Re: [PATCH 0/1] Possible bug in zram on ppc64le on vfat

From: Petr Vorel <pvorel@suse.cz>
To: Minchan Kim <minchan@kernel.org>
Cc: ltp@lists.linux.it, linux-block@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org,
	Nitin Gupta <ngupta@vflare.org>,
	Sergey Senozhatsky <senozhatsky@chromium.org>,
	Jens Axboe <axboe@kernel.dk>,
	OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>,
	Martin Doucha <mdoucha@suse.cz>,
	Yang Xu <xuyang2018.jy@fujitsu.com>
Subject: Re: [PATCH 0/1] Possible bug in zram on ppc64le on vfat
Date: Fri, 11 Nov 2022 10:29:28 +0100	[thread overview]
Message-ID: <Y24V+AUuivt1F/Kw@pevik> (raw)
In-Reply-To: <Y22DiF5Q5EDUIrZE@google.com>

> On Mon, Nov 07, 2022 at 10:47:33PM +0100, Petr Vorel wrote:
> > Hi Minchan,

> > > On Mon, Nov 07, 2022 at 08:11:35PM +0100, Petr Vorel wrote:
> > > > Hi all,

> > > > following bug is trying to workaround an error on ppc64le, where
> > > > zram01.sh LTP test (there is also kernel selftest
> > > > tools/testing/selftests/zram/zram01.sh, but LTP test got further
> > > > updates) has often mem_used_total 0 although zram is already filled.

> > > Hi, Petr,

> > > Is it happening on only ppc64le?
> > I haven't seen it on other archs (x86_64, aarch64).

> > > Is it a new regression? What kernel version did you use?
> > Found on openSUSE kernel, which uses stable kernel releases 6.0.x.
> > It's probably much older, first I've seen it some years ago (I'm not able to find kernel version), but it was random. Now it's much more common.

> > Test runs on VM (I can give qemu command or whatever you need to know about it)
> > I'll try to verify it on some bare metal ppc64le.

> Hi Petr and Martin,

> Thanks for testing and meaning information.

> Could you tell how I could create VM to run ppc64le and run the test?
> I'd like to reproduce in my local to debug it.
I suppose you don't have ppc64le bare metal machine, thus you run on x86_64.

One way would be to install on host qemu-system-ppc64, download iso image of any
distro which supports ppc64le and install it with virt-manager (which would fill
necessary qemu params).

Other way, which I often use is to compile system with Buildroot distribution.
You can clone my Buildroot distro fork, branch debug/zram [1].
I put there in 3 commits my configuration.
I added 0001-zram-Debug-mm_stat_show.patch [2] on the top of 6.0.7 with little debugging.

What is now only needed is to 1) install on host qemu-system-ppc64
(speedup build + Buildroot is configured not to compile qemu-system-ppc64),
then:
$ make # takes time
$ ./output/images/start-qemu.sh serial-only

When I have ppc64le host with enough space, I often use rapido [3],
but that crashed stable kernel (another story which I'll report soon).

Hope that helps.

Kind regards,
Petr

[1] https://github.com/pevik/buildroot/commits/debug/zram
[2] https://github.com/pevik/buildroot/blob/debug/zram/0001-zram-Debug-mm_stat_show.patch
[3] https://github.com/rapido-linux/rapido