Re: [PATCH 1/3] selftests/zram: Remove obsolete max_comp_streams interface

[Shuah Khan]

On 1/26/22 11:24 AM, Petr Vorel wrote:
> > 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.
>
> Thanks for clarifying this approach. It might be worth of documenting it in
> dev-tools/kselftest.rst.

I will send out a patch clarifying this.

thanks,
-- Shuah