Re: [PATCH v4 3/5] mm: Introduce page_needs_cow_for_dma() for deciding whether cow

[Jason Gunthorpe]

On Mon, Feb 08, 2021 at 10:02:27PM -0500, Peter Xu wrote:
> We've got quite a few places (pte, pmd, pud) that explicitly checked against
> whether we should break the cow right now during fork().  It's easier to
> provide a helper, especially before we work the same thing on hugetlbfs.
> 
> Since we'll reference is_cow_mapping() in mm.h, move it there too.  Actually it
> suites mm.h more since internal.h is mm/ only, but mm.h is exported to the
> whole kernel.  With that we should expect another patch to use is_cow_mapping()
> whenever we can across the kernel since we do use it quite a lot but it's
> always done with raw code against VM_* flags.
> 
> Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
> ---
>  include/linux/mm.h | 21 +++++++++++++++++++++
>  mm/huge_memory.c   |  8 ++------
>  mm/internal.h      |  5 -----
>  mm/memory.c        |  8 +-------
>  4 files changed, 24 insertions(+), 18 deletions(-)

Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>

Jason