Re: [PATCH v2 3/4] mm: Introduce page_needs_cow_for_dma() for deciding whether cow

Linus Torvalds
2021-02-04T17:56:56Z

On Thu, Feb 4, 2021 at 6:50 AM Peter Xu <peterx@redhat.com> wrote:
>
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1291,6 +1291,27 @@ static inline bool page_maybe_dma_pinned(struct page *page)
> GUP_PIN_COUNTING_BIAS;
> }
>
> +static inline bool is_cow_mapping(vm_flags_t flags)
> +{
> + return (flags & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE;
> +}

Oh, and I just realized: moving this to <linux/mm.h> means that this
patch could/should also get rid of

- manual copy of this in mm/hugetlb.c:

cow = (vma->vm_flags & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE;

- private #define for the same thing in fs/proc/task_mmu.c

#define is_cow_mapping(flags) (((flags) & (VM_SHARED |
VM_MAYWRITE)) == VM_MAYWRITE)

- manual copy in drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c:

bool is_cow_mapping =
(vma->vm_flags & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE;

I guess it could be a later cleanup patch too, but maybe best done in
this series just to not forget about it.

Linus