Re: [PATCH 11/12] Direct compact when a high-order allocation fails

[Minchan Kim <minchan.kim@gmail.com>]

On Fri, Feb 19, 2010 at 3:02 AM, 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 6a2eefd..1cf95e2 100644
> --- a/include/linux/compaction.h
> +++ b/include/linux/compaction.h
> @@ -1,13 +1,25 @@
>  #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_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 d7f7236..0ea7a38 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 02579c2..c7c73bb 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;
>  };
>
> @@ -298,10 +300,31 @@ 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;

Where do we set cc->order = -1?
Sorry but I can't find it.


-- 
Kind regards,
Minchan Kim

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