linux-kernel - Re: [RESEND PATCH v7 09/10] selftests/mm/cow: Generalize do_run_with

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Date:   Mon, 27 Nov 2023 15:17:09 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Ryan Roberts <ryan.roberts@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>,
        Yin Fengwei <fengwei.yin@...el.com>,
        Yu Zhao <yuzhao@...gle.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Yang Shi <shy828301@...il.com>,
        "Huang, Ying" <ying.huang@...el.com>, Zi Yan <ziy@...dia.com>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Itaru Kitayama <itaru.kitayama@...il.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        John Hubbard <jhubbard@...dia.com>,
        David Rientjes <rientjes@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Hugh Dickins <hughd@...gle.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>
Cc:     linux-mm@...ck.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RESEND PATCH v7 09/10] selftests/mm/cow: Generalize
 do_run_with_thp() helper

On 27.11.23 15:11, Ryan Roberts wrote:
> On 27/11/2023 13:59, David Hildenbrand wrote:
>>>>
>>>>> +    pmdsize = read_pmd_pagesize();
>>>>> +    if (pmdsize)
>>>>> +        ksft_print_msg("[INFO] detected PMD-mapped THP size: %zu KiB\n",
>>>>
>>>> Maybe simply: "detected PMD size". Zes, we read it via the THP interface, but
>>>> that shouldn't matter much.
>>>
>>> Err, just want to clarify what you are suggesting. With the current patch you
>>> will see something like:
>>
>> Not with this patch, but with the other ones, yes :)
> 
> Yep, we are on the same page (folio)...
> 
>>
>>>
>>> [INFO] detected PMD-mapped THP size: 2048 KiB
>>> [INFO] detected small-sized THP size: 64 KiB
>>> [INFO] detected small-sized THP size: 128 KiB
>>> ...
>>> [INFO] detected small-sized THP size: 1024 KiB
>>>
>>>
>>> Are you suggesting something like this:
>>>
>>> [INFO] detected PMD size: 2048 KiB
>>> [INFO] detected THP size: 64 KiB
>>> [INFO] detected THP size: 128 KiB
>>> ...
>>> [INFO] detected THP size: 2048 KiB
>>>
>>
>> Yes. If you'd detect that 2M is actually disabled, you could still log the PMD
>> size only.
> 
> Note that in the final patch, where I test the other THP sizes, I'm not
> detecting which sizes the sysadmin has enabled, I'm detecting the set of sizes
> that can be enabled, then explicitly enabling the size (exclusively) when I test
> it. So there is no chance of reading PMD size but not having 2M THP. Minor point
> though.

Ah, makes sense, I missed that and thought we'd check if that size is 
actually possible.

-- 
Cheers,

David / dhildenb