mm: move zone->pages_scanned into a vmstat counter
zone->pages_scanned is a write-intensive cache line during page reclaim
and it's also updated during page free. Move the counter into vmstat to
take advantage of the per-cpu updates and do not update it in the free
paths unless necessary.
On a small UMA machine running tiobench the difference is marginal. On
a 4-node machine the overhead is more noticable. Note that automatic
NUMA balancing was disabled for this test as otherwise the system CPU
overhead is unpredictable.
3.16.0-rc3 3.16.0-rc3 3.16.0-rc3
vanillarearrange-v5 vmstat-v5
User 746.94 759.78 774.56
System 65336.22 58350.98 32847.27
Elapsed 27553.52 27282.02 27415.04
Note that the overhead reduction will vary depending on where exactly
pages are allocated and freed.
Signed-off-by: Mel Gorman <mgorman@suse.de>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 8267f77..e574e883 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -763,6 +763,7 @@
"nr_shmem",
"nr_dirtied",
"nr_written",
+ "nr_pages_scanned",
#ifdef CONFIG_NUMA
"numa_hit",
@@ -1067,7 +1068,7 @@
min_wmark_pages(zone),
low_wmark_pages(zone),
high_wmark_pages(zone),
- zone->pages_scanned,
+ zone_page_state(zone, NR_PAGES_SCANNED),
zone->spanned_pages,
zone->present_pages,
zone->managed_pages);