linux-kernel - Re: [PATCH 1/3] mm/vma: fix incorrectly disallowed anonymous VMA merges

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Message-ID: <fb1a0025-ed51-4729-bf6a-34277afc0822@lucifer.local>
Date: Mon, 7 Apr 2025 17:44:26 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Wei Yang <richard.weiyang@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>, Jann Horn <jannh@...gle.com>,
        "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        David Hildenbrand <david@...hat.com>,
        Matthew Wilcox <willy@...radead.org>, Rik van Riel <riel@...riel.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] mm/vma: fix incorrectly disallowed anonymous VMA
 merges

On Mon, Apr 07, 2025 at 11:24:19AM +0100, Lorenzo Stoakes wrote:
> Since you seem dead-set on this issue, I think the best solution here is
> just for me to update the comment a little. I'll send a fix-patch.

Actually, re-reading the comment I added:

 * If, at any point, the VMA had unCoW'd mappings from parents, it will maintain
 * more than one anon_vma_chain connecting it to more than one anon_vma. A merge
 * would mean a wider range of folios sharing the root anon_vma lock, and thus
 * potential lock contention, we do not wish to encourage merging such that this
 * scales to a problem.

'If _at any point_' - we already clarify the situation.

So I don't think any change is required here, sorry.