linux-kernel - Re: [PATCH 1/3] selftests/mm: make file-backed THP split work by setting force option

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Message-ID: <d66cea11-9522-43f4-8590-2e11ed43a8e5@redhat.com>
Date: Wed, 22 Jan 2025 16:27:35 +0100
From: David Hildenbrand <david@...hat.com>
To: Zi Yan <ziy@...dia.com>, linux-mm@...ck.org,
 Andrew Morton <akpm@...ux-foundation.org>,
 Baolin Wang <baolin.wang@...ux.alibaba.com>
Cc: "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
 "Matthew Wilcox (Oracle)" <willy@...radead.org>,
 Ryan Roberts <ryan.roberts@....com>, Hugh Dickins <hughd@...gle.com>,
 Yang Shi <yang@...amperecomputing.com>, Miaohe Lin <linmiaohe@...wei.com>,
 Kefeng Wang <wangkefeng.wang@...wei.com>, Yu Zhao <yuzhao@...gle.com>,
 John Hubbard <jhubbard@...dia.com>, linux-kselftest@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] selftests/mm: make file-backed THP split work by
 setting force option

On 22.01.25 16:16, Zi Yan wrote:
> On Wed Jan 22, 2025 at 9:26 AM EST, David Hildenbrand wrote:
>> On 22.01.25 13:40, Zi Yan wrote:
>>> Commit acd7ccb284b8 ("mm: shmem: add large folio support for tmpfs")
>>> changes huge=always to allocate THP/mTHP based on write size and
>>> split_huge_page_test does not write PMD size data, so file-back THP is not
>>> created during the test.
>>
>> Just curious, why can't we write PMD size data instead, to avoid messing
>> with the "force" option?
> 
> It also works. I used "force", because I notice that it is intended for
> testing. Using it might be more future proof, in case huge=always changes
> its semantics again in the future.

I recall discussing with Hugh in an upstream call that "force" is a 
relict from older times, so naturally I would have just adjusted the 
test case to trigger the PMD scenario. No strong opinion, though, was 
just wondering.

-- 
Cheers,

David / dhildenb