On 2025/6/28 3:14, Jan Kara wrote:

On Mon 23-06-25 15:32:57, Baokun Li wrote:

...

Groups with no free blocks shouldn't be in any average fragment size list. However, when all blocks in a group are allocated(i.e., bb_fragments or bb_free is 0), we currently skip updating the average fragment size, which means the group isn't removed from its previous s_mb_avg_fragment_size[old] list.

This created "zombie" groups that were always skipped during traversal as they couldn't satisfy any block allocation requests, negatively impacting traversal efficiency.

Therefore, when a group becomes completely free, bb_avg_fragment_size_order

			     ^^^ full

Oh, thank you for pointing out that typo! I'll correct it in the next version.

Thanks, Baokun

...

is now set to -1. If the old order was not -1, a removal operation is performed; if the new order is not -1, an insertion is performed.

Fixes: 196e402adf2e ("ext4: improve cr 0 / cr 1 group scanning") CC: stable@vger.kernel.org Signed-off-by: Baokun Li libaokun1@huawei.com

Good catch! The patch looks good. Feel free to add:

Reviewed-by: Jan Kara jack@suse.cz

						Honza

...

---

fs/ext4/mballoc.c | 36 ++++++++++++++++++------------------ 1 file changed, 18 insertions(+), 18 deletions(-)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c index 94950b07a577..e6d6c2da3c6e 100644 --- a/fs/ext4/mballoc.c +++ b/fs/ext4/mballoc.c @@ -841,30 +841,30 @@ static void mb_update_avg_fragment_size(struct super_block *sb, struct ext4_group_info *grp) { struct ext4_sb_info *sbi = EXT4_SB(sb);

• int new_order;

• int new, old;

• if (!test_opt2(sb, MB_OPTIMIZE_SCAN) || grp->bb_fragments == 0)

• if (!test_opt2(sb, MB_OPTIMIZE_SCAN)) return;

• new_order = mb_avg_fragment_size_order(sb,

• 			grp->bb_free / grp->bb_fragments);
  

• if (new_order == grp->bb_avg_fragment_size_order)

• old = grp->bb_avg_fragment_size_order;
• new = grp->bb_fragments == 0 ? -1 :

•      mb_avg_fragment_size_order(sb, grp->bb_free / grp->bb_fragments);
  

• if (new == old) return;

• if (grp->bb_avg_fragment_size_order != -1) {

• write_lock(&sbi->s_mb_avg_fragment_size_locks[
  

• 			grp->bb_avg_fragment_size_order]);
  

• if (old >= 0) {

• write_lock(&sbi->s_mb_avg_fragment_size_locks[old]);
  

  list_del(&grp->bb_avg_fragment_size_node);

• write_unlock(&sbi->s_mb_avg_fragment_size_locks[
  

• 			grp->bb_avg_fragment_size_order]);
  

• }
• grp->bb_avg_fragment_size_order = new_order;
• write_lock(&sbi->s_mb_avg_fragment_size_locks[

• 			grp->bb_avg_fragment_size_order]);
  

• list_add_tail(&grp->bb_avg_fragment_size_node,

• &sbi->s_mb_avg_fragment_size[grp->bb_avg_fragment_size_order]);
  

• write_unlock(&sbi->s_mb_avg_fragment_size_locks[

• 			grp->bb_avg_fragment_size_order]);
  

• write_unlock(&sbi->s_mb_avg_fragment_size_locks[old]);
  

• }
• grp->bb_avg_fragment_size_order = new;
• if (new >= 0) {

• write_lock(&sbi->s_mb_avg_fragment_size_locks[new]);
  

• list_add_tail(&grp->bb_avg_fragment_size_node,
  

• 		&sbi->s_mb_avg_fragment_size[new]);
  

• write_unlock(&sbi->s_mb_avg_fragment_size_locks[new]);
  

• } }

/* -- 2.46.1