linux-kernel - Re: [PATCH] selftests/mm: Introduce a test program to assess swap entry allocation for thp

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Date: Fri, 21 Jun 2024 08:25:13 +0100
From: Ryan Roberts <ryan.roberts@....com>
To: David Hildenbrand <david@...hat.com>, Barry Song <21cnbao@...il.com>,
 akpm@...ux-foundation.org, shuah@...nel.org, linux-mm@...ck.org
Cc: chrisl@...nel.org, hughd@...gle.com, kaleshsingh@...gle.com,
 kasong@...cent.com, linux-kernel@...r.kernel.org, ying.huang@...el.com,
 linux-kselftest@...r.kernel.org, Barry Song <v-songbaohua@...o.com>
Subject: Re: [PATCH] selftests/mm: Introduce a test program to assess swap
 entry allocation for thp_swapout

On 20/06/2024 12:34, David Hildenbrand wrote:
> On 20.06.24 11:04, Ryan Roberts wrote:
>> On 20/06/2024 01:26, Barry Song wrote:
>>> From: Barry Song <v-songbaohua@...o.com>
>>>
>>> Both Ryan and Chris have been utilizing the small test program to aid
>>> in debugging and identifying issues with swap entry allocation. While
>>> a real or intricate workload might be more suitable for assessing the
>>> correctness and effectiveness of the swap allocation policy, a small
>>> test program presents a simpler means of understanding the problem and
>>> initially verifying the improvements being made.
>>>
>>> Let's endeavor to integrate it into the self-test suite. Although it
>>> presently only accommodates 64KB and 4KB, I'm optimistic that we can
>>> expand its capabilities to support multiple sizes and simulate more
>>> complex systems in the future as required.
>>
>> I'll try to summarize the thread with Huang Ying by suggesting this test program
>> is "neccessary but not sufficient" to exhaustively test the mTHP swap-out path.
>> I've certainly found it useful and think it would be a valuable addition to the
>> tree.
>>
>> That said, I'm not convinced it is a selftest; IMO a selftest should provide a
>> clear pass/fail result against some criteria and must be able to be run
>> automatically by (e.g.) a CI system.
> 
> Likely we should then consider moving other such performance-related thingies
> out of the selftests?

Yes, that would get my vote. But of the 4 tests you mentioned that use
clock_gettime(), it looks like transhuge-stress is the only one that doesn't
have a pass/fail result, so is probably the only candidate for moving.

The others either use the times as a timeout and determines failure if the
action didn't occur within the timeout (e.g. ksm_tests.c) or use it to add some
supplemental performance information to an otherwise functionality-oriented test.