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Date:   Mon, 27 Nov 2023 14:11:52 +0000
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Subject: Re: [RESEND PATCH v7 09/10] selftests/mm/cow: Generalize
 do_run_with_thp() helper
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To:     David Hildenbrand <david@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Matthew Wilcox <willy@infradead.org>,
        Yin Fengwei <fengwei.yin@intel.com>,
        Yu Zhao <yuzhao@google.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Anshuman Khandual <anshuman.khandual@arm.com>,
        Yang Shi <shy828301@gmail.com>,
        "Huang, Ying" <ying.huang@intel.com>, Zi Yan <ziy@nvidia.com>,
        Luis Chamberlain <mcgrof@kernel.org>,
        Itaru Kitayama <itaru.kitayama@gmail.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        John Hubbard <jhubbard@nvidia.com>,
        David Rientjes <rientjes@google.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Hugh Dickins <hughd@google.com>,
        Kefeng Wang <wangkefeng.wang@huawei.com>
Cc:     linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org,
        linux-kernel@vger.kernel.org
References: <20231122162950.3854897-1-ryan.roberts@arm.com>
 <20231122162950.3854897-10-ryan.roberts@arm.com>
 <ead82cbe-19c9-43ce-9f28-7ced118b130a@redhat.com>
 <15c288aa-feab-4d3a-af33-b87481eaffe3@arm.com>
 <1ebb9a53-63ee-430c-ba65-8e48eff6d25c@redhat.com>
From:   Ryan Roberts <ryan.roberts@arm.com>
In-Reply-To: <1ebb9a53-63ee-430c-ba65-8e48eff6d25c@redhat.com>
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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.

> 
> So for this patch only as a preparation
> 
> [INFO] detected PMD size: 2048 KiB
> [INFO] detected THP size: 2048 KiB
> 
> Just a thought.

Yep this is exactly how I've just reworked it.