linux-kernel - Re: [PATCH 0/2] make VM_SOFTDIRTY a sticky VMA flag

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Message-Id: <20251114135303.878b52f6db3dea4596f4c11a@linux-foundation.org>
Date: Fri, 14 Nov 2025 13:53:03 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: 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 0/2] make VM_SOFTDIRTY a sticky VMA flag

On Fri, 14 Nov 2025 17:53:17 +0000 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.
> 

userspace-visible effects?

Documentation/admin-guide/mm/soft-dirty.rst tells me that this can
already happen in other circumstances so I guess it isn't very serious.
CRIU inefficiency.  perhaps?

Please review Documentation/admin-guide/mm/soft-dirty.rst, check that
it is complete and accurate?