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

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Message-ID: <v2qznr26v5tbgscpnty3hujsmz3e2ajf6iuskdjdbk5yfyaxjf@lbd5yiju4r6s>
Date: Fri, 9 Jan 2026 11:03:46 +0100
From: Jan Kara <jack@...e.cz>
To: Baokun Li <libaokun1@...wei.com>
Cc: Jan Kara <jack@...e.cz>, 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 Fri 09-01-26 10:00:33, Baokun Li wrote:
> 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.

Good point. I'll fix that up and send v2. Thanks for review!

								Honza

> 
> 
> 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;
> >  }
> >  
> 
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR