linux-kernel - [RFC PATCH 05/10] memcg: no refilling stock from obj_cgroup

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Message-ID: <20250314061511.1308152-6-shakeel.butt@linux.dev>
Date: Thu, 13 Mar 2025 23:15:06 -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: [RFC PATCH 05/10] memcg: no refilling stock from obj_cgroup_release

obj_cgroup_release is called when all the references to the objcg has
been released i.e. no more memory objects are pointing to it. Most
probably objcg->memcg will be pointing to some ancestor memcg and at the
moment, in obj_cgroup_release, the kernel call
obj_cgroup_uncharge_pages() to uncharge last remaining memory.

However obj_cgroup_uncharge_pages() refills the local stock. There is
no need to refill the local stock with some ancestor memcg and flush the
local stock. In addition this removes the requirement to only call
obj_cgroup_put() outside of local_lock.

Signed-off-by: Shakeel Butt <shakeel.butt@...ux.dev>
---
 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