The patch titled Subject: mm: memcg: remove stats flushing mutex has been added to the -mm mm-unstable branch. Its filename is mm-memcg-restore-subtree-stats-flushing-fix-2.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-memcg-restore-subtree-stats-flushing-fix-2.patch This patch will later appear in the mm-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via the mm-everything branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there every 2-3 working days ------------------------------------------------------ From: Yosry Ahmed <yosryahmed@xxxxxxxxxx> Subject: mm: memcg: remove stats flushing mutex Date: Mon, 4 Dec 2023 23:43:29 +0000 The mutex was intended to make the waiters sleep instead of spin, and such that we can check the update thresholds again after acquiring the mutex. However, the mutex has a risk of priority inversion, especially since the underlying rstat lock can de dropped while the mutex is held. Synthetic testing with high concurrency of flushers shows no regressions without the mutex, so remove it. Link: https://lkml.kernel.org/r/CAJD7tkZgP3m-VVPn+fF_YuvXeQYK=tZZjJHj=dzD=CcSSpp2qg@xxxxxxxxxxxxxx Signed-off-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx> Suggested-by: Shakeel Butt <shakeelb@xxxxxxxxxx> Acked-by: Shakeel Butt <shakeelb@xxxxxxxxxx> Cc: Chris Li <chrisl@xxxxxxxxxx> Cc: Domenico Cerasuolo <cerasuolodomenico@xxxxxxxxx> Cc: Greg Thelen <gthelen@xxxxxxxxxx> Cc: Ivan Babrou <ivan@xxxxxxxxxxxxxx> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxxxx> Cc: Michal Koutny <mkoutny@xxxxxxxx> Cc: Muchun Song <muchun.song@xxxxxxxxx> Cc: Roman Gushchin <roman.gushchin@xxxxxxxxx> Cc: Tejun Heo <tj@xxxxxxxxxx> Cc: Waiman Long <longman@xxxxxxxxxx> Cc: Wei Xu <weixugc@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/memcontrol.c | 11 ++--------- 1 file changed, 2 insertions(+), 9 deletions(-) --- a/mm/memcontrol.c~mm-memcg-restore-subtree-stats-flushing-fix-2 +++ a/mm/memcontrol.c @@ -749,21 +749,14 @@ static void do_flush_stats(struct mem_cg */ void mem_cgroup_flush_stats(struct mem_cgroup *memcg) { - static DEFINE_MUTEX(memcg_stats_flush_mutex); - if (mem_cgroup_disabled()) return; if (!memcg) memcg = root_mem_cgroup; - if (memcg_should_flush_stats(memcg)) { - mutex_lock(&memcg_stats_flush_mutex); - /* Check again after locking, another flush may have occurred */ - if (memcg_should_flush_stats(memcg)) - do_flush_stats(memcg); - mutex_unlock(&memcg_stats_flush_mutex); - } + if (memcg_should_flush_stats(memcg)) + do_flush_stats(memcg); } void mem_cgroup_flush_stats_ratelimited(struct mem_cgroup *memcg) _ Patches currently in -mm which might be from yosryahmed@xxxxxxxxxx are mm-memcg-change-flush_next_time-to-flush_last_time.patch mm-memcg-move-vmstats-structs-definition-above-flushing-code.patch mm-memcg-make-stats-flushing-threshold-per-memcg.patch mm-workingset-move-the-stats-flush-into-workingset_test_recent.patch mm-memcg-restore-subtree-stats-flushing.patch mm-memcg-restore-subtree-stats-flushing-fix-2.patch