Re: [PATCH v5 14/38] mm/vma: add vma[_flags]_is_mm_managed() predicates

["David Hildenbrand (Arm)" <david@kernel.org>]

On 10/9/26 20:04, Lorenzo Stoakes (ARM) wrote:
> Rather than referring to VMA flags with uncertain meaning, add a new
> predicate that explicitly describes what absence of the VMA_PFNMAP_BIT and
> VMA_MIXEDMAP_BIT flags means, and then refer to that function for
> determining VMA mergeability.
> 
> If neither of these flags are set, that means the contents of the mapping
> are managed by core mm.
> 
> Otherwise they are instead owned by some other kernel component, usually a
> driver: the memory may be MMIO, kernel-allocated pages or even ordinary
> pages the driver maps itself, but core mm must not populate, reclaim,
> migrate, copy-on-write or merge the range itself.
> 
> We initially also treat VMA_IO_BIT as implying a mapping is not mm-managed,
> as by implication it cannot be. (mlock() also sets VMA_IO_BIT transiently
> on ordinary VMAs while locking them, which is addressed later in this
> series.)
> 
> However the intent is to in future remove this, as no mapping should be
> marked as an I/O mapping without also being marked with VMA_PFNMAP_BIT.
> 
> This forms the basis of further work intended to improve how we express VMA
> properties such as this.
> 
> Also update the VMA userland tests to reflect the change.
> 
> No functional change intended.
> 
> Reviewed-by: Zi Yan <ziy@nvidia.com>
> Reviewed-by: Suren Baghdasaryan <surenb@google.com>
> Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
> ---
>  include/linux/mm.h              | 53 ++++++++++++++++++++++++++++++++++++++++-
>  tools/testing/vma/include/dup.h | 29 +++++++++++++++++++++-
>  2 files changed, 80 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 97e1eb4fe3a4..83953757735a 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1612,6 +1612,41 @@ static inline bool vma_is_shared_maywrite(const struct vm_area_struct *vma)
>  	return is_shared_maywrite(&vma->flags);
>  }
>  
> +/**
> + * vma_flags_is_mm_managed() - Do the specified VMA flags indicate that the
> + * contents of the VMA are managed by core mm?
> + * @flags: The VMA flags to test.
> + *
> + * Such a mapping is one established by a simple mmap() or brk() with no driver
> + * or other kernel component involved.
> + *
> + * They are rmappable, and core mm services rmap operations including reclaim,
> + * as well as population, CoW and merge/split (if eligible).

I assume ->fault returning some kernel allocations (VM_DONTEXPAND set but none
of the others) will currently contradict to that. But hopefully we'll clean that
up in the future (or improve the documentation to cover them as well).

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

-- 
Cheers,

David