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UPSTREAM: mm: memcg: change flush_next_time to flush_last_time

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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
Change-Id: Ic4ba631a402542acb2413ad212ef5839fed03509
Signed-off-by: Yosry Ahmed <yosryahmed@google.com>
Tested-by: Domenico Cerasuolo <cerasuolodomenico@gmail.com>
Acked-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Chris Li <chrisl@kernel.org> (Google)
Tested-by: Bagas Sanjaya <bagasdotme@gmail.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: Ivan Babrou <ivan@cloudflare.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Michal Koutny <mkoutny@suse.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Tejun Heo <tj@kernel.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Wei Xu <weixugc@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
(cherry picked from commit 508bed8847)
Bug: 322544714
Signed-off-by: T.J. Mercier <tjmercier@google.com>
This commit is contained in:
Yosry Ahmed 2023-11-29 03:21:49 +00:00 committed by Carlos Llamas
parent a38b207d4f
commit 01d12c8b2c
1 changed files with 4 additions and 3 deletions
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7
mm/memcontrol.c
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@ -592,7 +592,7 @@ static DECLARE_DEFERRABLE_WORK(stats_flush_dwork, flush_memcg_stats_dwork);
static DEFINE_PER_CPU(unsigned int, stats_updates); static DEFINE_PER_CPU(unsigned int, stats_updates);
static atomic_t stats_flush_ongoing = ATOMIC_INIT(0); static atomic_t stats_flush_ongoing = ATOMIC_INIT(0);
static atomic_t stats_flush_threshold = 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) #define FLUSH_TIME (2UL*HZ)
@ -652,7 +652,7 @@ static void do_flush_stats(void)
atomic_xchg(&stats_flush_ongoing, 1)) atomic_xchg(&stats_flush_ongoing, 1))
return; 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); cgroup_rstat_flush(root_mem_cgroup->css.cgroup);
@ -668,7 +668,8 @@ void mem_cgroup_flush_stats(void)
void mem_cgroup_flush_stats_ratelimited(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(); mem_cgroup_flush_stats();
} }