From: Shakeel Butt shakeelb@google.com
commit 5b3be698a872c490dbed524f3e2463701ab21339 upstream.
Commit 11192d9c124d ("memcg: flush stats only if updated") added tracking of memcg stats updates which is used by the readers to flush only if the updates are over a certain threshold. However each individual update can correspond to a large value change for a given stat. For example adding or removing a hugepage to an LRU changes the stat by thp_nr_pages (512 on x86_64).
Treating the update related to THP as one can keep the stat off, in theory, by (thp_nr_pages * nr_cpus * CHARGE_BATCH) before flush.
To handle such scenarios, this patch adds consideration of the stat update value as well instead of just the update event. In addition let the asyn flusher unconditionally flush the stats to put time limit on the stats skew and hopefully a lot less readers would need to flush.
Link: https://lkml.kernel.org/r/20211118065350.697046-1-shakeelb@google.com Signed-off-by: Shakeel Butt shakeelb@google.com Cc: 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 Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Cc: Ivan Babrou ivan@cloudflare.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- mm/memcontrol.c | 20 +++++++++++++------- 1 file changed, 13 insertions(+), 7 deletions(-)
--- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -629,11 +629,17 @@ static DEFINE_SPINLOCK(stats_flush_lock) static DEFINE_PER_CPU(unsigned int, stats_updates); static atomic_t stats_flush_threshold = ATOMIC_INIT(0);
-static inline void memcg_rstat_updated(struct mem_cgroup *memcg) +static inline void memcg_rstat_updated(struct mem_cgroup *memcg, int val) { + unsigned int x; + cgroup_rstat_updated(memcg->css.cgroup, smp_processor_id()); - if (!(__this_cpu_inc_return(stats_updates) % MEMCG_CHARGE_BATCH)) - atomic_inc(&stats_flush_threshold); + + x = __this_cpu_add_return(stats_updates, abs(val)); + if (x > MEMCG_CHARGE_BATCH) { + atomic_add(x / MEMCG_CHARGE_BATCH, &stats_flush_threshold); + __this_cpu_write(stats_updates, 0); + } }
static void __mem_cgroup_flush_stats(void) @@ -656,7 +662,7 @@ void mem_cgroup_flush_stats(void)
static void flush_memcg_stats_dwork(struct work_struct *w) { - mem_cgroup_flush_stats(); + __mem_cgroup_flush_stats(); queue_delayed_work(system_unbound_wq, &stats_flush_dwork, 2UL*HZ); }
@@ -672,7 +678,7 @@ void __mod_memcg_state(struct mem_cgroup return;
__this_cpu_add(memcg->vmstats_percpu->state[idx], val); - memcg_rstat_updated(memcg); + memcg_rstat_updated(memcg, val); }
/* idx can be of type enum memcg_stat_item or node_stat_item. */ @@ -705,7 +711,7 @@ void __mod_memcg_lruvec_state(struct lru /* Update lruvec */ __this_cpu_add(pn->lruvec_stats_percpu->state[idx], val);
- memcg_rstat_updated(memcg); + memcg_rstat_updated(memcg, val); }
/** @@ -789,7 +795,7 @@ void __count_memcg_events(struct mem_cgr return;
__this_cpu_add(memcg->vmstats_percpu->events[idx], count); - memcg_rstat_updated(memcg); + memcg_rstat_updated(memcg, count); }
static unsigned long memcg_events(struct mem_cgroup *memcg, int event)