linux-kernel - Re: [PATCH v3 1/5] mm: Optimize mprotect() by batch-skipping PTEs

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Message-ID: <4f97491c-b0dd-406a-9ddb-4f4424571704@arm.com>
Date: Thu, 22 May 2025 13:17:02 +0530
From: Dev Jain <dev.jain@....com>
To: David Hildenbrand <david@...hat.com>, akpm@...ux-foundation.org
Cc: ryan.roberts@....com, willy@...radead.org, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, catalin.marinas@....com, will@...nel.org,
 Liam.Howlett@...cle.com, lorenzo.stoakes@...cle.com, vbabka@...e.cz,
 jannh@...gle.com, anshuman.khandual@....com, peterx@...hat.com,
 joey.gouly@....com, ioworker0@...il.com, baohua@...nel.org,
 kevin.brodsky@....com, quic_zhenhuah@...cinc.com,
 christophe.leroy@...roup.eu, yangyicong@...ilicon.com,
 linux-arm-kernel@...ts.infradead.org, hughd@...gle.com,
 yang@...amperecomputing.com, ziy@...dia.com
Subject: Re: [PATCH v3 1/5] mm: Optimize mprotect() by batch-skipping PTEs


On 22/05/25 12:43 pm, David Hildenbrand wrote:
>
>>> ... likely with a better function name,
>>
>>
>> I want to be able to reuse the folio from vm_normal_folio(), and we also
>> need
>>
>> nr_ptes to know how much to skip, so if there is no objection in passing
>> int *nr_ptes,
>>
>> or struct folio **foliop to this new function, then I'll carry on with
>> your suggestion :)
>
> Can you quickly prototype what you have in mind and paste it here? 
> Will make it easier :)


if (prot_numa)

     func(vma, addr, oldpte, &nr);


struct folio *folio func(vma, addr, oldpte, int *nr)

{

     if (pte_protnone(oldpte))

         *nr = 1, return NULL;

     folio = vm_normal_folio();

     if (!folio)

         *nr =1, return NULL;

     if the other skipping conditions happen, goto skip_batch, return 
folio and set *nr = batch


     if (sysctl.....) {

skip_batch:

     *nr = mprotect_batch();

}

     if (folio_use_access_time)....

     return folio;

}