[patch 3/7] mm, memcg: partially revert "mm/memcontrol.c: keep local VM counters in sync with the hierarchical ones"

[patch 3/7] mm, memcg: partially revert "mm/memcontrol.c: keep local VM counters in sync with the hierarchical ones"

[akpm]

From: Roman Gushchin <guro@fb.com>
Subject: mm, memcg: partially revert "mm/memcontrol.c: keep local VM counters in sync with the hierarchical ones"

Commit 766a4c19d880 ("mm/memcontrol.c: keep local VM counters in sync with
the hierarchical ones") effectively decreased the precision of per-memcg
vmstats_local and per-memcg-per-node lruvec percpu counters.

That's good for displaying in memory.stat, but brings a serious regression
into the reclaim process.

One issue I've discovered and debugged is the following: lruvec_lru_size()
can return 0 instead of the actual number of pages in the lru list,
preventing the kernel to reclaim last remaining pages.  Result is yet
another dying memory cgroups flooding.  The opposite is also happening:
scanning an empty lru list is the waste of cpu time.

Also, inactive_list_is_low() can return incorrect values, preventing the
active lru from being scanned and freed.  It can fail both because the
size of active and inactive lists are inaccurate, and because the number
of workingset refaults isn't precise.  In other words, the result is
pretty random.

I'm not sure, if using the approximate number of slab pages in
count_shadow_number() is acceptable, but issues described above are enough
to partially revert the patch.

Let's keep per-memcg vmstat_local batched (they are only used for
displaying stats to the userspace), but keep lruvec stats precise.  This
change fixes the dead memcg flooding on my setup.

Link: http://lkml.kernel.org/r/20190817004726.2530670-1-guro@fb.com
Fixes: 766a4c19d880 ("mm/memcontrol.c: keep local VM counters in sync with the hierarchical ones")
Signed-off-by: Roman Gushchin <guro@fb.com>
Acked-by: Yafang Shao <laoar.shao@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/memcontrol.c |    8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

--- a/mm/memcontrol.c~partially-revert-mm-memcontrolc-keep-local-vm-counters-in-sync-with-the-hierarchical-ones
+++ a/mm/memcontrol.c
@@ -752,15 +752,13 @@ void __mod_lruvec_state(struct lruvec *l
 	/* Update memcg */
 	__mod_memcg_state(memcg, idx, val);
 
+	/* Update lruvec */
+	__this_cpu_add(pn->lruvec_stat_local->count[idx], val);
+
 	x = val + __this_cpu_read(pn->lruvec_stat_cpu->count[idx]);
 	if (unlikely(abs(x) > MEMCG_CHARGE_BATCH)) {
 		struct mem_cgroup_per_node *pi;
 
-		/*
-		 * Batch local counters to keep them in sync with
-		 * the hierarchical ones.
-		 */
-		__this_cpu_add(pn->lruvec_stat_local->count[idx], x);
 		for (pi = pn; pi; pi = parent_nodeinfo(pi, pgdat->node_id))
 			atomic_long_add(x, &pi->lruvec_stat[idx]);
 		x = 0;
_