Re: [PATCHv2] mm/gup: speed up check_and_migrate_cma_pages() on huge page

[Pingfan Liu]

On Mon, Jun 24, 2019 at 12:43 PM Ira Weiny <ira.weiny@xxxxxxxxx> wrote:
>
> On Mon, Jun 24, 2019 at 12:12:41PM +0800, Pingfan Liu 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.
> >
> > Signed-off-by: Pingfan Liu <kernelfans@xxxxxxxxx>
> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > Cc: Ira Weiny <ira.weiny@xxxxxxxxx>
> > Cc: Mike Rapoport <rppt@xxxxxxxxxxxxx>
> > Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > Cc: John Hubbard <jhubbard@xxxxxxxxxx>
> > Cc: "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxx>
> > Cc: Christoph Hellwig <hch@xxxxxx>
> > Cc: Keith Busch <keith.busch@xxxxxxxxx>
> > Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> > Cc: Linux-kernel@xxxxxxxxxxxxxxx
> > ---
> >  mm/gup.c | 19 ++++++++++++-------
> >  1 file changed, 12 insertions(+), 7 deletions(-)
> >
> > diff --git a/mm/gup.c b/mm/gup.c
> > index ddde097..544f5de 100644
> > --- a/mm/gup.c
> > +++ b/mm/gup.c
> > @@ -1342,19 +1342,22 @@ static long check_and_migrate_cma_pages(struct task_struct *tsk,
> >       LIST_HEAD(cma_page_list);
> >
> >  check_again:
> > -     for (i = 0; i < nr_pages; i++) {
> > +     for (i = 0; i < nr_pages;) {
> > +
> > +             struct page *head = compound_head(pages[i]);
> > +             long step = 1;
> > +
> > +             if (PageCompound(head))
> > +                     step = compound_order(head) - (pages[i] - head);
>
> Sorry if I missed this last time.  compound_order() is not correct here.
For thp, prep_transhuge_page()->prep_compound_page()->set_compound_order().
For smaller hugetlb,
prep_new_huge_page()->prep_compound_page()->set_compound_order().
For gigantic page, prep_compound_gigantic_page()->set_compound_order().

Do I miss anything?

Thanks,
  Pingfan
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