linux-kernel - Re: [PATCH 6/6] mm/gup: migrate pinned pages out of movable zone

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Date:   Fri, 4 Dec 2020 12:43:29 -0500
From:   Pavel Tatashin <pasha.tatashin@...een.com>
To:     Joonsoo Kim <js1304@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Michal Hocko <mhocko@...e.com>,
        David Hildenbrand <david@...hat.com>,
        Oscar Salvador <osalvador@...e.de>,
        Dan Williams <dan.j.williams@...el.com>,
        Sasha Levin <sashal@...nel.org>,
        Tyler Hicks <tyhicks@...ux.microsoft.com>,
        mike.kravetz@...cle.com, Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>, Jason Gunthorpe <jgg@...pe.ca>,
        Peter Zijlstra <peterz@...radead.org>,
        Mel Gorman <mgorman@...e.de>,
        Matthew Wilcox <willy@...radead.org>,
        David Rientjes <rientjes@...gle.com>,
        John Hubbard <jhubbard@...dia.com>
Subject: Re: [PATCH 6/6] mm/gup: migrate pinned pages out of movable zone

On Thu, Dec 3, 2020 at 11:14 PM Joonsoo Kim <js1304@...il.com> wrote:
>
> On Wed, Dec 02, 2020 at 12:23:30AM -0500, Pavel Tatashin wrote:
> > We do not allocate pin pages in ZONE_MOVABLE, but if pages were already
> > allocated before pinning they need to migrated to a different zone.
> > Currently, we migrate movable CMA pages only. Generalize the function
> > that migrates CMA pages to migrate all movable pages.
> >
> > Signed-off-by: Pavel Tatashin <pasha.tatashin@...een.com>
> > ---
> >  include/linux/migrate.h        |  1 +
> >  include/trace/events/migrate.h |  3 +-
> >  mm/gup.c                       | 56 +++++++++++++---------------------
> >  3 files changed, 24 insertions(+), 36 deletions(-)
> >
> > diff --git a/include/linux/migrate.h b/include/linux/migrate.h
> > index 0f8d1583fa8e..00bab23d1ee5 100644
> > --- a/include/linux/migrate.h
> > +++ b/include/linux/migrate.h
> > @@ -27,6 +27,7 @@ enum migrate_reason {
> >       MR_MEMPOLICY_MBIND,
> >       MR_NUMA_MISPLACED,
> >       MR_CONTIG_RANGE,
> > +     MR_LONGTERM_PIN,
> >       MR_TYPES
> >  };
> >
> > diff --git a/include/trace/events/migrate.h b/include/trace/events/migrate.h
> > index 4d434398d64d..363b54ce104c 100644
> > --- a/include/trace/events/migrate.h
> > +++ b/include/trace/events/migrate.h
> > @@ -20,7 +20,8 @@
> >       EM( MR_SYSCALL,         "syscall_or_cpuset")            \
> >       EM( MR_MEMPOLICY_MBIND, "mempolicy_mbind")              \
> >       EM( MR_NUMA_MISPLACED,  "numa_misplaced")               \
> > -     EMe(MR_CONTIG_RANGE,    "contig_range")
> > +     EM( MR_CONTIG_RANGE,    "contig_range")                 \
> > +     EMe(MR_LONGTERM_PIN,    "longterm_pin")
> >
> >  /*
> >   * First define the enums in the above macros to be exported to userspace
> > diff --git a/mm/gup.c b/mm/gup.c
> > index 724d8a65e1df..1d511f65f8a7 100644
> > --- a/mm/gup.c
> > +++ b/mm/gup.c
> > @@ -1593,19 +1593,18 @@ static bool check_dax_vmas(struct vm_area_struct **vmas, long nr_pages)
> >  }
> >  #endif
> >
> > -#ifdef CONFIG_CMA
> > -static long check_and_migrate_cma_pages(struct mm_struct *mm,
> > -                                     unsigned long start,
> > -                                     unsigned long nr_pages,
> > -                                     struct page **pages,
> > -                                     struct vm_area_struct **vmas,
> > -                                     unsigned int gup_flags)
> > +static long check_and_migrate_movable_pages(struct mm_struct *mm,
> > +                                         unsigned long start,
> > +                                         unsigned long nr_pages,
> > +                                         struct page **pages,
> > +                                         struct vm_area_struct **vmas,
> > +                                         unsigned int gup_flags)
> >  {
> >       unsigned long i;
> >       unsigned long step;
> >       bool drain_allow = true;
> >       bool migrate_allow = true;
> > -     LIST_HEAD(cma_page_list);
> > +     LIST_HEAD(page_list);
> >       long ret = nr_pages;
> >       struct migration_target_control mtc = {
> >               .nid = NUMA_NO_NODE,
> > @@ -1623,13 +1622,12 @@ static long check_and_migrate_cma_pages(struct mm_struct *mm,
> >                */
> >               step = compound_nr(head) - (pages[i] - head);
> >               /*
> > -              * If we get a page from the CMA zone, since we are going to
> > -              * be pinning these entries, we might as well move them out
> > -              * of the CMA zone if possible.
> > +              * If we get a movable page, since we are going to be pinning
> > +              * these entries, try to move them out if possible.
> >                */
> > -             if (is_migrate_cma_page(head)) {
> > +             if (is_migrate_movable(get_pageblock_migratetype(head))) {
>
> is_migrate_movable() isn't a check for the ZONE. It's a check for the
> MIGRATE_TYPE. MIGRATE_TYPE doesn't require hard guarantee for
> migration, and, most of memory, including ZONE_NORMAL, is
> MIGRATE_MOVABLE. With this code, long term gup would always fails due
> to not enough memory. I think that correct change would be
> "is_migrate_cma_page(hear) && zone == ZONE_MOVABLE".

Good point. The above should be OR not AND.

zone_idx(page_zone(head)) == ZONE_MOVABLE || is_migrate_cma_page(hear)

Pasha