linux-kernel - Re: [PATCH 0/5] selftests/mm: Implement support for arm64 on va

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Date:   Thu, 23 Mar 2023 14:14:36 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Chaitanya S Prakash <chaitanyas.prakash@....com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Shuah Khan <shuah@...nel.org>, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH 0/5] selftests/mm: Implement support for arm64 on va

On Thu, Mar 23, 2023 at 04:22:38PM +0530, Chaitanya S Prakash wrote:
> The va_128TBswitch selftest is designed and implemented for PowerPC and
> x86 architectures which support a 128TB switch, up to 256TB of virtual
> address space and hugepage sizes of 16MB and 2MB respectively. Arm64
> platforms on the other hand support a 256Tb switch, up to 4PB of virtual
> address space and a default hugepage size of 512MB when 64k pagesize is
> enabled.
> 
> These architectural differences require introducing support for arm64
> platforms, after which a more generic naming convention is suggested.
> The in code comments are amended to provide a more platform independent
> explanation of the working of the code and nr_hugepages are configured
> as required. Finally, the file running the testcase is modified in order
> to prevent skipping of hugetlb testcases of va_high_addr_switch.
> 
> This series has been tested on 6.3.0-rc3 kernel, both on arm64 and x86
> platforms.
> 
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Aneesh Kumar K.V <aneesh.kumar@...ux.ibm.com>
> Cc: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Cc: Shuah Khan <shuah@...nel.org>
> Cc: linux-mm@...ck.org
> Cc: linux-kselftest@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org 
> 
> Chaitanya S Prakash (5):
>   selftests/mm: Add support for arm64 platform on va switch
>   selftests/mm: Rename va_128TBswitch to va_high_addr_switch
>   selftests/mm: Add platform independent in code comments
>   selftests/mm: Configure nr_hugepages for arm64
>   selftests/mm: Run hugetlb testcases of va switch
> 
>  tools/testing/selftests/mm/Makefile           |  4 +-
>  tools/testing/selftests/mm/run_vmtests.sh     | 12 +++++-
>  ...va_128TBswitch.c => va_high_addr_switch.c} | 41 +++++++++++++++----
>  ..._128TBswitch.sh => va_high_addr_switch.sh} |  6 ++-
>  4 files changed, 49 insertions(+), 14 deletions(-)
>  rename tools/testing/selftests/mm/{va_128TBswitch.c => va_high_addr_switch.c} (86%)
>  rename tools/testing/selftests/mm/{va_128TBswitch.sh => va_high_addr_switch.sh} (89%)

The patchset looks sane to me, but I have question: why arm64 has switch
on 256TB. The reason we have the switch is to keep system backward
compatible.

Maybe it is better to make arm64 switch also on 128TB to make it
compatible across architectures?

-- 
  Kiryl Shutsemau / Kirill A. Shutemov