Re: [Regression] ext4: changes to mb_optimize_scan cause issues on Raspberry Pi

From: Stefan Wahren <stefan.wahren@i2se.com>
To: Jan Kara <jack@suse.cz>
Cc: linux-ext4@vger.kernel.org, Ojaswin Mujoo <ojaswin@linux.ibm.com>,
	Harshad Shirwadkar <harshadshirwadkar@gmail.com>,
	Theodore Ts'o <tytso@mit.edu>,
	Ritesh Harjani <riteshh@linux.ibm.com>,
	linux-fsdevel@vger.kernel.org,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Geetika.Moolchandani1@ibm.com, regressions@lists.linux.dev
Subject: Re: [Regression] ext4: changes to mb_optimize_scan cause issues on Raspberry Pi
Date: Fri, 29 Jul 2022 07:30:25 +0200	[thread overview]
Message-ID: <2217188c-7009-f142-3e7e-b3e61d2c1324@i2se.com> (raw)
In-Reply-To: <20220728100055.efbvaudwp3ofolpi@quack3>

Hi Jan,

Am 28.07.22 um 12:00 schrieb Jan Kara:
> Hello!
> Can you run "iostat -x 1" while the download is running so that we can see
> roughly how the IO pattern looks?
>
> Also can get filesystem metadata image of your card like:
>    e2image -r <fs-device> - | gzip >/tmp/ext4-image.gz
>
> and put it somewhere for download? The image will contain only fs metadata,
> not data so it should be relatively small and we won't have access to your
> secrets ;). With the image we'd be able to see how the free space looks
> like and whether it perhaps does not trigger some pathological behavior.
>
> My current suspicion is that because the new allocator strategy spreads
> allocations over more block groups, we end up with more open erase blocks
> on the SD card which forces the firmware to do more garbage collection and
> RMW of erase blocks and write performance tanks...
>
> Thanks.
thanks for your feedback. Unfortunately i'm busy the next days, so it 
will take some time to provide this.
> 								Honza
>