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memcg: no refilling stock from obj_cgroup_release

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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.

Link: https://lkml.kernel.org/r/20250404013913.1663035-6-shakeel.butt@linux.dev
Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Shakeel Butt 2025-04-03 18:39:09 -07:00 committed by Andrew Morton
parent cbc091441d
commit b6d0471117
1 changed files with 11 additions and 4 deletions
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15
mm/memcontrol.c
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@ -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);
mem_cgroup_put(memcg);
}
spin_lock_irqsave(&objcg_lock, flags);
list_del(&objcg->list);