From: Roman Gushchin <roman.gushchin@linux.dev>
To: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Johannes Weiner <hannes@cmpxchg.org>,
Michal Hocko <mhocko@kernel.org>,
Muchun Song <muchun.song@linux.dev>,
Yosry Ahmed <yosry.ahmed@linux.dev>,
Waiman Long <llong@redhat.com>,
linux-mm@kvack.org, cgroups@vger.kernel.org,
linux-kernel@vger.kernel.org,
Meta kernel team <kernel-team@meta.com>
Subject: Re: [PATCH] memcg: no refill for offlined objcg
Date: Thu, 10 Apr 2025 23:59:47 +0000 [thread overview]
Message-ID: <7ia47c3r1sb0.fsf@castle.c.googlers.com> (raw)
In-Reply-To: <20250410210535.1005312-1-shakeel.butt@linux.dev> (Shakeel Butt's message of "Thu, 10 Apr 2025 14:05:35 -0700")
Shakeel Butt <shakeel.butt@linux.dev> writes:
> In our fleet, we are observing refill_obj_stock() spending a lot of cpu
> in obj_cgroup_get() and on further inspection it seems like the given
> objcg is offlined and the kernel has to take the slow path i.e. atomic
> operations for objcg reference counting.
>
> Other than expensive atomic operations, refilling stock of an offlined
> objcg is a waster as there will not be new allocations for the offlined
> objcg. In addition, refilling triggers flush of the previous objcg which
> might be used in future. So, let's just avoid refilling the stock with
> the offlined objcg.
Hm, but on the other side if there are multiple uncharges in a row,
refilling obj stocks might be still cheaper?
In general I think that switching to atomic css refcnt on memcg
offlining is a mistake - it makes memory reclaim generally more
expensive. We can simple delay it until the approximate refcnt
number reaches some low value, e.g. 100 objects.
next prev parent reply other threads:[~2025-04-10 23:59 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-04-10 21:05 Shakeel Butt
2025-04-10 23:59 ` Roman Gushchin [this message]
2025-04-14 18:44 ` Shakeel Butt
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