memcg : share event counter rather than duplicate

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

Now logic uses "only increment, no reset" counter and masks for each
checks.  Softlimit chesk was done per 1000 evetns.  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)

ALL event checks are done right after EVENT percpu counter is updated.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memcontrol.c

@@ -63,8 +63,15 @@ static int really_do_swap_account __initdata = 1; /* for remember boot option*/
 #define do_swap_account		(0)
 #endif
 
-#define SOFTLIMIT_EVENTS_THRESH (1000)
-#define THRESHOLDS_EVENTS_THRESH (100)
+/*
+ * Per memcg event counter is incremented at every pagein/pageout. This counter
+ * is used for trigger some periodic events. This is straightforward and better
+ * than using jiffies etc. to handle periodic memcg event.
+ *
+ * These values will be used as !((event) & ((1 <<(thresh)) - 1))
+ */
+#define THRESHOLDS_EVENTS_THRESH (7) /* once in 128 */
+#define SOFTLIMIT_EVENTS_THRESH (10) /* once in 1024 */
 
 /*
  * Statistics for memory cgroup.
@@ -79,10 +86,7 @@ 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 at every  pagein/pageout */
 
 	MEM_CGROUP_STAT_NSTATS,
 };
@@ -154,7 +158,6 @@ struct mem_cgroup_threshold_ary {
 	struct mem_cgroup_threshold entries[0];
 };
 
-static bool mem_cgroup_threshold_check(struct mem_cgroup *mem);
 static void mem_cgroup_threshold(struct mem_cgroup *mem);
 
 /*
@@ -392,19 +395,6 @@ mem_cgroup_remove_exceeded(struct mem_cgroup *mem,
 	spin_unlock(&mctz->lock);
 }
 
-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;
-}
 
 static void mem_cgroup_update_tree(struct mem_cgroup *mem, struct page *page)
 {
@@ -542,8 +532,7 @@ static void mem_cgroup_charge_statistics(struct mem_cgroup *mem,
 		__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_inc(mem->stat->count[MEM_CGROUP_EVENTS]);
 
 	preempt_enable();
 }
@@ -563,6 +552,29 @@ static unsigned long mem_cgroup_get_local_zonestat(struct mem_cgroup *mem,
 	return total;
 }
 
+static bool __memcg_event_check(struct mem_cgroup *mem, int event_mask_shift)
+{
+	s64 val;
+
+	val = this_cpu_read(mem->stat->count[MEM_CGROUP_EVENTS]);
+
+	return !(val & ((1 << event_mask_shift) - 1));
+}
+
+/*
+ * Check events in order.
+ *
+ */
+static void memcg_check_events(struct mem_cgroup *mem, struct page *page)
+{
+	/* threshold event is triggered in finer grain than soft limit */
+	if (unlikely(__memcg_event_check(mem, THRESHOLDS_EVENTS_THRESH))) {
+		mem_cgroup_threshold(mem);
+		if (unlikely(__memcg_event_check(mem, SOFTLIMIT_EVENTS_THRESH)))
+			mem_cgroup_update_tree(mem, page);
+	}
+}
+
 static struct mem_cgroup *mem_cgroup_from_cont(struct cgroup *cont)
 {
 	return container_of(cgroup_subsys_state(cont,
@@ -1686,11 +1698,7 @@ static void __mem_cgroup_commit_charge(struct mem_cgroup *mem,
 	 * Insert ancestor (and ancestor's ancestors), to softlimit RB-tree.
 	 * if they exceeds softlimit.
 	 */
-	if (mem_cgroup_soft_limit_check(mem))
-		mem_cgroup_update_tree(mem, pc->page);
-	if (mem_cgroup_threshold_check(mem))
-		mem_cgroup_threshold(mem);
-
+	memcg_check_events(mem, pc->page);
 }
 
 /**
@@ -1760,6 +1768,11 @@ static int mem_cgroup_move_account(struct page_cgroup *pc,
 		ret = 0;
 	}
 	unlock_page_cgroup(pc);
+	/*
+	 * check events
+	 */
+	memcg_check_events(to, pc->page);
+	memcg_check_events(from, pc->page);
 	return ret;
 }
 
@@ -2128,10 +2141,7 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype)
 	mz = page_cgroup_zoneinfo(pc);
 	unlock_page_cgroup(pc);
 
-	if (mem_cgroup_soft_limit_check(mem))
-		mem_cgroup_update_tree(mem, page);
-	if (mem_cgroup_threshold_check(mem))
-		mem_cgroup_threshold(mem);
+	memcg_check_events(mem, page);
 	/* at swapout, this memcg will be accessed to record to swap */
 	if (ctype != MEM_CGROUP_CHARGE_TYPE_SWAPOUT)
 		css_put(&mem->css);
@@ -3215,20 +3225,6 @@ static int mem_cgroup_swappiness_write(struct cgroup *cgrp, struct cftype *cft,
 	return 0;
 }
 
-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;
-}
-
 static void __mem_cgroup_threshold(struct mem_cgroup *memcg, bool swap)
 {
 	struct mem_cgroup_threshold_ary *t;