[RFC PATCH v4 39/40] mm: Add intelligence in kmempowerd to ignore regions unsuitable for evacuation

["Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>]

Enhance kmempowerd to determine situations where evacuating a region would prove
to be too costly or counter-productive, and ignore those regions for region
evacuation.

For example, if the region has a significant number of used pages (say more than
32), then evacuation will involve more work and might not be justifiable. Also,
compacting region 0 would be pointless, since that is the target of all our
compaction runs. Add these checks in the region-evacuator.

Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
---

 include/linux/mmzone.h |    2 ++
 mm/compaction.c        |   25 +++++++++++++++++++++++--
 mm/internal.h          |    2 ++
 3 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 257afdf..f383cc8d4 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -84,6 +84,8 @@ static inline int get_pageblock_migratetype(struct page *page)
 	return get_pageblock_flags_group(page, PB_migrate, PB_migrate_end);
 }
 
+#define MAX_MEMPWR_MIGRATE_PAGES	32
+
 struct mem_region_list {
 	struct list_head	*page_block;
 	unsigned long		nr_free;
diff --git a/mm/compaction.c b/mm/compaction.c
index b56be89..41585b0 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1297,9 +1297,26 @@ void queue_mempower_work(struct pglist_data *pgdat, struct zone *zone,
 	queue_kthread_work(&pgdat->mempower_worker, &mpwork->work);
 }
 
+int should_evacuate_region(struct zone *z, struct zone_mem_region *region)
+{
+	unsigned long pages_in_use;
+
+	/* Don't try to evacuate region 0, since its the target of migration */
+	if (region == z->zone_regions)
+		return 0;
+
+	pages_in_use = region->present_pages - region->nr_free;
+
+	if (pages_in_use > 0 && pages_in_use <= MAX_MEMPWR_MIGRATE_PAGES)
+		return 1;
+
+	return 0;
+}
+
 static void kmempowerd(struct kthread_work *work)
 {
 	struct mempower_work *mpwork;
+	struct zone_mem_region *zmr;
 	struct zone *zone;
 	unsigned long flags;
 	int region_id;
@@ -1315,8 +1332,12 @@ repeat:
 	if (bitmap_empty(mpwork_mask, nr_zone_region_bits))
 		return;
 
-	for_each_set_bit(region_id, mpwork_mask, nr_zone_region_bits)
-		evacuate_mem_region(zone, &zone->zone_regions[region_id]);
+	for_each_set_bit(region_id, mpwork_mask, nr_zone_region_bits) {
+		zmr = &zone->zone_regions[region_id];
+
+		if (should_evacuate_region(zone, zmr))
+			evacuate_mem_region(zone, zmr);
+	}
 
 	spin_lock_irqsave(&mpwork->lock, flags);
 
diff --git a/mm/internal.h b/mm/internal.h
index 3fbc9f6..5b4658c 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -184,6 +184,8 @@ int compact_range(struct compact_control *cc, struct aggression_control *ac,
 void queue_mempower_work(struct pglist_data *pgdat, struct zone *zone,
 			 int region_id);
 
+int should_evacuate_region(struct zone *z, struct zone_mem_region *region);
+
 #endif
 
 /*

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