == *sectors_defragged)
+ /* Reached or beyond the limit */
+ if (max_sectors && *sectors_defragged >= max_sectors)
break;
if (max_sectors)
@@ -1439,7 +1439,8 @@ static int defrag_one_cluster(struct btr
extent_thresh, newer_than, do_compress);
if (ret < 0)
break;
- *sectors_defragged += range_len;
+ *sectors_defragged += range_len >>
+ inode->root->fs_info->sectorsize_bits;
}
out:
list_for_each_entry_safe(entry, tmp, &target_list, list) {
@@ -1458,6 +1459,9 @@ out:
* @newer_than: minimum transid to defrag
* @max_to_defrag: max number of sectors to be defragged, if 0, the whole inode
* will be defragged.
+ *
+ * Return <0 for error.
+ * Return >=0 for the number of sectors defragged.
*/
int btrfs_defrag_file(struct inode *inode, struct file_ra_state *ra,
struct btrfs_ioctl_defrag_range_args *range,
