Re: [PATCH] mm/gup: remove unnecessary check against CMA in __gup_longterm_locked()

[Pingfan Liu <kernelfans@xxxxxxxxx>]

On Tue, Jun 4, 2019 at 4:30 PM Aneesh Kumar K.V
<aneesh.kumar@xxxxxxxxxxxxx> wrote:
>
> On 6/4/19 12:56 PM, Pingfan Liu wrote:
> > The PF_MEMALLOC_NOCMA is set by memalloc_nocma_save(), which is finally
> > cast to ~_GFP_MOVABLE.  So __get_user_pages_locked() will get pages from
> > non CMA area and pin them.  There is no need to
> > check_and_migrate_cma_pages().
>
>
> That is not completely correct. We can fault in that pages outside
> get_user_pages_longterm at which point those pages can get allocated
> from CMA region. memalloc_nocma_save() as added as an optimization to
> avoid unnecessary page migration.
Yes, you are right.

Thanks,
  Pingfan