Re: [PATCH v2 1/2] mm: propagate VM_SOFTDIRTY on merge

[Andrei Vagin]

On Mon, Nov 17, 2025 at 9:40 AM Lorenzo Stoakes
<lorenzo.stoakes@xxxxxxxxxx> 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@xxxxxxxxxx>
> Suggested-by: Vlastimil Babka <vbabka@xxxxxxx>
> Acked-by: David Hildenbrand (Red Hat) <david@xxxxxxxxxx>
> Reviewed-by: Pedro Falcato <pfalcato@xxxxxxx>

Acked-by: Andrey Vagin <avagin@xxxxxxxxx>

Thanks,
Andrei