linux-kernel - Re: [PATCH 2/2] mm/rmap: Improve mlock tracking for large folios

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Message-ID: <thknnu35aqusupqt5rin4vmach3vb3ukyyaowdegtww2mvmrom@zck5s5bzj4vx>
Date: Thu, 18 Sep 2025 12:32:12 -0700
From: Shakeel Butt <shakeel.butt@...ux.dev>
To: kirill@...temov.name
Cc: Andrew Morton <akpm@...ux-foundation.org>, 
	David Hildenbrand <david@...hat.com>, Hugh Dickins <hughd@...gle.com>, 
	Matthew Wilcox <willy@...radead.org>, Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, 
	"Liam R. Howlett" <Liam.Howlett@...cle.com>, Vlastimil Babka <vbabka@...e.cz>, 
	Mike Rapoport <rppt@...nel.org>, Suren Baghdasaryan <surenb@...gle.com>, 
	Michal Hocko <mhocko@...e.com>, Rik van Riel <riel@...riel.com>, 
	Harry Yoo <harry.yoo@...cle.com>, Johannes Weiner <hannes@...xchg.org>, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org, Kiryl Shutsemau <kas@...nel.org>
Subject: Re: [PATCH 2/2] mm/rmap: Improve mlock tracking for large folios

On Thu, Sep 18, 2025 at 12:21:57PM +0100, kirill@...temov.name wrote:
> From: Kiryl Shutsemau <kas@...nel.org>
> 
> The kernel currently does not mlock large folios when adding them to
> rmap, stating that it is difficult to confirm that the folio is fully
> mapped and safe to mlock it. However, nowadays the caller passes a
> number of pages of the folio that are getting mapped, making it easy to
> check if the entire folio is mapped to the VMA.
> 
> mlock the folio on rmap if it is fully mapped to the VMA.
> 
> Signed-off-by: Kiryl Shutsemau <kas@...nel.org>

Acked-by: Shakeel Butt <shakeel.butt@...ux.dev>

It would be interesting to state how this specific issue was causing
problems in our production particularly for workloads that were doing
load shedding based on mlock stats.