mm: compaction: direct compact when a high-order allocation fails

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.

[akpm@linux-foundation.org: Fix build errors]
[aarcange@redhat.com: fix count_vm_event preempt in memory compaction direct reclaim]
Signed-off-by: Mel Gorman <mel@csn.ul.ie>
Acked-by: Rik van Riel <riel@redhat.com>
Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Christoph Lameter <cl@linux-foundation.org>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 63 insertions, 0 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index c54376a09f30..cd88a860f088 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -49,6 +49,7 @@
 #include <linux/debugobjects.h>
 #include <linux/kmemleak.h>
 #include <linux/memory.h>
+#include <linux/compaction.h>
 #include <trace/events/kmem.h>
 #include <linux/ftrace_event.h>
 
@@ -1758,6 +1759,59 @@ out:
         return page;
 }
 
+#ifdef CONFIG_COMPACTION
+/* Try memory compaction for high-order allocations before reclaim */
+static struct page *
+__alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
+        struct zonelist *zonelist, enum zone_type high_zoneidx,
+        nodemask_t *nodemask, int alloc_flags, struct zone *preferred_zone,
+        int migratetype, unsigned long *did_some_progress)
+{
+        struct page *page;
+
+        if (!order)
+                return NULL;
+
+        *did_some_progress = try_to_compact_pages(zonelist, order, gfp_mask,
+                                                                nodemask);
+        if (*did_some_progress != COMPACT_SKIPPED) {
+
+                /* Page migration frees to the PCP lists but we want merging */
+                drain_pages(get_cpu());
+                put_cpu();
+
+                page = get_page_from_freelist(gfp_mask, nodemask,
+                                order, zonelist, high_zoneidx,
+                                alloc_flags, preferred_zone,
+                                migratetype);
+                if (page) {
+                        count_vm_event(COMPACTSUCCESS);
+                        return page;
+                }
+
+                /*
+                 * It's bad if compaction run occurs and fails.
+                 * The most likely reason is that pages exist,
+                 * but not enough to satisfy watermarks.
+                 */
+                count_vm_event(COMPACTFAIL);
+
+                cond_resched();
+        }
+
+        return NULL;
+}
+#else
+static inline struct page *
+__alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
+        struct zonelist *zonelist, enum zone_type high_zoneidx,
+        nodemask_t *nodemask, int alloc_flags, struct zone *preferred_zone,
+        int migratetype, unsigned long *did_some_progress)
+{
+        return NULL;
+}
+#endif /* CONFIG_COMPACTION */
+
 /* The really slow allocator path where we enter direct reclaim */
 static inline struct page *
 __alloc_pages_direct_reclaim(gfp_t gfp_mask, unsigned int order,
@@ -1944,6 +1998,15 @@ rebalance:
         if (test_thread_flag(TIF_MEMDIE) && !(gfp_mask & __GFP_NOFAIL))
                 goto nopage;
 
+        /* Try direct compaction */
+        page = __alloc_pages_direct_compact(gfp_mask, order,
+                                        zonelist, high_zoneidx,
+                                        nodemask,
+                                        alloc_flags, preferred_zone,
+                                        migratetype, &did_some_progress);
+        if (page)
+                goto got_pg;
+
         /* Try direct reclaim and then allocating */
         page = __alloc_pages_direct_reclaim(gfp_mask, order,
                                         zonelist, high_zoneidx,