Prev: [PATCH 04/14] Allow CONFIG_MIGRATION to be set without CONFIG_NUMA or memory hot-remove
Next: [patch] s390: potential buffer overflow
From: Mel Gorman on 30 Mar 2010 05:20
The fragmentation index may indicate that a failure is due to external
fragmentation but after a compaction run completes, it is still possible
for an allocation to fail. There are two obvious reasons as to why

o Page migration cannot move all pages so fragmentation remains
o A suitable page may exist but watermarks are not met

In the event of compaction followed by an allocation failure, this patch
defers further compaction in the zone for a period of time. The zone that
is deferred is the first zone in the zonelist - i.e. the preferred zone.
To defer compaction in the other zones, the information would need to be
stored in the zonelist or implemented similar to the zonelist_cache.
This would impact the fast-paths and is not justified at this time.

Signed-off-by: Mel Gorman <mel(a)csn.ul.ie>
Acked-by: Rik van Riel <riel(a)redhat.com>
---
include/linux/compaction.h | 35 +++++++++++++++++++++++++++++++++++
include/linux/mmzone.h | 7 +++++++
mm/page_alloc.c | 5 ++++-
3 files changed, 46 insertions(+), 1 deletions(-)

diff --git a/include/linux/compaction.h b/include/linux/compaction.h
index ae98afc..2a02719 100644
--- a/include/linux/compaction.h
+++ b/include/linux/compaction.h
@@ -18,6 +18,32 @@ extern int sysctl_extfrag_handler(struct ctl_table *table, int write,
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);
+
+/* defer_compaction - Do not compact within a zone until a given time */
+static inline void defer_compaction(struct zone *zone, unsigned long resume)
+{
+ /*
+ * This function is called when compaction fails to result in a page
+ * allocation success. This is somewhat unsatisfactory as the failure
+ * to compact has nothing to do with time and everything to do with
+ * the requested order, the number of free pages and watermarks. How
+ * to wait on that is more unclear, but the answer would apply to
+ * other areas where the VM waits based on time.
+ */
+ zone->compact_resume = resume;
+}
+
+static inline int compaction_deferred(struct zone *zone)
+{
+ /* init once if necessary */
+ if (unlikely(!zone->compact_resume)) {
+ zone->compact_resume = jiffies;
+ return 0;
+ }
+
+ return time_before(jiffies, zone->compact_resume);
+}
+
#else
static inline unsigned long try_to_compact_pages(struct zonelist *zonelist,
int order, gfp_t gfp_mask, nodemask_t *nodemask)
@@ -25,6 +51,15 @@ static inline unsigned long try_to_compact_pages(struct zonelist *zonelist,
return COMPACT_INCOMPLETE;
}

+static inline void defer_compaction(struct zone *zone, unsigned long resume)
+{
+}
+
+static inline int compaction_deferred(struct zone *zone)
+{
+ return 1;
+}
+
#endif /* CONFIG_COMPACTION */

#if defined(CONFIG_COMPACTION) && defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index cf9e458..bde879b 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -321,6 +321,13 @@ struct zone {
unsigned long *pageblock_flags;
#endif /* CONFIG_SPARSEMEM */

+#ifdef CONFIG_COMPACTION
+ /*
+ * If a compaction fails, do not try compaction again until
+ * jiffies is after the value of compact_resume
+ */
+ unsigned long compact_resume;
+#endif

ZONE_PADDING(_pad1_)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 7a2e4a2..66823bd 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1770,7 +1770,7 @@ __alloc_pages_direct_reclaim(gfp_t gfp_mask, unsigned int order,
cond_resched();

/* Try memory compaction for high-order allocations before reclaim */
- if (order) {
+ if (order && !compaction_deferred(preferred_zone)) {
*did_some_progress = try_to_compact_pages(zonelist,
order, gfp_mask, nodemask);
if (*did_some_progress != COMPACT_SKIPPED) {
@@ -1795,6 +1795,9 @@ __alloc_pages_direct_reclaim(gfp_t gfp_mask, unsigned int order,
*/
count_vm_event(COMPACTFAIL);

+ /* On failure, avoid compaction for a short time. */
+ defer_compaction(preferred_zone, jiffies + HZ/50);
+
cond_resched();
}
}
--
1.6.5

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo(a)vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
 | 
Pages: 1
Prev: [PATCH 04/14] Allow CONFIG_MIGRATION to be set without CONFIG_NUMA or memory hot-remove
Next: [patch] s390: potential buffer overflow