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    SubjectRe: [PATCH 10/11] Direct compact when a high-order allocation fails
    On Wed, Mar 24, 2010 at 09:06:51PM +0900, Minchan Kim wrote:
    > On Wed, Mar 24, 2010 at 8:59 PM, Minchan Kim <minchan.kim@gmail.com> wrote:
    > > On Wed, Mar 24, 2010 at 8:11 PM, Mel Gorman <mel@csn.ul.ie> wrote:
    > >> On Wed, Mar 24, 2010 at 08:10:40AM +0900, Minchan Kim wrote:
    > >>> Hi, Mel.
    > >>>
    > >>> On Tue, Mar 23, 2010 at 9:25 PM, Mel Gorman <mel@csn.ul.ie> wrote:
    > >>> > Ordinarily when a high-order allocation fails, direct reclaim is entered to
    > >>> > free pages to satisfy the allocation.  With this patch, it is determined if
    > >>> > an allocation failed due to external fragmentation instead of low memory
    > >>> > and if so, the calling process will compact until a suitable page is
    > >>> > freed. Compaction by moving pages in memory is considerably cheaper than
    > >>> > paging out to disk and works where there are locked pages or no swap. If
    > >>> > compaction fails to free a page of a suitable size, then reclaim will
    > >>> > still occur.
    > >>> >
    > >>> > Direct compaction returns as soon as possible. As each block is compacted,
    > >>> > it is checked if a suitable page has been freed and if so, it returns.
    > >>> >
    > >>> > Signed-off-by: Mel Gorman <mel@csn.ul.ie>
    > >>> > Acked-by: Rik van Riel <riel@redhat.com>
    > >>> > ---
    > >>> >  include/linux/compaction.h |   16 +++++-
    > >>> >  include/linux/vmstat.h     |    1 +
    > >>> >  mm/compaction.c            |  118 ++++++++++++++++++++++++++++++++++++++++++++
    > >>> >  mm/page_alloc.c            |   26 ++++++++++
    > >>> >  mm/vmstat.c                |   15 +++++-
    > >>> >  5 files changed, 172 insertions(+), 4 deletions(-)
    > >>> >
    > >>> > diff --git a/include/linux/compaction.h b/include/linux/compaction.h
    > >>> > index c94890b..b851428 100644
    > >>> > --- a/include/linux/compaction.h
    > >>> > +++ b/include/linux/compaction.h
    > >>> > @@ -1,14 +1,26 @@
    > >>> >  #ifndef _LINUX_COMPACTION_H
    > >>> >  #define _LINUX_COMPACTION_H
    > >>> >
    > >>> > -/* Return values for compact_zone() */
    > >>> > +/* Return values for compact_zone() and try_to_compact_pages() */
    > >>> >  #define COMPACT_INCOMPLETE     0
    > >>> > -#define COMPACT_COMPLETE       1
    > >>> > +#define COMPACT_PARTIAL                1
    > >>> > +#define COMPACT_COMPLETE       2
    > >>> >
    > >>> >  #ifdef CONFIG_COMPACTION
    > >>> >  extern int sysctl_compact_memory;
    > >>> >  extern int sysctl_compaction_handler(struct ctl_table *table, int write,
    > >>> >                        void __user *buffer, size_t *length, loff_t *ppos);
    > >>> > +
    > >>> > +extern int fragmentation_index(struct zone *zone, unsigned int order);
    > >>> > +extern unsigned long try_to_compact_pages(struct zonelist *zonelist,
    > >>> > +                       int order, gfp_t gfp_mask, nodemask_t *mask);
    > >>> > +#else
    > >>> > +static inline unsigned long try_to_compact_pages(struct zonelist *zonelist,
    > >>> > +                       int order, gfp_t gfp_mask, nodemask_t *nodemask)
    > >>> > +{
    > >>> > +       return COMPACT_INCOMPLETE;
    > >>> > +}
    > >>> > +
    > >>> >  #endif /* CONFIG_COMPACTION */
    > >>> >
    > >>> >  #if defined(CONFIG_COMPACTION) && defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
    > >>> > diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
    > >>> > index 56e4b44..b4b4d34 100644
    > >>> > --- a/include/linux/vmstat.h
    > >>> > +++ b/include/linux/vmstat.h
    > >>> > @@ -44,6 +44,7 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
    > >>> >                KSWAPD_SKIP_CONGESTION_WAIT,
    > >>> >                PAGEOUTRUN, ALLOCSTALL, PGROTATED,
    > >>> >                COMPACTBLOCKS, COMPACTPAGES, COMPACTPAGEFAILED,
    > >>> > +               COMPACTSTALL, COMPACTFAIL, COMPACTSUCCESS,
    > >>> >  #ifdef CONFIG_HUGETLB_PAGE
    > >>> >                HTLB_BUDDY_PGALLOC, HTLB_BUDDY_PGALLOC_FAIL,
    > >>> >  #endif
    > >>> > diff --git a/mm/compaction.c b/mm/compaction.c
    > >>> > index 8df6e3d..6688700 100644
    > >>> > --- a/mm/compaction.c
    > >>> > +++ b/mm/compaction.c
    > >>> > @@ -34,6 +34,8 @@ struct compact_control {
    > >>> >        unsigned long nr_anon;
    > >>> >        unsigned long nr_file;
    > >>> >
    > >>> > +       unsigned int order;             /* order a direct compactor needs */
    > >>> > +       int migratetype;                /* MOVABLE, RECLAIMABLE etc */
    > >>> >        struct zone *zone;
    > >>> >  };
    > >>> >
    > >>> > @@ -301,10 +303,31 @@ static void update_nr_listpages(struct compact_control *cc)
    > >>> >  static inline int compact_finished(struct zone *zone,
    > >>> >                                                struct compact_control *cc)
    > >>> >  {
    > >>> > +       unsigned int order;
    > >>> > +       unsigned long watermark = low_wmark_pages(zone) + (1 << cc->order);
    > >>> > +
    > >>> >        /* Compaction run completes if the migrate and free scanner meet */
    > >>> >        if (cc->free_pfn <= cc->migrate_pfn)
    > >>> >                return COMPACT_COMPLETE;
    > >>> >
    > >>> > +       /* Compaction run is not finished if the watermark is not met */
    > >>> > +       if (!zone_watermark_ok(zone, cc->order, watermark, 0, 0))
    > >>> > +               return COMPACT_INCOMPLETE;
    > >>> > +
    > >>> > +       if (cc->order == -1)
    > >>> > +               return COMPACT_INCOMPLETE;
    > >>> > +
    > >>> > +       /* Direct compactor: Is a suitable page free? */
    > >>> > +       for (order = cc->order; order < MAX_ORDER; order++) {
    > >>> > +               /* Job done if page is free of the right migratetype */
    > >>> > +               if (!list_empty(&zone->free_area[order].free_list[cc->migratetype]))
    > >>> > +                       return COMPACT_PARTIAL;
    > >>> > +
    > >>> > +               /* Job done if allocation would set block type */
    > >>> > +               if (order >= pageblock_order && zone->free_area[order].nr_free)
    > >>> > +                       return COMPACT_PARTIAL;
    > >>> > +       }
    > >>> > +
    > >>> >        return COMPACT_INCOMPLETE;
    > >>> >  }
    > >>> >
    > >>> > @@ -348,6 +371,101 @@ static int compact_zone(struct zone *zone, struct compact_control *cc)
    > >>> >        return ret;
    > >>> >  }
    > >>> >
    > >>> > +static inline unsigned long compact_zone_order(struct zone *zone,
    > >>> > +                                               int order, gfp_t gfp_mask)
    > >>> > +{
    > >>> > +       struct compact_control cc = {
    > >>> > +               .nr_freepages = 0,
    > >>> > +               .nr_migratepages = 0,
    > >>> > +               .order = order,
    > >>> > +               .migratetype = allocflags_to_migratetype(gfp_mask),
    > >>> > +               .zone = zone,
    > >>> > +       };
    > >>> > +       INIT_LIST_HEAD(&cc.freepages);
    > >>> > +       INIT_LIST_HEAD(&cc.migratepages);
    > >>> > +
    > >>> > +       return compact_zone(zone, &cc);
    > >>> > +}
    > >>> > +
    > >>> > +/**
    > >>> > + * try_to_compact_pages - Direct compact to satisfy a high-order allocation
    > >>> > + * @zonelist: The zonelist used for the current allocation
    > >>> > + * @order: The order of the current allocation
    > >>> > + * @gfp_mask: The GFP mask of the current allocation
    > >>> > + * @nodemask: The allowed nodes to allocate from
    > >>> > + *
    > >>> > + * This is the main entry point for direct page compaction.
    > >>> > + */
    > >>> > +unsigned long try_to_compact_pages(struct zonelist *zonelist,
    > >>> > +                       int order, gfp_t gfp_mask, nodemask_t *nodemask)
    > >>> > +{
    > >>> > +       enum zone_type high_zoneidx = gfp_zone(gfp_mask);
    > >>> > +       int may_enter_fs = gfp_mask & __GFP_FS;
    > >>> > +       int may_perform_io = gfp_mask & __GFP_IO;
    > >>> > +       unsigned long watermark;
    > >>> > +       struct zoneref *z;
    > >>> > +       struct zone *zone;
    > >>> > +       int rc = COMPACT_INCOMPLETE;
    > >>> > +
    > >>> > +       /* Check whether it is worth even starting compaction */
    > >>> > +       if (order == 0 || !may_enter_fs || !may_perform_io)
    > >>> > +               return rc;
    > >>> > +
    > >>> > +       /*
    > >>> > +        * We will not stall if the necessary conditions are not met for
    > >>> > +        * migration but direct reclaim seems to account stalls similarly
    > >>> > +        */
    >
    > Then, Let's remove this comment.
    >

    Yes, it hinders more than it helps in this case. It's deleted now.

    --
    Mel Gorman
    Part-time Phd Student Linux Technology Center
    University of Limerick IBM Dublin Software Lab
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