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Date: Wed, 20 Mar 2024 11:52:58 -0500
From: Frederick Lawler <fred@cloudflare.com>
To: Theodore Ts'o <tytso@mit.edu>
Cc: linux-ext4@vger.kernel.org, Ojaswin Mujoo <ojaswin@linux.ibm.com>,
	Ritesh Harjani <ritesh.list@gmail.com>,
	linux-kernel@vger.kernel.org, Jan Kara <jack@suse.cz>,
	glandvador@yahoo.com, bugzilla@eyal.emu.id.au,
	kernel-team@cloudflare.com
Subject: Re: [PATCH 0/1] Fix for recent bugzilla reports related to long
 halts during block allocation
Message-ID: <ZfsUaicHDpOtkkVv@CMGLRV3>
References: <cover.1702455010.git.ojaswin@linux.ibm.com>
 <170476879011.637731.13228432208887255974.b4-ty@mit.edu>
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In-Reply-To: <170476879011.637731.13228432208887255974.b4-ty@mit.edu>

Hi Theodore and Ojaswin,

On Mon, Jan 08, 2024 at 09:53:18PM -0500, Theodore Ts'o wrote:
> 
> On Fri, 15 Dec 2023 16:49:49 +0530, Ojaswin Mujoo wrote:
> > This patch intends to fix the recent bugzilla [1] report where the
> > kworker flush thread seemed to be taking 100% CPU utilizationa and was
> > slowing down the whole system. The backtrace indicated that we were
> > stuck in mballoc allocation path. The issue was only seen kernel 6.5+
> > and when ext4 was mounted with -o stripe (or stripe option was
> > implicitly added due us mkfs flags used).
> > 
> > [...]
> 
> Applied, thanks!

I backported this patch to at least 6.6 and tested on our fleet of
software RAID 0 NVME SSD nodes. This change worked very nicely
for us. We're interested in backporting this to at least 6.6.

I tried looking at xfstests, and didn't really see a good match
(user error?) to validate the fix via that. So I'm a little unclear what
the path forward here is.

Although we experienced this issue in 6.1, I didn't backport to 6.1 and
test to verify this also works there, however, setting stripe to 0 did in
the 6.1 case.

Best,
Fred

> 
> [1/1] ext4: fallback to complex scan if aligned scan doesn't work
>       commit: a26b6faf7f1c9c1ba6edb3fea9d1390201f2ed50
> 
> Best regards,
> -- 
> Theodore Ts'o <tytso@mit.edu>