Patch "mm: memcg: change flush_next_time to flush_last_time" has been added to the 6.6-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    mm: memcg: change flush_next_time to flush_last_time

to the 6.6-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     mm-memcg-change-flush_next_time-to-flush_last_time.patch
and it can be found in the queue-6.6 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


From leon.huangfu@shopee.com Mon Nov  3 08:53:16 2025
From: Leon Huang Fu <leon.huangfu@shopee.com>
Date: Mon,  3 Nov 2025 15:51:31 +0800
Subject: mm: memcg: change flush_next_time to flush_last_time
To: stable@vger.kernel.org, greg@kroah.com
Cc: tj@kernel.org, lizefan.x@bytedance.com, hannes@cmpxchg.org, corbet@lwn.net, mhocko@kernel.org, roman.gushchin@linux.dev, shakeelb@google.com, muchun.song@linux.dev, akpm@linux-foundation.org, sjenning@redhat.com, ddstreet@ieee.org, vitaly.wool@konsulko.com, lance.yang@linux.dev, leon.huangfu@shopee.com, shy828301@gmail.com, yosryahmed@google.com, sashal@kernel.org, vishal.moola@gmail.com, cerasuolodomenico@gmail.com, nphamcs@gmail.com, cgroups@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Chris Li <chrisl@kernel.org>, Bagas Sanjaya <bagasdotme@gmail.com>, Greg Thelen <gthelen@google.com>, Ivan Babrou <ivan@cloudflare.com>, Michal Koutny <mkoutny@suse.com>, Waiman Long <longman@redhat.com>, Wei Xu <weixugc@google.com>
Message-ID: <20251103075135.20254-4-leon.huangfu@shopee.com>

From: Yosry Ahmed <yosryahmed@google.com>

[ Upstream commit 508bed884767a8eb394640bae9edcdf082816c43 ]

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 <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>
Signed-off-by: Leon Huang Fu <leon.huangfu@shopee.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 mm/memcontrol.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -590,7 +590,7 @@ static DECLARE_DEFERRABLE_WORK(stats_flu
 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)
 
@@ -650,7 +650,7 @@ 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);
 
@@ -666,7 +666,8 @@ 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();
 }
 


Patches currently in stable-queue which might be from leon.huangfu@shopee.com are

queue-6.6/mm-memcg-make-stats-flushing-threshold-per-memcg.patch
queue-6.6/mm-memcg-change-flush_next_time-to-flush_last_time.patch
queue-6.6/mm-memcg-restore-subtree-stats-flushing.patch
queue-6.6/mm-workingset-move-the-stats-flush-into-workingset_test_recent.patch
queue-6.6/mm-memcg-add-thp-swap-out-info-for-anonymous-reclaim.patch
queue-6.6/mm-memcg-add-per-memcg-zswap-writeback-stat.patch
queue-6.6/mm-memcg-move-vmstats-structs-definition-above-flushing-code.patch