Re: [PATCHv5] mm/gup: speed up check_and_migrate_cma_pages() on huge page

[Pingfan Liu <kernelfans@gmail.com>]

On Fri, Jun 28, 2019 at 7:25 AM Andrew Morton <akpm@linux-foundation.org> wrote:
>
> On Thu, 27 Jun 2019 13:15:45 +0800 Pingfan Liu <kernelfans@gmail.com> wrote:
>
> > Both hugetlb and thp locate on the same migration type of pageblock, since
> > they are allocated from a free_list[]. Based on this fact, it is enough to
> > check on a single subpage to decide the migration type of the whole huge
> > page. By this way, it saves (2M/4K - 1) times loop for pmd_huge on x86,
> > similar on other archs.
> >
> > Furthermore, when executing isolate_huge_page(), it avoid taking global
> > hugetlb_lock many times, and meanless remove/add to the local link list
> > cma_page_list.
> >
>
> Thanks, looks good to me.  Have any timing measurements been taken?
Not yet. It is a little hard to force huge page to be allocated CMA
area. Should I provide the measurements?
>
> > ...
> >
> > --- a/mm/gup.c
> > +++ b/mm/gup.c
> > @@ -1336,25 +1336,30 @@ static long check_and_migrate_cma_pages(struct task_struct *tsk,
> >                                       struct vm_area_struct **vmas,
> >                                       unsigned int gup_flags)
> >  {
> > -     long i;
> > +     long i, step;
>
> I'll make these variables unsigned long - to match nr_pages and because
> we have no need for them to be negative.
OK, will fix it.

Thanks,
  Pingfan
>
> > ...