linux-kernel - Re: [PATCH 1/3] selftests/zram: Remove obsolete max_comp

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Date:   Wed, 26 Jan 2022 10:35:32 -0700
From:   Shuah Khan <skhan@...uxfoundation.org>
To:     Petr Vorel <pvorel@...e.cz>,
        "xuyang2018.jy@...itsu.com" <xuyang2018.jy@...itsu.com>
Cc:     "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
        "shuah@...nel.org" <shuah@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "naresh.kamboju@...aro.org" <naresh.kamboju@...aro.org>,
        "aleksei.kodanev@...l-sw.com" <aleksei.kodanev@...l-sw.com>,
        Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH 1/3] selftests/zram: Remove obsolete max_comp_streams
 interface

On 1/26/22 12:13 AM, Petr Vorel wrote:
> Hi all,
> 
>> on 2022/1/26 4:33, Shuah Khan wrote :
>>> On 12/15/21 2:56 AM, Yang Xu wrote:
>>>> Since kernel commit 43209ea2d17a ("zram: remove max_comp_streams
>>>> internals"), zram has
>>>> switched to per-cpu streams. Even kernel still keep this interface for
>>>> some reasons, but
>>>> writing to max_comp_stream doesn't take any effect. So remove it.
> 
>>> I get that max_comp_stream doesn't do anything since this referenced
>>> commit. Don't we need this test on older kernels since older kernels
>>> still support max_comp_stream?
> 
>> I read the following info from kernel selftest documentation
>> https://www.kernel.org/doc/html/latest/dev-tools/kselftest.html
> 
>> "The kernel contains a set of “self tests” under the
>> tools/testing/selftests/ directory. These are intended to be small tests
>> to exercise individual code paths in the kernel. Tests are intended to
>> be run after building, installing and booting a kernel."
> 
>> So, we can build older kernel(use older kernel source) if we want to
>> test older kernel.
> 
>> IMO, kernel selftest is different from other testsuit(ie ltp, this
>> shuould think about api changes because ltp may test on different kernel).
> Yes, that's how I understand the difference with approach of in kselftest - the
> kernel tree testsuite and LTP - the out-of-tree testsuite.
> 

Removing max_comp_stream test appears to be motivated by the fact it isn't
needed on newer kernels.

Kselftest from mainline can be run on older stable kernels. This is a use-case
for a lot test rings. The idea is that when a new test gets added for older
code to regression test a bug, we should be able to run that test on an older
kernel. This is the reason why we don't remove code that can still test an older
kernel and make sure it skips gracefully.

Hence, I won't be taking this patch.

thanks,
-- Shuah