linux-kernel - Re: [RFC PATCH 3/3] mm/mincore: avoid touching the PTL

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Message-ID: <CAG48ez114_bmuca2UL-g0ZY76-VqhL-4rQtJM_k0N2NJXE4vdg@mail.gmail.com>
Date: Thu, 7 Aug 2025 18:02:17 +0200
From: Jann Horn <jannh@...gle.com>
To: Kairui Song <kasong@...cent.com>
Cc: linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>, 
	"Liam R. Howlett" <Liam.Howlett@...cle.com>, Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, 
	Vlastimil Babka <vbabka@...e.cz>, Pedro Falcato <pfalcato@...e.de>, Matthew Wilcox <willy@...radead.org>, 
	Hugh Dickins <hughd@...gle.com>, David Hildenbrand <david@...hat.com>, Chris Li <chrisl@...nel.org>, 
	Barry Song <baohua@...nel.org>, Baoquan He <bhe@...hat.com>, Nhat Pham <nphamcs@...il.com>, 
	Kemeng Shi <shikemeng@...weicloud.com>, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 3/3] mm/mincore: avoid touching the PTL

On Thu, Aug 7, 2025 at 5:27 PM Kairui Song <ryncsn@...il.com> wrote:
> mincore only interested in the existence of a page, which is a
> changing state by nature, locking and making it stable is not needed.
> And now neither mincore_page or mincore_swap requires PTL, this PTL
> locking can be dropped.

This means you can race such that you end up looking at an unrelated
page of another process, right? And your patch intentionally allows
that to happen in order to make mincore() faster?