The patch titled
Subject: memcg: avoid refill_stock for root memcg
has been added to the -mm mm-unstable branch. Its filename is
memcg-avoid-refill_stock-for-root-memcg.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/memcg-avoid-refill_stock-for-root-memcg.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Shakeel Butt <shakeel.butt@xxxxxxxxx>
Subject: memcg: avoid refill_stock for root memcg
Date: Wed, 12 Mar 2025 22:48:12 -0700
We never charge the page counters of root memcg, so there is no need to
put root memcg in the memcg stock. At the moment, refill_stock() can be
called from try_charge_memcg(), obj_cgroup_uncharge_pages() and
mem_cgroup_uncharge_skmem().
The try_charge_memcg() and mem_cgroup_uncharge_skmem() are never called
with root memcg, so those are fine. However obj_cgroup_uncharge_pages()
can potentially call refill_stock() with root memcg if the objcg object
has been reparented over to the root memcg. Let's just avoid
refill_stock() from obj_cgroup_uncharge_pages() for root memcg.
Link: https://lkml.kernel.org/r/20250313054812.2185900-1-shakeel.butt@xxxxxxxxx
Signed-off-by: Shakeel Butt <shakeel.butt@xxxxxxxxx>
Acked-by: Michal Hocko <mhockoc@xxxxxxxx>
Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Muchun Song <muchun.song@xxxxxxxxx>
Cc: Roman Gushchin <roman.gushchin@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memcontrol.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
--- a/mm/memcontrol.c~memcg-avoid-refill_stock-for-root-memcg
+++ a/mm/memcontrol.c
@@ -2643,7 +2643,8 @@ static void obj_cgroup_uncharge_pages(st
mod_memcg_state(memcg, MEMCG_KMEM, -nr_pages);
memcg1_account_kmem(memcg, -nr_pages);
- refill_stock(memcg, nr_pages);
+ if (!mem_cgroup_is_root(memcg))
+ refill_stock(memcg, nr_pages);
css_put(&memcg->css);
}
_
Patches currently in -mm which might be from shakeel.butt@xxxxxxxxx are
memcg-drain-obj-stock-on-cpu-hotplug-teardown.patch
memcg-add-hierarchical-effective-limits-for-v2.patch
memcg-dont-call-propagate_protected_usage-for-v1.patch
page_counter-track-failcnt-only-for-legacy-cgroups.patch
page_counter-reduce-struct-page_counter-size.patch
memcg-bypass-root-memcg-check-for-skmem-charging.patch
memcg-avoid-refill_stock-for-root-memcg.patch
