linux-kernel - Re: [PATCH mm-new v3 1/3] mm/khugepaged: optimize PTE scanning with if-else-if-else-if chain

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <cfbd4f48-69a0-4ba9-bce8-f578d9602125@redhat.com>
Date: Tue, 14 Oct 2025 14:27:07 +0200
From: David Hildenbrand <david@...hat.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Lance Yang <lance.yang@...ux.dev>
Cc: akpm@...ux-foundation.org, ziy@...dia.com, baolin.wang@...ux.alibaba.com,
 Liam.Howlett@...cle.com, npache@...hat.com, ryan.roberts@....com,
 dev.jain@....com, baohua@...nel.org, ioworker0@...il.com,
 richard.weiyang@...il.com, linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH mm-new v3 1/3] mm/khugepaged: optimize PTE scanning with
 if-else-if-else-if chain

On 14.10.25 14:17, Lorenzo Stoakes wrote:
> On Wed, Oct 08, 2025 at 12:37:46PM +0800, Lance Yang wrote:
>> From: Lance Yang <lance.yang@...ux.dev>
>>
>> As pointed out by Dev, the PTE checks for disjoint conditions in the
>> scanning loops can be optimized. is_swap_pte, (pte_none && is_zero_pfn),
>> and pte_uffd_wp are mutually exclusive.
> 
> But you're not using is_swap_pte anywhere :) This comes back to my review
> quesiotn on the series this is dependent upon.
> 
>>
>> This patch refactors the loops in both __collapse_huge_page_isolate() and
>> hpage_collapse_scan_pmd() to use a continuous if-else-if-else-if chain
>> instead of separate if blocks. While at it, the redundant pte_present()
>> check before is_zero_pfn() is also removed.
> 
> I mean see review below, I don't see why you're doing this and I am
> unconvinced by how redundant that check is.
> 
> Also this just feels like it should be part of the series where you change
> these? I'm not sure why this is separate?

I think Lance is trying to unify both scanning functions to look alike, 
such that when he refactors them out in patch #3 it looks more straight 
forward.

The missing pte_present() check in hpage_collapse_scan_pmd() is interesting

Likely there is one such check missing there?

-- 
Cheers

David / dhildenb