[Devel] [PATCH rh7 1/4] memcg: show correct swap max for beancounters

[Vladimir Davydov]

Currently, we assume

  swap.max_held = memory.memsw.max_usage - memory.max_usage

which is obviously wrong. Keep track of maximal swap usage and report it
instead. Note, we don't care about precision and hence don't use any
locking to protect the maximal value, since it doesn't really matter if
max_held will be a couple of pages greater/less than the true value.

Signed-off-by: Vladimir Davydov <vdavydov at parallels.com>
---
 mm/memcontrol.c |   27 +++++++++++++++++++++++----
 1 file changed, 23 insertions(+), 4 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 9dda309b8fae..f164a94ca804 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -278,6 +278,10 @@ struct mem_cgroup {
 	 * the counter to account for kernel memory usage.
 	 */
 	struct res_counter kmem;
+
+	/* beancounter-related stats */
+	unsigned long long swap_max;
+
 	/*
 	 * Should the accounting and control be hierarchical, per subtree?
 	 */
@@ -868,6 +872,18 @@ static void mem_cgroup_swap_statistics(struct mem_cgroup *memcg,
 	this_cpu_add(memcg->stat->count[MEM_CGROUP_STAT_SWAP], val);
 }
 
+static void mem_cgroup_update_swap_max(struct mem_cgroup *memcg)
+{
+	long long swap;
+
+	swap = res_counter_read_u64(&memcg->memsw, RES_USAGE) -
+		res_counter_read_u64(&memcg->res, RES_USAGE);
+
+	/* This is racy, but we don't have to be absolutely precise */
+	if (swap > (long long)memcg->swap_max)
+		memcg->swap_max = swap;
+}
+
 static unsigned long mem_cgroup_read_events(struct mem_cgroup *memcg,
 					    enum mem_cgroup_events_index idx)
 {
@@ -3892,6 +3908,7 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype,
 	memcg_check_events(memcg, page);
 	if (do_swap_account && ctype == MEM_CGROUP_CHARGE_TYPE_SWAPOUT) {
 		mem_cgroup_swap_statistics(memcg, true);
+		mem_cgroup_update_swap_max(memcg);
 		css_get(&memcg->css);
 	}
 	/*
@@ -5137,14 +5154,12 @@ void mem_cgroup_fill_ub_parms(struct cgroup *cg,
 	k->barrier = k->limit = lim;
 
 	s->held	= res_counter_read_u64(&memcg->memsw, RES_USAGE) >> PAGE_SHIFT;
-	s->maxheld = res_counter_read_u64(&memcg->memsw, RES_MAX_USAGE) >> PAGE_SHIFT;
+	s->held -= p->held;
+	s->maxheld = memcg->swap_max >> PAGE_SHIFT;
 	s->failcnt = res_counter_read_u64(&memcg->memsw, RES_FAILCNT);
 	lim = res_counter_read_u64(&memcg->memsw, RES_LIMIT);
 	lim = lim == RESOURCE_MAX ? UB_MAXVALUE :
 		min_t(unsigned long long, lim >> PAGE_SHIFT, UB_MAXVALUE);
-
-	s->held -= p->held;
-	s->maxheld -= p->maxheld;
 	if (lim != UB_MAXVALUE)
 		lim -= p->limit;
 	s->barrier = s->limit = lim;
@@ -6580,6 +6595,10 @@ static void __mem_cgroup_clear_mc(void)
 		/* we've already done css_get(mc.to) */
 		mc.moved_swap = 0;
 	}
+	if (do_swap_account) {
+		mem_cgroup_update_swap_max(from);
+		mem_cgroup_update_swap_max(to);
+	}
 	memcg_oom_recover(from);
 	memcg_oom_recover(to);
 	wake_up_all(&mc.waitq);
-- 
1.7.10.4