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

[Minchan Kim]

On Fri, Feb 19, 2010 at 3:02 AM, Mel Gorman <mel@xxxxxxxxx> wrote:
> Ordinarily when a high-order allocation fails, direct reclaim is entered to
> free pages to satisfy the allocation. ÂWith 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@xxxxxxxxx>
> Acked-by: Rik van Riel <riel@xxxxxxxxxx>
> ---
> Âinclude/linux/compaction.h | Â 16 +++++-
> Âinclude/linux/vmstat.h   |  Â1 +
> Âmm/compaction.c      Â| Â118 ++++++++++++++++++++++++++++++++++++++++++++
> Âmm/page_alloc.c      Â|  26 ++++++++++
> Âmm/vmstat.c        Â|  15 +++++-
> Â5 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 @@
> Â#ifndef _LINUX_COMPACTION_H
> Â#define _LINUX_COMPACTION_H
>
> -/* Return values for compact_zone() */
> +/* Return values for compact_zone() and try_to_compact_pages() */
> Â#define COMPACT_INCOMPLETE Â Â 0
> -#define COMPACT_COMPLETE Â Â Â 1
> +#define COMPACT_PARTIAL Â Â Â Â Â Â Â Â1
> +#define COMPACT_COMPLETE Â Â Â 2
>
> Â#ifdef CONFIG_COMPACTION
> Âextern int sysctl_compaction_handler(struct ctl_table *table, int write,
> Â Â Â Â Â Â Â Â Â Â Â Âvoid __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,
> + Â Â Â Â Â Â Â Â Â Â Â int order, gfp_t gfp_mask, nodemask_t *mask);
> +#else
> +static inline unsigned long try_to_compact_pages(struct zonelist *zonelist,
> + Â Â Â Â Â Â Â Â Â Â Â int order, gfp_t gfp_mask, nodemask_t *nodemask)
> +{
> + Â Â Â return COMPACT_INCOMPLETE;
> +}
> +
> Â#endif /* CONFIG_COMPACTION */
>
> Â#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,
> Â Â Â Â Â Â Â ÂKSWAPD_SKIP_CONGESTION_WAIT,
> Â Â Â Â Â Â Â ÂPAGEOUTRUN, ALLOCSTALL, PGROTATED,
> Â Â Â Â Â Â Â ÂCOMPACTBLOCKS, COMPACTPAGES, COMPACTPAGEFAILED,
> + Â Â Â Â Â Â Â COMPACTSTALL, COMPACTFAIL, COMPACTSUCCESS,
> Â#ifdef CONFIG_HUGETLB_PAGE
> Â Â Â Â Â Â Â ÂHTLB_BUDDY_PGALLOC, HTLB_BUDDY_PGALLOC_FAIL,
> Â#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 {
> Â Â Â Âunsigned long nr_anon;
> Â Â Â Âunsigned long nr_file;
>
> + Â Â Â unsigned int order; Â Â Â Â Â Â /* order a direct compactor needs */
> + Â Â Â int migratetype; Â Â Â Â Â Â Â Â/* MOVABLE, RECLAIMABLE etc */
> Â Â Â Âstruct zone *zone;
> Â};
>
> @@ -298,10 +300,31 @@ static void update_nr_listpages(struct compact_control *cc)
> Âstatic inline int compact_finished(struct zone *zone,
> Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Âstruct compact_control *cc)
> Â{
> + Â Â Â unsigned int order;
> + Â Â Â unsigned long watermark = low_wmark_pages(zone) + (1 << cc->order);
> +
> Â Â Â Â/* Compaction run completes if the migrate and free scanner meet */
> Â Â Â Âif (cc->free_pfn <= cc->migrate_pfn)
> Â Â Â Â Â Â Â Âreturn COMPACT_COMPLETE;
>
> + Â Â Â /* Compaction run is not finished if the watermark is not met */
> + Â Â Â if (!zone_watermark_ok(zone, cc->order, watermark, 0, 0))
> + Â Â Â Â Â Â Â return COMPACT_INCOMPLETE;
> +
> + Â Â Â if (cc->order == -1)
> + Â Â Â Â Â Â Â 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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