[PATCH openEuler-5.10 12/17] memcg: infrastructure to flush memcg stats

From: Shakeel Butt shakeelb@google.com

mainline inclusion from mainline-v5.15-rc1 commit aa48e47e3906c332eaf1e5d7b58be11d3509ad9f category: feature bugzilla: 185803 https://gitee.com/openeuler/kernel/issues/I4JOG9?from=project-issue CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...

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At the moment memcg stats are read in four contexts:

1. memcg stat user interfaces 2. dirty throttling 3. page fault 4. memory reclaim

Currently the kernel flushes the stats for first two cases. Flushing the stats for remaining two casese may have performance impact. Always flushing the memcg stats on the page fault code path may negatively impacts the performance of the applications. In addition flushing in the memory reclaim code path, though treated as slowpath, can become the source of contention for the global lock taken for stat flushing because when system or memcg is under memory pressure, many tasks may enter the reclaim path.

This patch uses following mechanisms to solve these challenges:

1. Periodically flush the stats from root memcg every 2 seconds. This will time limit the out of sync stats.

2. Asynchronously flush the stats after fixed number of stat updates. In the worst case the stat can be out of sync by O(nr_cpus * BATCH) for 2 seconds.

3. For avoiding thundering herd to flush the stats particularly from the memory reclaim context, introduce memcg local spinlock and let only one flusher active at a time. This could have been done through cgroup_rstat_lock lock but that lock is used by other subsystem and for userspace reading memcg stats. So, it is better to keep flushers introduced by this patch decoupled from cgroup_rstat_lock. However we would have to use irqsafe version of rstat flush but that is fine as this code path will be flushing for whole tree and do the work for everyone. No one will be waiting for that worker.

[shakeelb@google.com: fix sleep-in-wrong context bug] Link: https://lkml.kernel.org/r/20210716212137.1391164-2-shakeelb@google.com

Link: https://lkml.kernel.org/r/20210714013948.270662-2-shakeelb@google.com Signed-off-by: Shakeel Butt shakeelb@google.com Tested-by: Marek Szyprowski m.szyprowski@samsung.com Cc: Hillf Danton hdanton@sina.com Cc: Huang Ying ying.huang@intel.com Cc: Johannes Weiner hannes@cmpxchg.org Cc: Michal Hocko mhocko@kernel.org Cc: Michal Koutný mkoutny@suse.com Cc: Muchun Song songmuchun@bytedance.com Cc: Roman Gushchin guro@fb.com Cc: Tejun Heo tj@kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Conflict: include/linux/memcontrol.h Signed-off-by: Lu Jialin lujialin4@huawei.com Reviewed-by: Kefeng Wang wangkefeng.wang@huawei.com Signed-off-by: Zheng Zengkai zhengzengkai@huawei.com --- include/linux/memcontrol.h | 6 ++++++ mm/memcontrol.c | 34 ++++++++++++++++++++++++++++++++++ mm/vmscan.c | 6 ++++++ 3 files changed, 46 insertions(+)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index fdff0c8f624f..34e4e8de93ce 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -1075,6 +1075,8 @@ static inline unsigned long lruvec_page_state_local(struct lruvec *lruvec, return x; }

+void mem_cgroup_flush_stats(void); + void __mod_memcg_lruvec_state(struct lruvec *lruvec, enum node_stat_item idx, int val); void __mod_lruvec_state(struct lruvec *lruvec, enum node_stat_item idx, @@ -1546,6 +1548,10 @@ static inline unsigned long lruvec_page_state_local(struct lruvec *lruvec, return node_page_state(lruvec_pgdat(lruvec), idx); }

+static inline void mem_cgroup_flush_stats(void) +{ +} + static inline void __mod_memcg_lruvec_state(struct lruvec *lruvec, enum node_stat_item idx, int val) { diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 08e6887fca0d..440ca9225aaa 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -102,6 +102,14 @@ static bool do_memsw_account(void) return !cgroup_subsys_on_dfl(memory_cgrp_subsys) && !cgroup_memory_noswap; }

+/* memcg and lruvec stats flushing */ +static void flush_memcg_stats_dwork(struct work_struct *w); +static DECLARE_DEFERRABLE_WORK(stats_flush_dwork, flush_memcg_stats_dwork); +static void flush_memcg_stats_work(struct work_struct *w); +static DECLARE_WORK(stats_flush_work, flush_memcg_stats_work); +static DEFINE_PER_CPU(unsigned int, stats_flush_threshold); +static DEFINE_SPINLOCK(stats_flush_lock); + #define THRESHOLDS_EVENTS_TARGET 128 #define SOFTLIMIT_EVENTS_TARGET 1024

@@ -691,6 +699,8 @@ 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); + if (!(__this_cpu_inc_return(stats_flush_threshold) % MEMCG_CHARGE_BATCH)) + queue_work(system_unbound_wq, &stats_flush_work); }

/** @@ -5384,6 +5394,10 @@ static int mem_cgroup_css_online(struct cgroup_subsys_state *css) /* Online state pins memcg ID, memcg ID pins CSS */ refcount_set(&memcg->id.ref, 1); css_get(css); + + if (unlikely(mem_cgroup_is_root(memcg))) + queue_delayed_work(system_unbound_wq, &stats_flush_dwork, + 2UL*HZ); return 0; }

@@ -5475,6 +5489,26 @@ static void mem_cgroup_css_reset(struct cgroup_subsys_state *css) memcg_wb_domain_size_changed(memcg); }

+void mem_cgroup_flush_stats(void) +{ + if (!spin_trylock(&stats_flush_lock)) + return; + + cgroup_rstat_flush_irqsafe(root_mem_cgroup->css.cgroup); + spin_unlock(&stats_flush_lock); +} + +static void flush_memcg_stats_dwork(struct work_struct *w) +{ + mem_cgroup_flush_stats(); + queue_delayed_work(system_unbound_wq, &stats_flush_dwork, 2UL*HZ); +} + +static void flush_memcg_stats_work(struct work_struct *w) +{ + mem_cgroup_flush_stats(); +} + static void mem_cgroup_css_rstat_flush(struct cgroup_subsys_state *css, int cpu) { struct mem_cgroup *memcg = mem_cgroup_from_css(css); diff --git a/mm/vmscan.c b/mm/vmscan.c index 732356256b26..c851e5f91842 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -2903,6 +2903,12 @@ static void shrink_node(pg_data_t *pgdat, struct scan_control *sc) target_lruvec = mem_cgroup_lruvec(sc->target_mem_cgroup, pgdat);

again: + /* + * Flush the memory cgroup stats, so that we read accurate per-memcg + * lruvec stats for heuristics. + */ + mem_cgroup_flush_stats(); + memset(&sc->nr, 0, sizeof(sc->nr));

nr_reclaimed = sc->nr_reclaimed;