[PATCH 2/2] memcg: share event counter rather than duplicate

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

Memcg has 2 eventcountes which counts "the same" event. Just usages are
different from each other. This patch tries to reduce event counter.

This patch's logic uses "only increment, no reset" new_counter and masks for each
checks. Softlimit chesk was done per 1000 events. So, the similar check
can be done by !(new_counter & 0x3ff). Threshold check was done per 100
events. So, the similar check can be done by (!new_counter & 0x7f)

Cc: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
---
 mm/memcontrol.c |   36 ++++++++++++------------------------
 1 file changed, 12 insertions(+), 24 deletions(-)

Index: mmotm-2.6.33-Feb10/mm/memcontrol.c
===================================================================
--- mmotm-2.6.33-Feb10.orig/mm/memcontrol.c
+++ mmotm-2.6.33-Feb10/mm/memcontrol.c
@@ -63,8 +63,8 @@ static int really_do_swap_account __init
 #define do_swap_account		(0)
 #endif
 
-#define SOFTLIMIT_EVENTS_THRESH (1000)
-#define THRESHOLDS_EVENTS_THRESH (100)
+#define SOFTLIMIT_EVENTS_THRESH (0x3ff) /* once in 1024 */
+#define THRESHOLDS_EVENTS_THRESH (0x7f) /* once in 128 */
 
 /*
  * Statistics for memory cgroup.
@@ -79,10 +79,7 @@ enum mem_cgroup_stat_index {
 	MEM_CGROUP_STAT_PGPGIN_COUNT,	/* # of pages paged in */
 	MEM_CGROUP_STAT_PGPGOUT_COUNT,	/* # of pages paged out */
 	MEM_CGROUP_STAT_SWAPOUT, /* # of pages, swapped out */
-	MEM_CGROUP_STAT_SOFTLIMIT, /* decrements on each page in/out.
-					used by soft limit implementation */
-	MEM_CGROUP_STAT_THRESHOLDS, /* decrements on each page in/out.
-					used by threshold implementation */
+	MEM_CGROUP_EVENTS,	/* incremented by 1 at pagein/pageout */
 
 	MEM_CGROUP_STAT_NSTATS,
 };
@@ -394,16 +391,12 @@ mem_cgroup_remove_exceeded(struct mem_cg
 
 static bool mem_cgroup_soft_limit_check(struct mem_cgroup *mem)
 {
-	bool ret = false;
 	s64 val;
 
-	val = this_cpu_read(mem->stat->count[MEM_CGROUP_STAT_SOFTLIMIT]);
-	if (unlikely(val < 0)) {
-		this_cpu_write(mem->stat->count[MEM_CGROUP_STAT_SOFTLIMIT],
-				SOFTLIMIT_EVENTS_THRESH);
-		ret = true;
-	}
-	return ret;
+	val = this_cpu_read(mem->stat->count[MEM_CGROUP_EVENTS]);
+	if (unlikely(!(val & SOFTLIMIT_EVENTS_THRESH)))
+		return true;
+	return false;
 }
 
 static void mem_cgroup_update_tree(struct mem_cgroup *mem, struct page *page)
@@ -542,8 +535,7 @@ static void mem_cgroup_charge_statistics
 		__this_cpu_inc(mem->stat->count[MEM_CGROUP_STAT_PGPGIN_COUNT]);
 	else
 		__this_cpu_inc(mem->stat->count[MEM_CGROUP_STAT_PGPGOUT_COUNT]);
-	__this_cpu_dec(mem->stat->count[MEM_CGROUP_STAT_SOFTLIMIT]);
-	__this_cpu_dec(mem->stat->count[MEM_CGROUP_STAT_THRESHOLDS]);
+	__this_cpu_dec(mem->stat->count[MEM_CGROUP_EVENTS]);
 
 	preempt_enable();
 }
@@ -3211,16 +3203,12 @@ static int mem_cgroup_swappiness_write(s
 
 static bool mem_cgroup_threshold_check(struct mem_cgroup *mem)
 {
-	bool ret = false;
 	s64 val;
 
-	val = this_cpu_read(mem->stat->count[MEM_CGROUP_STAT_THRESHOLDS]);
-	if (unlikely(val < 0)) {
-		this_cpu_write(mem->stat->count[MEM_CGROUP_STAT_THRESHOLDS],
-				THRESHOLDS_EVENTS_THRESH);
-		ret = true;
-	}
-	return ret;
+	val = this_cpu_read(mem->stat->count[MEM_CGROUP_EVENTS]);
+	if (unlikely(!(val & THRESHOLDS_EVENTS_THRESH)))
+		return true;
+	return false;
 }
 
 static void __mem_cgroup_threshold(struct mem_cgroup *memcg, bool swap)

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