On Fri, Feb 19, 2010 at 11:41:56AM +0900, Minchan Kim wrote:

On Fri, Feb 19, 2010 at 3:02 AM, Mel Gorman [off-list ref] wrote:

quoted

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 <redacted>
Acked-by: Rik van Riel <redacted>
---
 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.

Good spot, it should have been set in compact_node() to force a full
compaction.

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

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