From 508bed884767a8eb394640bae9edcdf082816c43 Mon Sep 17 00:00:00 2001 From: Yosry Ahmed Date: Wed, 29 Nov 2023 03:21:49 +0000 Subject: mm: memcg: change flush_next_time to flush_last_time Patch series "mm: memcg: subtree stats flushing and thresholds", v4. This series attempts to address shortages in today's approach for memcg stats flushing, namely occasionally stale or expensive stat reads. The series does so by changing the threshold that we use to decide whether to trigger a flush to be per memcg instead of global (patch 3), and then changing flushing to be per memcg (i.e. subtree flushes) instead of global (patch 5). This patch (of 5): flush_next_time is an inaccurate name. It's not the next time that periodic flushing will happen, it's rather the next time that ratelimited flushing can happen if the periodic flusher is late. Simplify its semantics by just storing the timestamp of the last flush instead, flush_last_time. Move the 2*FLUSH_TIME addition to mem_cgroup_flush_stats_ratelimited(), and add a comment explaining it. This way, all the ratelimiting semantics live in one place. No functional change intended. Link: https://lkml.kernel.org/r/20231129032154.3710765-1-yosryahmed@google.com Link: https://lkml.kernel.org/r/20231129032154.3710765-2-yosryahmed@google.com Signed-off-by: Yosry Ahmed Tested-by: Domenico Cerasuolo Acked-by: Shakeel Butt Acked-by: Chris Li (Google) Tested-by: Bagas Sanjaya Cc: Greg Thelen Cc: Ivan Babrou Cc: Johannes Weiner Cc: Michal Hocko Cc: Michal Koutny Cc: Muchun Song Cc: Roman Gushchin Cc: Tejun Heo Cc: Waiman Long Cc: Wei Xu Signed-off-by: Andrew Morton --- mm/memcontrol.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) (limited to 'mm/memcontrol.c') diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 69b0ad455242..0dc53e0b5e5c 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -593,7 +593,7 @@ static DECLARE_DEFERRABLE_WORK(stats_flush_dwork, flush_memcg_stats_dwork); static DEFINE_PER_CPU(unsigned int, stats_updates); static atomic_t stats_flush_ongoing = ATOMIC_INIT(0); static atomic_t stats_flush_threshold = ATOMIC_INIT(0); -static u64 flush_next_time; +static u64 flush_last_time; #define FLUSH_TIME (2UL*HZ) @@ -653,7 +653,7 @@ static void do_flush_stats(void) atomic_xchg(&stats_flush_ongoing, 1)) return; - WRITE_ONCE(flush_next_time, jiffies_64 + 2*FLUSH_TIME); + WRITE_ONCE(flush_last_time, jiffies_64); cgroup_rstat_flush(root_mem_cgroup->css.cgroup); @@ -669,7 +669,8 @@ void mem_cgroup_flush_stats(void) void mem_cgroup_flush_stats_ratelimited(void) { - if (time_after64(jiffies_64, READ_ONCE(flush_next_time))) + /* Only flush if the periodic flusher is one full cycle late */ + if (time_after64(jiffies_64, READ_ONCE(flush_last_time) + 2*FLUSH_TIME)) mem_cgroup_flush_stats(); } -- cgit v1.2.3