Commit 1c320d8e authored by Baokun Li's avatar Baokun Li Committed by Theodore Ts'o
Browse files

ext4: fix zombie groups in average fragment size lists 



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 full, bb_avg_fragment_size_order
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: 196e402a ("ext4: improve cr 0 / cr 1 group scanning")
CC: stable@vger.kernel.org
Signed-off-by: default avatarBaokun Li <libaokun1@huawei.com>
Reviewed-by: default avatarJan Kara <jack@suse.cz>
Reviewed-by: default avatarZhang Yi <yi.zhang@huawei.com>
Link: https://patch.msgid.link/20250714130327.1830534-11-libaokun1@huawei.com


Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
parent e7f101a8

fs/ext4/mballoc.c

+18 −18
Original line number Diff line number Diff line
@@ -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]);

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

	}

	grp->bb_avg_fragment_size_order = new_order;

	write_lock(&sbi->s_mb_avg_fragment_size_locks[

					grp->bb_avg_fragment_size_order]);



	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[grp->bb_avg_fragment_size_order]);

	write_unlock(&sbi->s_mb_avg_fragment_size_locks[

					grp->bb_avg_fragment_size_order]);

				&sbi->s_mb_avg_fragment_size[new]);

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

	}

}



/*