From 6ebe994b54a63f78e7bba65ac5ebaca7dfa88526 Mon Sep 17 00:00:00 2001 From: Shakeel Butt Date: Fri, 14 Jan 2022 14:05:39 -0800 Subject: [PATCH] memcg: better bounds on the memcg stats updates MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit 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 Cc: Johannes Weiner Cc: Michal Hocko Cc: "Michal Koutný" Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Cc: Ivan Babrou Signed-off-by: Greg Kroah-Hartman --- mm/memcontrol.c | 20 +++++++++++++------- 1 file changed, 13 insertions(+), 7 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index b174c0c..96cd7ea 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -651,11 +651,17 @@ 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) @@ -678,7 +684,7 @@ 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); } @@ -694,7 +700,7 @@ void __mod_memcg_state(struct mem_cgroup *memcg, int idx, int val) 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. */ @@ -727,7 +733,7 @@ void __mod_memcg_lruvec_state(struct lruvec *lruvec, enum node_stat_item idx, /* Update lruvec */ __this_cpu_add(pn->lruvec_stats_percpu->state[idx], val); - memcg_rstat_updated(memcg); + memcg_rstat_updated(memcg, val); } /** @@ -829,7 +835,7 @@ void __count_memcg_events(struct mem_cgroup *memcg, enum vm_event_item idx, 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) -- 2.7.4