[patch 056/262] memcg: unify memcg stat flushing

Andrew Morton
2021-11-05T20:37:38Z

From: Shakeel Butt <shakeelb@google.com>
Subject: memcg: unify memcg stat flushing

The memcg stats can be flushed in multiple context and potentially in
parallel too. For example multiple parallel user space readers for memcg
stats will contend on the rstat locks with each other. There is no need
for that. We just need one flusher and everyone else can benefit. In
addition after aa48e47e3906 ("memcg: infrastructure to flush memcg stats")
the kernel periodically flush the memcg stats from the root, so, the other
flushers will potentially have much less work to do.

Link: https://lkml.kernel.org/r/20211001190040.48086-2-shakeelb@google.com
Signed-off-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: "Michal Koutný" <mkoutny@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

mm/memcontrol.c | 19 ++++++++++---------
1 file changed, 10 insertions(+), 9 deletions(-)

--- a/mm/memcontrol.c~memcg-unify-memcg-stat-flushing
+++ a/mm/memcontrol.c
@@ -660,12 +660,14 @@ static inline void memcg_rstat_updated(s

static void __mem_cgroup_flush_stats(void)
{
- if (!spin_trylock(&stats_flush_lock))
+ unsigned long flag;
+
+ if (!spin_trylock_irqsave(&stats_flush_lock, flag))
return;

cgroup_rstat_flush_irqsafe(root_mem_cgroup->css.cgroup);
atomic_set(&stats_flush_threshold, 0);
- spin_unlock(&stats_flush_lock);
+ spin_unlock_irqrestore(&stats_flush_lock, flag);
}

void mem_cgroup_flush_stats(void)
@@ -1461,7 +1463,7 @@ static char *memory_stat_format(struct m
*
* Current memory state:
*/
- cgroup_rstat_flush(memcg->css.cgroup);
+ mem_cgroup_flush_stats();

for (i = 0; i < ARRAY_SIZE(memory_stats); i++) {
u64 size;
@@ -3565,8 +3567,7 @@ static unsigned long mem_cgroup_usage(st
unsigned long val;

if (mem_cgroup_is_root(memcg)) {
- /* mem_cgroup_threshold() calls here from irqsafe context */
- cgroup_rstat_flush_irqsafe(memcg->css.cgroup);
+ mem_cgroup_flush_stats();
val = memcg_page_state(memcg, NR_FILE_PAGES) +
memcg_page_state(memcg, NR_ANON_MAPPED);
if (swap)
@@ -3947,7 +3948,7 @@ static int memcg_numa_stat_show(struct s
int nid;
struct mem_cgroup *memcg = mem_cgroup_from_seq(m);

- cgroup_rstat_flush(memcg->css.cgroup);
+ mem_cgroup_flush_stats();

for (stat = stats; stat < stats + ARRAY_SIZE(stats); stat++) {
seq_printf(m, "%s=%lu", stat->name,
@@ -4019,7 +4020,7 @@ static int memcg_stat_show(struct seq_fi

BUILD_BUG_ON(ARRAY_SIZE(memcg1_stat_names) != ARRAY_SIZE(memcg1_stats));

- cgroup_rstat_flush(memcg->css.cgroup);
+ mem_cgroup_flush_stats();

for (i = 0; i < ARRAY_SIZE(memcg1_stats); i++) {
unsigned long nr;
@@ -4522,7 +4523,7 @@ void mem_cgroup_wb_stats(struct bdi_writ
struct mem_cgroup *memcg = mem_cgroup_from_css(wb->memcg_css);
struct mem_cgroup *parent;

- cgroup_rstat_flush_irqsafe(memcg->css.cgroup);
+ mem_cgroup_flush_stats();

*pdirty = memcg_page_state(memcg, NR_FILE_DIRTY);
*pwriteback = memcg_page_state(memcg, NR_WRITEBACK);
@@ -6405,7 +6406,7 @@ static int memory_numa_stat_show(struct
int i;
struct mem_cgroup *memcg = mem_cgroup_from_seq(m);

- cgroup_rstat_flush(memcg->css.cgroup);
+ mem_cgroup_flush_stats();

for (i = 0; i < ARRAY_SIZE(memory_stats); i++) {
int nid;
_