From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.zx2c4.com (lists.zx2c4.com [165.227.139.114]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 96952C27C4F for ; Thu, 13 Jun 2024 18:00:02 +0000 (UTC) Received: by lists.zx2c4.com (ZX2C4 Mail Server) with ESMTP id 8926dccd; Thu, 13 Jun 2024 17:58:23 +0000 (UTC) Received: from mail-lj1-x22b.google.com (mail-lj1-x22b.google.com [2a00:1450:4864:20::22b]) by lists.zx2c4.com (ZX2C4 Mail Server) with ESMTPS id 1cb0affe (TLSv1.3:TLS_AES_256_GCM_SHA384:256:NO) for ; Thu, 13 Jun 2024 17:58:22 +0000 (UTC) Received: by mail-lj1-x22b.google.com with SMTP id 38308e7fff4ca-2ec0f3b9cfeso1754091fa.0 for ; Thu, 13 Jun 2024 10:58:22 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1718301502; x=1718906302; darn=lists.zx2c4.com; h=in-reply-to:content-transfer-encoding:content-disposition :mime-version:references:message-id:subject:cc:to:date:from:from:to :cc:subject:date:message-id:reply-to; bh=LJdaR0AKwDxb6UxD8VgG/YvgQDgT5IhbR4y3pM8S3I4=; b=gPp4Lw4zmT+qh0Onlf9cUczYDj2XWUp8hUNElK3iG55U+LW7UW9OwCrUkoX42Wvv+q /7IxHqFQT297a5KeUZFQIFQk2o8jN4CbZbB+zxEAagg6WuRvVFCcrgf7j09zwviIvbvz /hd0GK9havG7xX6f/kcfz8b1C4ROvD6/OodEbkgIb2i7magt1vh2ET8Mpjb6OWAFrThz Imh2A/0RpR/Wc5PmVqxF5CBuqS4BpxBWr1R+ZTg/lOApup6qQ5gg/0xwEStMHF+Nw9bf aKpkZpGfQs+fauXHG+58JlKUNsZN6Y+LcVvkyBoQME7n2aGStkkjOl9UL0BxOaQR5aD6 f+Pw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1718301502; x=1718906302; h=in-reply-to:content-transfer-encoding:content-disposition :mime-version:references:message-id:subject:cc:to:date:from :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=LJdaR0AKwDxb6UxD8VgG/YvgQDgT5IhbR4y3pM8S3I4=; b=ixnr+49gJ/P3peZVnbh73FRY4Vd0vhwP1rE7OAihtTyiM/rnRjAZ1OU6hnFjC7CNqk JQj/fjoe1JGGudiTJW3670nmBNo49oU/VAIl2/iMFyeh7ntQZWXvezfrCmmHuqLyBmhU 6slC3SZLVkJznbKgLChvlvMA5D0/cAhBrY8U+0zPKgUpW4ImIbEITkMiFPyC2RGIRzkw GC4/Wk8Cn5jpPWfhTnlCifNTSwDY2aKQZFn4hVfIn8P+0oqKYwGSE2aM7jbNdTimzTbh kuExF5Qrq1pVWKptERZo51crmSHuxmnTyn4lZ8DCV9o02cCvrcSSoIVYLwD+h9AN8Z8j 9mFQ== X-Forwarded-Encrypted: i=1; AJvYcCUGaW5BtgCjLMS40i2Az/KafMlE80owYKXrP8rEkgGaUaE+kukL7ralOEwNQtYrRHCz3wuV0ynwG4bUrtclpW6+yYwTdLz89JZo X-Gm-Message-State: AOJu0Yz9pSH5UDqpAXgkX5UxJx+fc6/nwYvWoGrDr84/EK0Nq5BJ0iJW 6NJn4wTNMuUGTd3mbpd2LzlO48Hpsiy27949FWIAcyY3hiKduclU X-Google-Smtp-Source: AGHT+IEhErzyVFwc5vrtNZW2dG954f3qNIGROFYFFTe33sAR7d1zhfiUTqk8uRw2thbyuYd+W2q+QA== X-Received: by 2002:a2e:9dd4:0:b0:2ec:453:e46e with SMTP id 38308e7fff4ca-2ec0e5a0442mr3954341fa.42.1718301501351; Thu, 13 Jun 2024 10:58:21 -0700 (PDT) Received: from pc636 (host-90-233-218-141.mobileonline.telia.com. [90.233.218.141]) by smtp.gmail.com with ESMTPSA id 38308e7fff4ca-2ec05c8a85esm3330101fa.117.2024.06.13.10.58.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 13 Jun 2024 10:58:20 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Thu, 13 Jun 2024 19:58:17 +0200 To: "Paul E. McKenney" Cc: Uladzislau Rezki , Vlastimil Babka , "Jason A. Donenfeld" , Jakub Kicinski , Julia Lawall , linux-block@vger.kernel.org, kernel-janitors@vger.kernel.org, bridge@lists.linux.dev, linux-trace-kernel@vger.kernel.org, Mathieu Desnoyers , kvm@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, "Naveen N. Rao" , Christophe Leroy , Nicholas Piggin , netdev@vger.kernel.org, wireguard@lists.zx2c4.com, linux-kernel@vger.kernel.org, ecryptfs@vger.kernel.org, Neil Brown , Olga Kornievskaia , Dai Ngo , Tom Talpey , linux-nfs@vger.kernel.org, linux-can@vger.kernel.org, Lai Jiangshan , 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: References: <20240609082726.32742-1-Julia.Lawall@inria.fr> <20240612143305.451abf58@kernel.org> <80e03b02-7e24-4342-af0b-ba5117b19828@paulmck-laptop> <7efde25f-6af5-4a67-abea-b26732a8aca1@paulmck-laptop> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-BeenThere: wireguard@lists.zx2c4.com X-Mailman-Version: 2.1.30rc1 Precedence: list List-Id: Development discussion of WireGuard List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: wireguard-bounces@lists.zx2c4.com Sender: "WireGuard" On Thu, Jun 13, 2024 at 10:45:59AM -0700, Paul E. McKenney wrote: > On Thu, Jun 13, 2024 at 07:38:59PM +0200, Uladzislau Rezki wrote: > > On Thu, Jun 13, 2024 at 08:06:30AM -0700, Paul E. McKenney wrote: > > > On Thu, Jun 13, 2024 at 03:06:54PM +0200, Uladzislau Rezki wrote: > > > > On Thu, Jun 13, 2024 at 05:47:08AM -0700, Paul E. McKenney wrote: > > > > > On Thu, Jun 13, 2024 at 01:58:59PM +0200, Jason A. Donenfeld wrote: > > > > > > On Wed, Jun 12, 2024 at 03:37:55PM -0700, Paul E. McKenney wrote: > > > > > > > On Wed, Jun 12, 2024 at 02:33:05PM -0700, Jakub Kicinski wrote: > > > > > > > > On Sun, 9 Jun 2024 10:27:12 +0200 Julia Lawall wrote: > > > > > > > > > Since SLOB was removed, it is not necessary to use call_rcu > > > > > > > > > when the callback only performs kmem_cache_free. Use > > > > > > > > > kfree_rcu() directly. > > > > > > > > > > > > > > > > > > The changes were done using the following Coccinelle semantic patch. > > > > > > > > > This semantic patch is designed to ignore cases where the callback > > > > > > > > > function is used in another way. > > > > > > > > > > > > > > > > How does the discussion on: > > > > > > > > [PATCH] Revert "batman-adv: prefer kfree_rcu() over call_rcu() with free-only callbacks" > > > > > > > > https://lore.kernel.org/all/20240612133357.2596-1-linus.luessing@c0d3.blue/ > > > > > > > > reflect on this series? IIUC we should hold off.. > > > > > > > > > > > > > > We do need to hold off for the ones in kernel modules (such as 07/14) > > > > > > > where the kmem_cache is destroyed during module unload. > > > > > > > > > > > > > > OK, I might as well go through them... > > > > > > > > > > > > > > [PATCH 01/14] wireguard: allowedips: replace call_rcu by kfree_rcu for simple kmem_cache_free callback > > > > > > > Needs to wait, see wg_allowedips_slab_uninit(). > > > > > > > > > > > > Also, notably, this patch needs additionally: > > > > > > > > > > > > diff --git a/drivers/net/wireguard/allowedips.c b/drivers/net/wireguard/allowedips.c > > > > > > index e4e1638fce1b..c95f6937c3f1 100644 > > > > > > --- a/drivers/net/wireguard/allowedips.c > > > > > > +++ b/drivers/net/wireguard/allowedips.c > > > > > > @@ -377,7 +377,6 @@ int __init wg_allowedips_slab_init(void) > > > > > > > > > > > > void wg_allowedips_slab_uninit(void) > > > > > > { > > > > > > - rcu_barrier(); > > > > > > kmem_cache_destroy(node_cache); > > > > > > } > > > > > > > > > > > > Once kmem_cache_destroy has been fixed to be deferrable. > > > > > > > > > > > > I assume the other patches are similar -- an rcu_barrier() can be > > > > > > removed. So some manual meddling of these might be in order. > > > > > > > > > > Assuming that the deferrable kmem_cache_destroy() is the option chosen, > > > > > agreed. > > > > > > > > > > > > > void kmem_cache_destroy(struct kmem_cache *s) > > > > { > > > > int err = -EBUSY; > > > > bool rcu_set; > > > > > > > > if (unlikely(!s) || !kasan_check_byte(s)) > > > > return; > > > > > > > > cpus_read_lock(); > > > > mutex_lock(&slab_mutex); > > > > > > > > rcu_set = s->flags & SLAB_TYPESAFE_BY_RCU; > > > > > > > > s->refcount--; > > > > if (s->refcount) > > > > goto out_unlock; > > > > > > > > err = shutdown_cache(s); > > > > WARN(err, "%s %s: Slab cache still has objects when called from %pS", > > > > __func__, s->name, (void *)_RET_IP_); > > > > ... > > > > cpus_read_unlock(); > > > > if (!err && !rcu_set) > > > > kmem_cache_release(s); > > > > } > > > > > > > > > > > > so we have SLAB_TYPESAFE_BY_RCU flag that defers freeing slab-pages > > > > and a cache by a grace period. Similar flag can be added, like > > > > SLAB_DESTROY_ONCE_FULLY_FREED, in this case a worker rearm itself > > > > if there are still objects which should be freed. > > > > > > > > Any thoughts here? > > > > > > Wouldn't we also need some additional code to later check for all objects > > > being freed to the slab, whether or not that code is initiated from > > > kmem_cache_destroy()? > > > > > Same away as SLAB_TYPESAFE_BY_RCU is handled from the kmem_cache_destroy() function. > > It checks that flag and if it is true and extra worker is scheduled to perform a > > deferred(instead of right away) destroy after rcu_barrier() finishes. > > Like this? > > SLAB_DESTROY_ONCE_FULLY_FREED > > Instead of adding a new kmem_cache_destroy_rcu() > or kmem_cache_destroy_wait() API member, instead add a > SLAB_DESTROY_ONCE_FULLY_FREED flag that can be passed to the > existing kmem_cache_destroy() function.  Use of this flag would > suppress any warnings that would otherwise be issued if there > was still slab memory yet to be freed, and it would also spawn > workqueues (or timers or whatever) to do any needed cleanup work. > > The flag is passed as all others during creating a cache: slab = kmem_cache_create(name, size, ..., SLAB_DESTROY_ONCE_FULLY_FREED | OTHER_FLAGS, NULL); the rest description is correct to me. -- Uladzislau Rezki