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Message-ID: <974467f0-de25-40d4-8a8b-1c7e0b91e719@redhat.com>
Date:   Mon, 27 Nov 2023 15:17:09 +0100
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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:     Ryan Roberts <ryan.roberts@arm.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>
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From:   David Hildenbrand <david@redhat.com>
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Organization: Red Hat
In-Reply-To: <f3008ba2-82c2-47e3-9153-139a9442123b@arm.com>
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Precedence: bulk

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