linux-kernel - Re: [PATCH v2 3/3] mm/vma: remove mmap() retry merge

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Message-ID: <61badb6b-62aa-4457-900d-c280a8a41f97@suse.cz>
Date: Mon, 12 May 2025 15:44:25 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Andrew Morton <akpm@...ux-foundation.org>
Cc: David Hildenbrand <david@...hat.com>,
 "Liam R . Howlett" <Liam.Howlett@...cle.com>, Mike Rapoport
 <rppt@...nel.org>, Suren Baghdasaryan <surenb@...gle.com>,
 Michal Hocko <mhocko@...e.com>, Jann Horn <jannh@...gle.com>,
 Pedro Falcato <pfalcato@...e.de>, linux-fsdevel@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 Alexander Viro <viro@...iv.linux.org.uk>,
 Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
 Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH v2 3/3] mm/vma: remove mmap() retry merge

On 5/9/25 14:13, Lorenzo Stoakes wrote:
> We have now introduced a mechanism that obviates the need for a reattempted
> merge via the mmap_prepare() file hook, so eliminate this functionality
> altogether.
> 
> The retry merge logic has been the cause of a great deal of complexity in
> the past and required a great deal of careful manoeuvring of code to ensure
> its continued and correct functionality.
> 
> It has also recently been involved in an issue surrounding maple tree
> state, which again points to its problematic nature.
> 
> We make it much easier to reason about mmap() logic by eliminating this and
> simply writing a VMA once. This also opens the doors to future optimisation
> and improvement in the mmap() logic.
> 
> For any device or file system which encounters unwanted VMA fragmentation
> as a result of this change (that is, having not implemented .mmap_prepare
> hooks), the issue is easily resolvable by doing so.
> 
> Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
> Reviewed-by: David Hildenbrand <david@...hat.com>

Reviewed-by: Vlastimil Babka <vbabka@...e.cz>