linux-kernel - Re: [PATCH v2 1/2] mm: propagate VM

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Message-ID: <CANaxB-yqnMEP3zkoPcY8cHNh66UfHb8PNs9s7judRyJ8JC20pA@mail.gmail.com>
Date: Mon, 17 Nov 2025 09:52:52 -0800
From: Andrei Vagin <avagin@...il.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, David Hildenbrand <david@...nel.org>, 
	"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>, 
	Jann Horn <jannh@...gle.com>, Pedro Falcato <pfalcato@...e.de>, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] mm: propagate VM_SOFTDIRTY on merge

On Mon, Nov 17, 2025 at 9:40 AM Lorenzo Stoakes
<lorenzo.stoakes@...cle.com> wrote:
>
> Currently we set VM_SOFTDIRTY when a new mapping is set up (whether by
> establishing a new VMA, or via merge) as implemented in __mmap_complete()
> and do_brk_flags().
>
> However, when performing a merge of existing mappings such as when
> performing mprotect(), we may lose the VM_SOFTDIRTY flag.
>
> This is because currently we simply ignore VM_SOFTDIRTY for the purposes
> of merge, so one VMA may possess the flag and another not, and whichever
> happens to be the target VMA will be the one upon which the merge is
> performed which may or may not have VM_SOFTDIRTY set.
>
> Now we have the concept of 'sticky' VMA flags, let's make VM_SOFTDIRTY one
> which solves this issue.
>
> Additionally update VMA userland tests to propagate changes.
>
> Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
> Suggested-by: Vlastimil Babka <vbabka@...e.cz>
> Acked-by: David Hildenbrand (Red Hat) <david@...nel.org>
> Reviewed-by: Pedro Falcato <pfalcato@...e.de>

Acked-by: Andrey Vagin <avagin@...il.com>

Thanks,
Andrei