linux-kernel - Re: [PATCH v5 4/7] mm: Introduce FPB_RESPECT

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Message-ID: <4afab284-5169-4837-8317-3ad216108261@arm.com>
Date: Wed, 23 Jul 2025 21:02:11 +0530
From: Dev Jain <dev.jain@....com>
To: Zi Yan <ziy@...dia.com>
Cc: akpm@...ux-foundation.org, ryan.roberts@....com, david@...hat.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
Subject: Re: [PATCH v5 4/7] mm: Introduce FPB_RESPECT_WRITE for PTE batching
 infrastructure


On 23/07/25 8:58 pm, Zi Yan wrote:
> On 18 Jul 2025, at 5:02, Dev Jain wrote:
>
>> Patch 6 optimizes mprotect() by batch clearing the ptes, masking in the new
> “Patch 6” might not make sense when reading it in the git log. Something like
> below might be better:

Andrew has fixed that for me :)

>
> mprotect() will be optimized by batch clearing the ptes, masking in the new
> protections, and batch setting the ptes in an upcoming commit.
>
> No need to repin for this one.
>
>> protections, and batch setting the ptes. Suppose that the first pte
>> of the batch is writable - with the current implementation of
>> folio_pte_batch(), it is not guaranteed that the other ptes in the batch
>> are already writable too, so we may incorrectly end up setting the
>> writable bit on all ptes via modify_prot_commit_ptes().
>>
>> Therefore, introduce FPB_RESPECT_WRITE so that all ptes in the batch
>> are writable or not.
>>
>> Signed-off-by: Dev Jain <dev.jain@....com>
>> ---
>>   mm/internal.h | 11 ++++++++---
>>   1 file changed, 8 insertions(+), 3 deletions(-)
>>
> LGTM. Reviewed-by: Zi Yan <ziy@...dia.com>

Thanks.

>
> Best Regards,
> Yan, Zi