linux-ext4 - Re: [PATCH] ext4: Use optimized mballoc scanning regardless of inode format

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Message-ID: <4b18f416-28da-45d3-8887-48f804d9e84a@huawei.com>
Date: Fri, 9 Jan 2026 10:00:33 +0800
From: Baokun Li <libaokun1@...wei.com>
To: Jan Kara <jack@...e.cz>
CC: <linux-ext4@...r.kernel.org>, Ted Tso <tytso@....edu>,
	<libaokun9@...il.com>
Subject: Re: [PATCH] ext4: Use optimized mballoc scanning regardless of inode
 format

On 2026-01-09 00:09, Jan Kara wrote:
> Currently we don't used mballoc optimized scanning (using max free
> extent order and avg free extent order group lists) for inodes with
> indirect block based format. This is confusing for users and I don't see
> a good reason for that. Even with indirect block based inode format we
> can spend big amount of time searching for free blocks for large
> filesystems with fragmented free space. To add to the confusion before
> commit 077d0c2c78df ("ext4: make mb_optimize_scan performance mount
> option work with extents") optimized scanning was applied *only* to
> indirect block based inodes so that commit appears as a performance
> regression to some users. Just use optimized scanning whenever it is
> enabled by mount options.
>
> Signed-off-by: Jan Kara <jack@...e.cz>

Makes sense. Block allocation should not be tied to the inode format,
and we should remove this restriction.

However, inodes with the indirect block based format only support
32-bit physical block numbers. We already check the maximum supported
block group in ext4_mb_scan_groups_linear, but we don’t perform the
same check in ext4_mb_scan_groups_xa_range.

So if we want to drop this restriction, we need to specify the
appropriate end value for inodes using the indirect block based format
in ext4_mb_scan_groups_xa_range; otherwise, an overflow could occur and
lead to corrupted block allocation.


Regards,
Baokun

> ---
>  fs/ext4/mballoc.c | 2 --
>  1 file changed, 2 deletions(-)
>
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index 56d50fd3310b..4ee7ab4ce86e 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -1133,8 +1133,6 @@ static inline int should_optimize_scan(struct ext4_allocation_context *ac)
>  		return 0;
>  	if (ac->ac_criteria >= CR_GOAL_LEN_SLOW)
>  		return 0;
> -	if (!ext4_test_inode_flag(ac->ac_inode, EXT4_INODE_EXTENTS))
> -		return 0;
>  	return 1;
>  }
>