linux-kernel - Re: [PATCH v2] selftest: Add test for Soft-Dirty PTE bit

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Message-ID: <87lf553z5g.fsf@collabora.com>
Date:   Fri, 13 Aug 2021 15:47:23 -0400
From:   Gabriel Krisman Bertazi <krisman@...labora.com>
To:     Will Deacon <will@...nel.org>
Cc:     shuah@...nel.org, linux-kernel@...r.kernel.org,
        peterz@...radead.org, luto@...nel.org,
        linux-kselftest@...r.kernel.org, kernel@...labora.com
Subject: Re: [PATCH v2] selftest: Add test for Soft-Dirty PTE bit

Will Deacon <will@...nel.org> writes:

> On Thu, Jun 03, 2021 at 11:15:18AM -0400, Gabriel Krisman Bertazi wrote:
>> This introduces three tests:
>> 
>> 1) Sanity check soft dirty basic semantics: allocate area, clean, dirty,
>> check if the SD bit flipped.
>> 
>> 2) Check VMA reuse: validate the VM_SOFTDIRTY usage
>> 
>> 3) Check soft-dirty on huge pages
>> 
>> This was motivated by Will Deacon's fix commit 912efa17e512 ("mm: proc:
>> Invalidate TLB after clearing soft-dirty page state"). I was tracking the
>> same issue that he fixed, and this test would have caught it.
>> 
>> Cc: Will Deacon <will@...nel.org>
>> Signed-off-by: Gabriel Krisman Bertazi <krisman@...labora.com>
>> 
>> --
>> Changes since V1:
>>   - Fix last minute build break with page_size
>> ---
>>  tools/testing/selftests/Makefile              |   1 +
>>  tools/testing/selftests/soft-dirty/.gitignore |   1 +
>>  tools/testing/selftests/soft-dirty/Makefile   |   9 +
>>  .../testing/selftests/soft-dirty/soft-dirty.c | 254 ++++++++++++++++++
>>  4 files changed, 265 insertions(+)
>>  create mode 100644 tools/testing/selftests/soft-dirty/.gitignore
>>  create mode 100644 tools/testing/selftests/soft-dirty/Makefile
>>  create mode 100644 tools/testing/selftests/soft-dirty/soft-dirty.c
>
> Although I think adding a test for this is great (and I certainly wouldn't
> want to get in the way of that; quite the opposite), I notice that we
> already have test_softdirty() in selftests/vm/madv_populate.c. Would we be
> better off extending that test instead of introducing another one?

Hi, Will. Thanks for the review.

Looks like selftests/vm/madv_populate.c was merged after I sent this,
which explains why I missed it.  From a quick look, it also doesn't
verify the corner case of I'm checking here.  I will look into merging
the two tests, or at least moving this to vm/ and remove the overlap.

Thanks,

-- 
Gabriel Krisman Bertazi