linux-kernel - Re: [PATCH v4 3/9] mm: update vma_modify_flags() to handle residual flags, document

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Message-ID: <89778199-d4c9-4b0e-9e6d-64c9a23e1287@suse.cz>
Date: Wed, 19 Nov 2025 17:27:47 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Andrew Morton <akpm@...ux-foundation.org>
Cc: Jonathan Corbet <corbet@....net>, 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>, Steven Rostedt <rostedt@...dmis.org>,
 Masami Hiramatsu <mhiramat@...nel.org>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Jann Horn <jannh@...gle.com>, Pedro Falcato <pfalcato@...e.de>,
 Zi Yan <ziy@...dia.com>, Baolin Wang <baolin.wang@...ux.alibaba.com>,
 Nico Pache <npache@...hat.com>, Ryan Roberts <ryan.roberts@....com>,
 Dev Jain <dev.jain@....com>, Barry Song <baohua@...nel.org>,
 Lance Yang <lance.yang@...ux.dev>, linux-kernel@...r.kernel.org,
 linux-fsdevel@...r.kernel.org, linux-doc@...r.kernel.org,
 linux-mm@...ck.org, linux-trace-kernel@...r.kernel.org,
 linux-kselftest@...r.kernel.org, Andrei Vagin <avagin@...il.com>
Subject: Re: [PATCH v4 3/9] mm: update vma_modify_flags() to handle residual
 flags, document

On 11/18/25 11:17, Lorenzo Stoakes wrote:
> The vma_modify_*() family of functions each either perform splits, a merge
> or no changes at all in preparation for the requested modification to
> occur.
> 
> When doing so for a VMA flags change, we currently don't account for any
> flags which may remain (for instance, VM_SOFTDIRTY) despite the requested
> change in the case that a merge succeeded.
> 
> This is made more important by subsequent patches which will introduce the
> concept of sticky VMA flags which rely on this behaviour.
> 
> This patch fixes this by passing the VMA flags parameter as a pointer and
> updating it accordingly on merge and updating callers to accommodate for
> this.
> 
> Additionally, while we are here, we add kdocs for each of the
> vma_modify_*() functions, as the fact that the requested modification is
> not performed is confusing so it is useful to make this abundantly
> clear.
> 
> We also update the VMA userland tests to account for this change.
> 
> Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>

LGTM (where the "good" means "correct" (*), not "nice", which is however not
a fault of the patch but the pre-existing code :)

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

(*) but it's likely there will be a fix needed, whenever I conclude this