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

[Pingfan Liu <kernelfans@gmail.com>]

On Mon, Jun 24, 2019 at 1:32 PM Pingfan Liu <kernelfans@gmail.com> wrote:
>
> On Mon, Jun 24, 2019 at 12:43 PM Ira Weiny <ira.weiny@intel.com> 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@gmail.com>
> > > Cc: Andrew Morton <akpm@linux-foundation.org>
> > > Cc: Ira Weiny <ira.weiny@intel.com>
> > > Cc: Mike Rapoport <rppt@linux.ibm.com>
> > > Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
> > > Cc: Thomas Gleixner <tglx@linutronix.de>
> > > Cc: John Hubbard <jhubbard@nvidia.com>
> > > Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
> > > Cc: Christoph Hellwig <hch@lst.de>
> > > Cc: Keith Busch <keith.busch@intel.com>
> > > Cc: Mike Kravetz <mike.kravetz@oracle.com>
> > > Cc: Linux-kernel@vger.kernel.org
> > > ---
> > >  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?
>
Oh, got it. It should be 1<<compound_order(head)
> Thanks,
>   Pingfan
> [...]