linux-kernel - Re: [DISCUSSION] Unconditionally lock folios when calling rmap

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Message-ID: <13fca620-437f-4105-b4bd-5b0f4e9f064b@lucifer.local>
Date: Fri, 22 Aug 2025 19:08:08 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Matthew Wilcox <willy@...radead.org>
Cc: Lokesh Gidra <lokeshgidra@...gle.com>,
        David Hildenbrand <david@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Harry Yoo <harry.yoo@...cle.com>, Zi Yan <ziy@...dia.com>,
        Barry Song <21cnbao@...il.com>,
        "open list:MEMORY MANAGEMENT" <linux-mm@...ck.org>,
        Peter Xu <peterx@...hat.com>, Suren Baghdasaryan <surenb@...gle.com>,
        Kalesh Singh <kaleshsingh@...gle.com>,
        android-mm <android-mm@...gle.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Jann Horn <jannh@...gle.com>, Rik van Riel <riel@...riel.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>
Subject: Re: [DISCUSSION] Unconditionally lock folios when calling rmap_walk()

On Fri, Aug 22, 2025 at 06:44:13PM +0100, Matthew Wilcox wrote:
> On Fri, Aug 22, 2025 at 10:29:52AM -0700, Lokesh Gidra wrote:
> > Currently, some callers of rmap_walk() conditionally avoid try-locking
> > non-ksm anon folios. This necessitates serialization through anon_vma
>
> ... this seems awfully familiar.  Why did you send it again after
> a bunch of people had already said useful things on that thread?

This is on me - I asked him to resend because the original was mislabelled and
didn't cc the right people, and lei blew up when I tried to grab it, so I asked
various people to hold off on reply/resend replies on resent thread and asked
Lokesh to resend.

Apologies for loss of context. rmap locking is important to me as it is deeply
sensitive and has caused numerous painful issues in the past so want to make
sure myself, David and the reivewers are all included.

Cheers, Lorenzo