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Subject[PATCH 1/8] mm: memcontrol: fix cpuhotplug statistics flushing
Date
The memcg hotunplug callback erroneously flushes counts on the local
CPU, not the counts of the CPU going away; those counts will be lost.

Flush the CPU that is actually going away.

Also simplify the code a bit by using mod_memcg_state() and
count_memcg_events() instead of open-coding the upward flush - this is
comparable to how vmstat.c handles hotunplug flushing.

Fixes: a983b5ebee572 ("mm: memcontrol: fix excessive complexity in memory.stat reporting")
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Reviewed-by: Roman Gushchin <guro@fb.com>
Acked-by: Michal Hocko <mhocko@suse.com>
---
mm/memcontrol.c | 35 +++++++++++++++++++++--------------
1 file changed, 21 insertions(+), 14 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index ed5cc78a8dbf..8120d565dd79 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2411,45 +2411,52 @@ static void drain_all_stock(struct mem_cgroup *root_memcg)
static int memcg_hotplug_cpu_dead(unsigned int cpu)
{
struct memcg_stock_pcp *stock;
- struct mem_cgroup *memcg, *mi;
+ struct mem_cgroup *memcg;

stock = &per_cpu(memcg_stock, cpu);
drain_stock(stock);

for_each_mem_cgroup(memcg) {
+ struct memcg_vmstats_percpu *statc;
int i;

+ statc = per_cpu_ptr(memcg->vmstats_percpu, cpu);
+
for (i = 0; i < MEMCG_NR_STAT; i++) {
int nid;
- long x;

- x = this_cpu_xchg(memcg->vmstats_percpu->stat[i], 0);
- if (x)
- for (mi = memcg; mi; mi = parent_mem_cgroup(mi))
- atomic_long_add(x, &memcg->vmstats[i]);
+ if (statc->stat[i]) {
+ mod_memcg_state(memcg, i, statc->stat[i]);
+ statc->stat[i] = 0;
+ }

if (i >= NR_VM_NODE_STAT_ITEMS)
continue;

for_each_node(nid) {
+ struct batched_lruvec_stat *lstatc;
struct mem_cgroup_per_node *pn;
+ long x;

pn = mem_cgroup_nodeinfo(memcg, nid);
- x = this_cpu_xchg(pn->lruvec_stat_cpu->count[i], 0);
- if (x)
+ lstatc = per_cpu_ptr(pn->lruvec_stat_cpu, cpu);
+
+ x = lstatc->count[i];
+ lstatc->count[i] = 0;
+
+ if (x) {
do {
atomic_long_add(x, &pn->lruvec_stat[i]);
} while ((pn = parent_nodeinfo(pn, nid)));
+ }
}
}

for (i = 0; i < NR_VM_EVENT_ITEMS; i++) {
- long x;
-
- x = this_cpu_xchg(memcg->vmstats_percpu->events[i], 0);
- if (x)
- for (mi = memcg; mi; mi = parent_mem_cgroup(mi))
- atomic_long_add(x, &memcg->vmevents[i]);
+ if (statc->events[i]) {
+ count_memcg_events(memcg, i, statc->events[i]);
+ statc->events[i] = 0;
+ }
}
}

--
2.30.0
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