Re: [PATCH v6 30/39] mm/vma: introduce vma[_flags]_is_mm_backed()

On 10/13/26 17:05, Lorenzo Stoakes (ARM) wrote:

Introduce vma[_flags]_is_mm_backed() for the purposes of identifying
mappings which are mm-managed and whose contents were placed there by core
mm's own fault path - rather than a custom ->fault handler.

Mappings not managed by core mm do not fall into this category, as they are
populated by their owner, and nor of course does memory-mapped I/O.

We exclude fixed mappings as these have a layout core mm cannot assume
ordinary fault semantics over.

hugetlb mappings are fixed mappings, but core mm owns them entirely, so
they are explicitly carved out as mm-backed, as the MADV_DODUMP check
already does.

Use this functionality to update the madvise MADV_DODUMP check to test for
this rather than open-coding it.

Also update vma_flags_can_merge() so it is written in terms of
vma_flags_is_mm_backed() - all mm-backed mappings can be merged except
hugetlb mappings, whose flags and fields do not completely describe them.

Also update __thp_vma_allowable_orders() to use vma_is_mm_backed() rather
than testing for mergeability, which is irrelevant to this function.

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
mm-managed mappings may not set VMA_IO_BIT, so we implicitly include
these.

No functional change intended.

Acked-by: Zi Yan <ziy@nvidia.com>
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---

Acked-by: David Hildenbrand (Arm) <david@kernel.org>

-- 
Cheers,

David