linux-ext4 - Re: [Regression] ext4: changes to mb_optimize

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Date:   Fri, 29 Jul 2022 07:30:25 +0200
From:   Stefan Wahren <stefan.wahren@...e.com>
To:     Jan Kara <jack@...e.cz>
Cc:     linux-ext4@...r.kernel.org, Ojaswin Mujoo <ojaswin@...ux.ibm.com>,
        Harshad Shirwadkar <harshadshirwadkar@...il.com>,
        Theodore Ts'o <tytso@....edu>,
        Ritesh Harjani <riteshh@...ux.ibm.com>,
        linux-fsdevel@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Geetika.Moolchandani1@....com, regressions@...ts.linux.dev
Subject: Re: [Regression] ext4: changes to mb_optimize_scan cause issues on
 Raspberry Pi

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
>