linux-kernel - Re: [PATCH v2 04/16] ext4: utilize multiple global goals to reduce contention

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Message-ID: <trjf7lqckchx6bc3p4lwh5yy3bqczo6yvdll7ujguhvvezwtja@cpfhj6ai7gzp>
Date: Mon, 30 Jun 2025 19:41:41 +0200
From: Jan Kara <jack@...e.cz>
To: Baokun Li <libaokun1@...wei.com>
Cc: Jan Kara <jack@...e.cz>, linux-ext4@...r.kernel.org, tytso@....edu, 
	adilger.kernel@...ger.ca, ojaswin@...ux.ibm.com, linux-kernel@...r.kernel.org, 
	yi.zhang@...wei.com, yangerkun@...wei.com
Subject: Re: [PATCH v2 04/16] ext4: utilize multiple global goals to reduce
 contention

On Mon 30-06-25 18:02:49, Baokun Li wrote:
> On 2025/6/30 16:38, Jan Kara wrote:
> > We could make streaming goal to be ext4_fsblk_t so that also offset of the
> > last big allocation in the group is recorded as I wrote above. That would
> > tend to pack big allocations in each group together which is benefitial to
> > combat fragmentation even with higher proportion of groups that are streaming
> > goals (and likely becomes more important as the blocksize and thus group
> > size grow). We can discuss proper number of slots for streaming allocation
> > (I'm not hung up on it being quarter of the group count) but I'm convinced
> > sb->s_groups_count is too much :)
> > 
> > 								Honza
> 
> I think sbi->s_groups_count / 4 is indeed acceptable. However, I don't
> believe recording offsets is necessary. As groups become larger,
> contention for groups will intensify, and adding offsets would only
> make this contention worse.

I agree the contention for groups will increase when the group count goes
down. I just thought offsets may help to find free space faster in large
groups (and thus reduce contention) and also reduce free space
fragmentation within a group (by having higher chances of placing large
allocations close together within a group) but maybe that's not the case.
Offsets are definitely not requirement at this point.

								Honza

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