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Message-ID: <Y3zlrBQ8fgJyNm7G@pevik>
Date: Tue, 22 Nov 2022 16:07:24 +0100
From: Petr Vorel <pvorel@...e.cz>
To: Martin Doucha <mdoucha@...e.cz>
Cc: Sergey Senozhatsky <senozhatsky@...omium.org>,
Minchan Kim <minchan@...nel.org>, ltp@...ts.linux.it,
linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-kselftest@...r.kernel.org, Nitin Gupta <ngupta@...are.org>,
Jens Axboe <axboe@...nel.dk>,
OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
Yang Xu <xuyang2018.jy@...itsu.com>
Subject: Re: [PATCH 0/1] Possible bug in zram on ppc64le on vfat
> On 11. 11. 22 1:48, Sergey Senozhatsky wrote:
> > On (22/11/10 15:29), Martin Doucha wrote:
> > > I've tried to debug the issue and collected some interesting data (all
> > > values come from zram device with 25M size limit and zstd compression
> > > algorithm):
> > > - mm_stat values are correct after mkfs.vfat:
> > > 65536 220 65536 26214400 65536 0 0 0
> > > - mm_stat values stay correct after mount:
> > > 65536 220 65536 26214400 65536 0 0 0
> > > - the bug is triggered by filling the filesystem to capacity (using dd):
> > > 4194304 0 0 26214400 327680 64 0 0
> > Can you try using /dev/urandom for dd, not /dev/zero?
> > Do you still see zeroes in sysfs output or some random values?
> After 50 test runs on a kernel where the issue is confirmed, I could not
> reproduce the failure while filling the device from /dev/urandom instead of
> /dev/zero. The test reported compression ratio around 1.8-2.5 which means
> the memory usage reported by mm_stat was 10-13MB.
Martin, thanks a lot for reruning tests. I wonder problems on /dev/zero is a
kernel bug or just problem which should be workarounded.
> Note that I had to disable the other filesystems in the test because some of
> them kept failing with compression ratio <1.
Yes, I noted that as well at least on exfat and btrfs (if I remember correctly).
It wouldn't be a problem to just use it for vfat if we agreed test should be
modified.
Kind regards,
Petr
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