linux-kernel - Re: [PATCH 1/1] mm/khugepaged: bypassing unnecessary scans with MMF_DISABLE

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Message-ID: <ZbfSP6xt6JAE2NrH@tiehlicka>
Date: Mon, 29 Jan 2024 17:28:47 +0100
From: Michal Hocko <mhocko@...e.com>
To: Lance Yang <ioworker0@...il.com>
Cc: akpm@...ux-foundation.org, zokeefe@...gle.com, david@...hat.com,
	songmuchun@...edance.com, shy828301@...il.com, peterx@...hat.com,
	minchan@...nel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] mm/khugepaged: bypassing unnecessary scans with
 MMF_DISABLE_THP check

On Mon 29-01-24 13:45:51, Lance Yang wrote:
> khugepaged scans the entire address space in the
> background for each given mm, looking for
> opportunities to merge sequences of basic pages
> into huge pages. However, when an mm is inserted
> to the mm_slots list, and the MMF_DISABLE_THP flag
> is set later, this scanning process becomes
> unnecessary for that mm and can be skipped to avoid
> redundant operations, especially in scenarios with
> a large address space.

Is this a real problem? I thought that the prctl is called
on the parent before fork/exec. Or are you aware of any
applications which do call prctl late enough that the race
would be actually observable?
-- 
Michal Hocko
SUSE Labs