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Date: Tue, 7 May 2024 13:42:38 +0200
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Subject: Re: [RESEND PATCH] mm: align larger anonymous mappings on THP
 boundaries
From: David Hildenbrand <david@redhat.com>
To: Ryan Roberts <ryan.roberts@arm.com>,
 Kefeng Wang <wangkefeng.wang@huawei.com>, Yang Shi <shy828301@gmail.com>
Cc: Matthew Wilcox <willy@infradead.org>,
 Yang Shi <yang@os.amperecomputing.com>, riel@surriel.com, cl@linux.com,
 akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org,
 Ze Zuo <zuoze1@huawei.com>
References: <20231214223423.1133074-1-yang@os.amperecomputing.com>
 <1e8f5ac7-54ce-433a-ae53-81522b2320e1@arm.com>
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 <dea802da-2e5e-4c91-b817-43afdde68958@huawei.com>
 <1dc9a561-55f7-4d65-8b86-8a40fa0e84f9@arm.com>
 <6016c0e9-b567-4205-8368-1f1c76184a28@huawei.com>
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 <4e7ce57f-cad1-44d5-a1d8-4cd47683a358@arm.com>
 <9ce8a0f4-d1af-44ea-87b5-57ebdb3d2910@arm.com>
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On 07.05.24 13:34, David Hildenbrand wrote:
> On 07.05.24 13:26, Ryan Roberts wrote:
>> On 07/05/2024 12:14, Ryan Roberts wrote:
>>> On 07/05/2024 12:13, David Hildenbrand wrote:
>>>>
>>>>> https://github.com/intel/lmbench/blob/master/src/lat_mem_rd.c#L95
>>>>>
>>>>>> suggest. If you want to try something semi-randomly; it might be useful to rule
>>>>>> out the arm64 contpte feature. I don't see how that would be interacting here if
>>>>>> mTHP is disabled (is it?). But its new for 6.9 and arm64 only. Disable with
>>>>>> ARM64_CONTPTE (needs EXPERT) at compile time.
>>>>> I don't enabled mTHP, so it should be not related about ARM64_CONTPTE,
>>>>> but will have a try.
>>>>
>>>> cont-pte can get active if we're just lucky when allocating pages in the right
>>>> order, correct Ryan?
>>>
>>> No it shouldn't do; it requires the pages to be in the same folio.
> 
> Ah, my memory comes back. That's also important for folio_pte_batch() to
> currently work as expected I think. We could change that, though, and
> let cont-pte batch across folios.

Thinking about it (and trying to refresh my memories), access/dirty bits 
might be why we don't want to do that.

-- 
Cheers,

David / dhildenb