linux-kernel - Re: [RESEND PATCH] mm: align larger anonymous mappings on THP boundaries

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Message-ID: <adc6ac88-8fb8-44ad-abe6-9e9f9e4017e3@redhat.com>
Date: Tue, 7 May 2024 13:42:38 +0200
From: David Hildenbrand <david@...hat.com>
To: Ryan Roberts <ryan.roberts@....com>,
 Kefeng Wang <wangkefeng.wang@...wei.com>, Yang Shi <shy828301@...il.com>
Cc: Matthew Wilcox <willy@...radead.org>,
 Yang Shi <yang@...amperecomputing.com>, riel@...riel.com, cl@...ux.com,
 akpm@...ux-foundation.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 Ze Zuo <zuoze1@...wei.com>
Subject: Re: [RESEND PATCH] mm: align larger anonymous mappings on THP
 boundaries

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