Help Resource Counters Scale better (v4)

[Balbir Singh <balbir@linux.vnet.ibm.com>]

Enhancement: Remove the overhead of root based resource counter accounting

From: Balbir Singh <balbir@linux.vnet.ibm.com>

This patch reduces the resource counter overhead (mostly spinlock)
associated with the root cgroup. This is a part of the several
patches to reduce mem cgroup overhead. I had posted other
approaches earlier (including using percpu counters). Those
patches will be a natural addition and will be added iteratively
on top of these.

The patch stops resource counter accounting for the root cgroup.
The data for display is derived from the statisitcs we maintain
via mem_cgroup_charge_statistics (which is more scalable).

The tests results I see on a 24 way show that

1. The lock contention disappears from /proc/lock_stats
2. The results of the test are comparable to running with
   cgroup_disable=memory.

Please test/review.

---

 mm/memcontrol.c |   89 +++++++++++++++++++++++++++++++++++++++++++------------
 1 files changed, 70 insertions(+), 19 deletions(-)


diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 48a38e1..6d82f8d 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -70,6 +70,7 @@ 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_EVENTS,	/* sum of pagein + pageout for internal use */
+	MEM_CGROUP_STAT_SWAPOUT, /* # of pages, swapped out */
 
 	MEM_CGROUP_STAT_NSTATS,
 };
@@ -478,6 +479,19 @@ mem_cgroup_largest_soft_limit_node(struct mem_cgroup_tree_per_zone *mctz)
 	return mz;
 }
 
+static void mem_cgroup_swap_statistics(struct mem_cgroup *mem,
+					 bool charge)
+{
+	int val = (charge)? 1 : -1;
+	struct mem_cgroup_stat *stat = &mem->stat;
+	struct mem_cgroup_stat_cpu *cpustat;
+	int cpu = get_cpu();
+
+	cpustat = &stat->cpustat[cpu];
+	__mem_cgroup_stat_add_safe(cpustat, MEM_CGROUP_STAT_SWAPOUT, val);
+	put_cpu();
+}
+
 static void mem_cgroup_charge_statistics(struct mem_cgroup *mem,
 					 struct page_cgroup *pc,
 					 bool charge)
@@ -1281,9 +1295,11 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm,
 	VM_BUG_ON(css_is_removed(&mem->css));
 
 	while (1) {
-		int ret;
+		int ret = 0;
 		unsigned long flags = 0;
 
+		if (mem_cgroup_is_root(mem))
+			goto done;
 		ret = res_counter_charge(&mem->res, PAGE_SIZE, &fail_res,
 						&soft_fail_res);
 		if (likely(!ret)) {
@@ -1343,6 +1359,7 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm,
 		if (mem_cgroup_soft_limit_check(mem_over_soft_limit))
 			mem_cgroup_update_tree(mem_over_soft_limit, page);
 	}
+done:
 	return 0;
 nomem:
 	css_put(&mem->css);
@@ -1415,9 +1432,12 @@ static void __mem_cgroup_commit_charge(struct mem_cgroup *mem,
 	lock_page_cgroup(pc);
 	if (unlikely(PageCgroupUsed(pc))) {
 		unlock_page_cgroup(pc);
-		res_counter_uncharge(&mem->res, PAGE_SIZE, NULL);
-		if (do_swap_account)
-			res_counter_uncharge(&mem->memsw, PAGE_SIZE, NULL);
+		if (!mem_cgroup_is_root(mem)) {
+			res_counter_uncharge(&mem->res, PAGE_SIZE, NULL);
+			if (do_swap_account)
+				res_counter_uncharge(&mem->memsw, PAGE_SIZE,
+							NULL);
+		}
 		css_put(&mem->css);
 		return;
 	}
@@ -1494,7 +1514,8 @@ static int mem_cgroup_move_account(struct page_cgroup *pc,
 	if (pc->mem_cgroup != from)
 		goto out;
 
-	res_counter_uncharge(&from->res, PAGE_SIZE, NULL);
+	if (!mem_cgroup_is_root(from))
+		res_counter_uncharge(&from->res, PAGE_SIZE, NULL);
 	mem_cgroup_charge_statistics(from, pc, false);
 
 	page = pc->page;
@@ -1513,7 +1534,7 @@ static int mem_cgroup_move_account(struct page_cgroup *pc,
 						1);
 	}
 
-	if (do_swap_account)
+	if (do_swap_account && !mem_cgroup_is_root(from))
 		res_counter_uncharge(&from->memsw, PAGE_SIZE, NULL);
 	css_put(&from->css);
 
@@ -1584,9 +1605,11 @@ uncharge:
 	/* drop extra refcnt by try_charge() */
 	css_put(&parent->css);
 	/* uncharge if move fails */
-	res_counter_uncharge(&parent->res, PAGE_SIZE, NULL);
-	if (do_swap_account)
-		res_counter_uncharge(&parent->memsw, PAGE_SIZE, NULL);
+	if (!mem_cgroup_is_root(parent)) {
+		res_counter_uncharge(&parent->res, PAGE_SIZE, NULL);
+		if (do_swap_account)
+			res_counter_uncharge(&parent->memsw, PAGE_SIZE, NULL);
+	}
 	return ret;
 }
 
@@ -1775,7 +1798,10 @@ __mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr,
 			 * This recorded memcg can be obsolete one. So, avoid
 			 * calling css_tryget
 			 */
-			res_counter_uncharge(&memcg->memsw, PAGE_SIZE, NULL);
+			if (!mem_cgroup_is_root(memcg))
+				res_counter_uncharge(&memcg->memsw, PAGE_SIZE,
+							NULL);
+			mem_cgroup_swap_statistics(memcg, false);
 			mem_cgroup_put(memcg);
 		}
 		rcu_read_unlock();
@@ -1800,9 +1826,11 @@ void mem_cgroup_cancel_charge_swapin(struct mem_cgroup *mem)
 		return;
 	if (!mem)
 		return;
-	res_counter_uncharge(&mem->res, PAGE_SIZE, NULL);
-	if (do_swap_account)
-		res_counter_uncharge(&mem->memsw, PAGE_SIZE, NULL);
+	if (!mem_cgroup_is_root(mem)) {
+		res_counter_uncharge(&mem->res, PAGE_SIZE, NULL);
+		if (do_swap_account)
+			res_counter_uncharge(&mem->memsw, PAGE_SIZE, NULL);
+	}
 	css_put(&mem->css);
 }
 
@@ -1855,9 +1883,14 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype)
 		break;
 	}
 
-	res_counter_uncharge(&mem->res, PAGE_SIZE, &soft_limit_excess);
-	if (do_swap_account && (ctype != MEM_CGROUP_CHARGE_TYPE_SWAPOUT))
-		res_counter_uncharge(&mem->memsw, PAGE_SIZE, NULL);
+	if (!mem_cgroup_is_root(mem)) {
+		res_counter_uncharge(&mem->res, PAGE_SIZE, &soft_limit_excess);
+		if (do_swap_account &&
+				(ctype != MEM_CGROUP_CHARGE_TYPE_SWAPOUT))
+			res_counter_uncharge(&mem->memsw, PAGE_SIZE, NULL);
+	}
+	if (ctype == MEM_CGROUP_CHARGE_TYPE_SWAPOUT && mem_cgroup_is_root(mem))
+		mem_cgroup_swap_statistics(mem, true);
 	mem_cgroup_charge_statistics(mem, pc, false);
 
 	ClearPageCgroupUsed(pc);
@@ -1948,7 +1981,9 @@ void mem_cgroup_uncharge_swap(swp_entry_t ent)
 		 * We uncharge this because swap is freed.
 		 * This memcg can be obsolete one. We avoid calling css_tryget
 		 */
-		res_counter_uncharge(&memcg->memsw, PAGE_SIZE, NULL);
+		if (!mem_cgroup_is_root(memcg))
+			res_counter_uncharge(&memcg->memsw, PAGE_SIZE, NULL);
+		mem_cgroup_swap_statistics(memcg, false);
 		mem_cgroup_put(memcg);
 	}
 	rcu_read_unlock();
@@ -2461,10 +2496,26 @@ static u64 mem_cgroup_read(struct cgroup *cont, struct cftype *cft)
 	name = MEMFILE_ATTR(cft->private);
 	switch (type) {
 	case _MEM:
-		val = res_counter_read_u64(&mem->res, name);
+		if (name == RES_USAGE && mem_cgroup_is_root(mem)) {
+			val = mem_cgroup_read_stat(&mem->stat,
+					MEM_CGROUP_STAT_CACHE);
+			val += mem_cgroup_read_stat(&mem->stat,
+					MEM_CGROUP_STAT_RSS);
+			val <<= PAGE_SHIFT;
+		} else
+			val = res_counter_read_u64(&mem->res, name);
 		break;
 	case _MEMSWAP:
-		val = res_counter_read_u64(&mem->memsw, name);
+		if (name == RES_USAGE && mem_cgroup_is_root(mem)) {
+			val = mem_cgroup_read_stat(&mem->stat,
+					MEM_CGROUP_STAT_CACHE);
+			val += mem_cgroup_read_stat(&mem->stat,
+					MEM_CGROUP_STAT_RSS);
+			val += mem_cgroup_read_stat(&mem->stat,
+					MEM_CGROUP_STAT_SWAPOUT);
+			val <<= PAGE_SHIFT;
+		} else
+			val = res_counter_read_u64(&mem->memsw, name);
 		break;
 	default:
 		BUG();

-- 
	Balbir

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