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

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Message-Id: <D78PT6GILTYB.2QVXGSIG7YO9Y@nvidia.com>
Date: Wed, 22 Jan 2025 10:42:33 -0500
From: "Zi Yan" <ziy@...dia.com>
To: "David Hildenbrand" <david@...hat.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 Wed Jan 22, 2025 at 10:27 AM EST, David Hildenbrand wrote:
> 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.

Got it. Let me change it and resend. Thank you for the feedback.

-- 
Best Regards,
Yan, Zi