linux-kernel - Re: ext4 writeback performance issue in 6.12

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Message-Id: <20251009102259.529708-1-matt@readmodwrite.com>
Date: Thu,  9 Oct 2025 11:22:59 +0100
From: Matt Fleming <matt@...dmodwrite.com>
To: Theodore Ts'o <tytso@....edu>
Cc: adilger.kernel@...ger.ca,
	jack@...e.cz,
	kernel-team@...udflare.com,
	libaokun1@...wei.com,
	linux-ext4@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	willy@...radead.org
Subject: Re: ext4 writeback performance issue in 6.12

On Wed, Oct 08, 2025 at 12:26:55PM -0400, Theodore Ts'o wrote:
> On Wed, Oct 08, 2025 at 04:07:05PM +0100, Matt Fleming wrote:
> > > 
> > > These machines are striped and are using noatime:
> > > 
> > > $ grep ext4 /proc/mounts
> > > /dev/md127 /state ext4 rw,noatime,stripe=1280 0 0
> > > 
> > > Is there some tunable or configuration option that I'm missing that
> > > could help here to avoid wasting time in
> > > ext4_mb_find_good_group_avg_frag_lists() when it's most likely going to
> > > fail an order 9 allocation anyway?
> 
> Can you try disabling stripe parameter?  If you are willing to try the
> latest mainline kernel, there are some changes that *might* make a
> different, but RAID stripe alignment has been causing problems.

Thanks Ted. I'm going to try disabling the stripe parameter now. I'll report
back shortly.