linux-kernel - [PATCH 5/9] memcg: no refilling stock from obj_cgroup

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Message-ID: <20250315174930.1769599-6-shakeel.butt@linux.dev>
Date: Sat, 15 Mar 2025 10:49:26 -0700
From: Shakeel Butt <shakeel.butt@...ux.dev>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...nel.org>,
	Roman Gushchin <roman.gushchin@...ux.dev>,
	Muchun Song <muchun.song@...ux.dev>,
	Vlastimil Babka <vbabka@...e.cz>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	linux-mm@...ck.org,
	cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Meta kernel team <kernel-team@...a.com>
Subject: [PATCH 5/9] memcg: no refilling stock from obj_cgroup_release

obj_cgroup_release is called when all the references to the objcg have
been released i.e. no more memory objects are pointing to it. Most
probably objcg->memcg will be pointing to some ancestor memcg. In
obj_cgroup_release(), the kernel calls obj_cgroup_uncharge_pages() which
refills the local stock.

There is no need to refill the local stock with some ancestor memcg and
flush the local stock. Let's decouple obj_cgroup_release() from the
local stock by uncharging instead of refilling. One additional benefit
of this change is that it removes the requirement to only call
obj_cgroup_put() outside of local_lock.

Signed-off-by: Shakeel Butt <shakeel.butt@...ux.dev>
Acked-by: Vlastimil Babka <vbabka@...e.cz>
---
 mm/memcontrol.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 7054b0ebd207..83db180455a1 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -129,8 +129,7 @@ bool mem_cgroup_kmem_disabled(void)
 	return cgroup_memory_nokmem;
 }
 
-static void obj_cgroup_uncharge_pages(struct obj_cgroup *objcg,
-				      unsigned int nr_pages);
+static void memcg_uncharge(struct mem_cgroup *memcg, unsigned int nr_pages);
 
 static void obj_cgroup_release(struct percpu_ref *ref)
 {
@@ -163,8 +162,16 @@ static void obj_cgroup_release(struct percpu_ref *ref)
 	WARN_ON_ONCE(nr_bytes & (PAGE_SIZE - 1));
 	nr_pages = nr_bytes >> PAGE_SHIFT;
 
-	if (nr_pages)
-		obj_cgroup_uncharge_pages(objcg, nr_pages);
+	if (nr_pages) {
+		struct mem_cgroup *memcg;
+
+		memcg = get_mem_cgroup_from_objcg(objcg);
+		mod_memcg_state(memcg, MEMCG_KMEM, -nr_pages);
+		memcg1_account_kmem(memcg, -nr_pages);
+		if (!mem_cgroup_is_root(memcg))
+			memcg_uncharge(memcg, nr_pages);
+		css_put(&memcg->css);
+	}
 
 	spin_lock_irqsave(&objcg_lock, flags);
 	list_del(&objcg->list);
-- 
2.47.1