linux-kernel - Re: [PATCHv2] mm/gup: speed up check_and_migrate_cma

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Date:   Mon, 24 Jun 2019 13:32:34 +0800
From:   Pingfan Liu <kernelfans@...il.com>
To:     Ira Weiny <ira.weiny@...el.com>
Cc:     Linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        John Hubbard <jhubbard@...dia.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Christoph Hellwig <hch@....de>,
        Keith Busch <keith.busch@...el.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        LKML <Linux-kernel@...r.kernel.org>
Subject: Re: [PATCHv2] mm/gup: speed up check_and_migrate_cma_pages() on huge page

On Mon, Jun 24, 2019 at 12:43 PM Ira Weiny <ira.weiny@...el.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@...il.com>
> > Cc: Andrew Morton <akpm@...ux-foundation.org>
> > Cc: Ira Weiny <ira.weiny@...el.com>
> > Cc: Mike Rapoport <rppt@...ux.ibm.com>
> > Cc: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
> > Cc: Thomas Gleixner <tglx@...utronix.de>
> > Cc: John Hubbard <jhubbard@...dia.com>
> > Cc: "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
> > Cc: Christoph Hellwig <hch@....de>
> > Cc: Keith Busch <keith.busch@...el.com>
> > Cc: Mike Kravetz <mike.kravetz@...cle.com>
> > Cc: Linux-kernel@...r.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?

Thanks,
  Pingfan
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