Received-SPF: pass (google.com: domain of linux-nfs+bounces-3847-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:4601:e00::3 as permitted sender) client-ip=2604:1380:4601:e00::3;
Date: Fri, 14 Jun 2024 21:33:45 +0200
From: "Jason A. Donenfeld" <Jason@zx2c4.com>
To: Uladzislau Rezki <urezki@gmail.com>
Cc: "Paul E. McKenney" <paulmck@kernel.org>,
	Vlastimil Babka <vbabka@suse.cz>, Jakub Kicinski <kuba@kernel.org>,
	Julia Lawall <Julia.Lawall@inria.fr>, linux-block@vger.kernel.org,
	kernel-janitors@vger.kernel.org, bridge@lists.linux.dev,
	linux-trace-kernel@vger.kernel.org,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	kvm@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
	"Naveen N. Rao" <naveen.n.rao@linux.ibm.com>,
	Christophe Leroy <christophe.leroy@csgroup.eu>,
	Nicholas Piggin <npiggin@gmail.com>, netdev@vger.kernel.org,
	wireguard@lists.zx2c4.com, linux-kernel@vger.kernel.org,
	ecryptfs@vger.kernel.org, Neil Brown <neilb@suse.de>,
	Olga Kornievskaia <kolga@netapp.com>, Dai Ngo <Dai.Ngo@oracle.com>,
	Tom Talpey <tom@talpey.com>, linux-nfs@vger.kernel.org,
	linux-can@vger.kernel.org, Lai Jiangshan <jiangshanlai@gmail.com>,
	netfilter-devel@vger.kernel.org, coreteam@netfilter.org
Subject: Re: [PATCH 00/14] replace call_rcu by kfree_rcu for simple
 kmem_cache_free callback
Message-ID: <ZmybGZDbXkw7JTjc@zx2c4.com>
References: <baee4d58-17b4-4918-8e45-4d8068a23e8c@paulmck-laptop>
 <ZmrfA1p2zSVIaYam@zx2c4.com>
 <80e03b02-7e24-4342-af0b-ba5117b19828@paulmck-laptop>
 <Zmru7hhz8kPDPsyz@pc636>
 <7efde25f-6af5-4a67-abea-b26732a8aca1@paulmck-laptop>
 <Zmsuswo8OPIhY5KJ@pc636>
 <cb51bc57-47b8-456a-9ac0-f8aa0931b144@paulmck-laptop>
 <ZmszOd5idhf2Cb-v@pc636>
 <b03b007f-3afa-4ad4-b76b-dea7b3aa2bc3@paulmck-laptop>
 <Zmw5FTX752g0vtlD@pc638.lan>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <Zmw5FTX752g0vtlD@pc638.lan>

On Fri, Jun 14, 2024 at 02:35:33PM +0200, Uladzislau Rezki wrote:
> +	/* Should a destroy process be deferred? */
> +	if (s->flags & SLAB_DEFER_DESTROY) {
> +		list_move_tail(&s->list, &slab_caches_defer_destroy);
> +		schedule_delayed_work(&slab_caches_defer_destroy_work, HZ);
> +		goto out_unlock;
> +	}

Wouldn't it be smoother to have the actual kmem_cache_free() function
check to see if it's been marked for destruction and the refcount is
zero, rather than polling every one second? I mentioned this approach
in: https://lore.kernel.org/all/Zmo9-YGraiCj5-MI@zx2c4.com/ -

    I wonder if the right fix to this would be adding a `should_destroy`
    boolean to kmem_cache, which kmem_cache_destroy() sets to true. And
    then right after it checks `if (number_of_allocations == 0)
    actually_destroy()`, and likewise on each kmem_cache_free(), it
    could check `if (should_destroy && number_of_allocations == 0)
    actually_destroy()`. 

Jason