linux-kernel - Re: [RFC 2/2] khugepaged: use upgrade_read() to optimize collapse_huge

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: <20241017061841.81240-1-lizhe.67@bytedance.com>
Date: Thu, 17 Oct 2024 14:18:41 +0800
From: lizhe.67@...edance.com
To: willy@...radead.org
Cc: akpm@...ux-foundation.org,
	boqun.feng@...il.com,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	lizhe.67@...edance.com,
	longman@...hat.com,
	mingo@...hat.com,
	peterz@...radead.org,
	will@...nel.org
Subject: Re: [RFC 2/2] khugepaged: use upgrade_read() to optimize collapse_huge_page

On Wed, 16 Oct 2024 12:53:15 +0100, willy@...radead.org wrote:

>On Wed, Oct 16, 2024 at 12:36:00PM +0800, lizhe.67@...edance.com wrote:
>> From: Li Zhe <lizhe.67@...edance.com>
>> 
>> In function collapse_huge_page(), we drop mmap read lock and get
>> mmap write lock to prevent most accesses to pagetables. There is
>> a small time window to allow other tasks to acquire the mmap lock.
>> With the use of upgrade_read(), we don't need to check vma and pmd
>> again in most cases.
>
>This is clearly a performance optimisation.  So you must have some
>numebrs that justify this, please include them.

Yes, I will add the relevant data to v2 patch.

Thanks!