Re: [PATCH v3 31/40] mm/vma: introduce vma[_flags]_is_persistent()

[Zi Yan]

On Thu Sep 17, 2026 at 12:22 PM EDT, Lorenzo Stoakes (ARM) wrote:
> Introduce vma[_flags]_is_persistent() for the purposes of identifying
> mappings that are persistent in the sense that bytes to the mapping stay
> there, and bytes read from the mapping are the same unless changed by
> actions taken by userland.
>
> Kernel-owned mappings do not fall into this category, as their owner may
> change the contents without the user having initiated it, and nor of course
> does memory-mapped I/O.
>
> We exclude fixed mappings as these are singled out as being unmergeable and
> so cannot be guaranteed to persist user data.
>
> hugetlb mappings are fixed mappings, but their contents are entirely the
> user's, so they are explicitly carved out as persistent, as the MADV_DODUMP
> check already does.
>
> It excludes droppable mappings, which by their nature are ephemeral.
>
> Use this functionality to update the madvise MADV_DODUMP check to test for
> persistence rather than open-coding this.
>
> This replaces the VM_SPECIAL check which means it no longer checks for
> VMA_IO_BIT, however this is safe as we have established the invariant that
> only kernel-owned mappings may set VMA_IO_BIT, so we implicitly include
> these.
>
> No functional change intended.
>
> Signed-off-by: Lorenzo Stoakes (ARM) <ljs@xxxxxxxxxx>
> ---
>  include/linux/mm.h | 44 ++++++++++++++++++++++++++++++++++++++++++++
>  mm/madvise.c       |  4 ++--
>  2 files changed, 46 insertions(+), 2 deletions(-)
>

LGTM.

Acked-by: Zi Yan <ziy@xxxxxxxxxx>


-- 
Best Regards,
Yan, Zi