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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id C3635C25B4E for ; Fri, 20 Jan 2023 17:21:45 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 37D746B0092; Fri, 20 Jan 2023 12:21:45 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 32DC36B0093; Fri, 20 Jan 2023 12:21:45 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 1F5046B0095; Fri, 20 Jan 2023 12:21:45 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id 0B0F26B0092 for ; Fri, 20 Jan 2023 12:21:45 -0500 (EST) Received: from smtpin18.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id D0670140E06 for ; Fri, 20 Jan 2023 17:21:44 +0000 (UTC) X-FDA: 80375844528.18.C742ACF Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by imf07.hostedemail.com (Postfix) with ESMTP id ECB3F40016 for ; Fri, 20 Jan 2023 17:21:42 +0000 (UTC) Authentication-Results: imf07.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=Kfdej4Nj; spf=pass (imf07.hostedemail.com: domain of "SRS0=LVeK=5R=paulmck-ThinkPad-P17-Gen-1.home=paulmck@kernel.org" designates 139.178.84.217 as permitted sender) smtp.mailfrom="SRS0=LVeK=5R=paulmck-ThinkPad-P17-Gen-1.home=paulmck@kernel.org"; dmarc=pass (policy=none) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1674235303; h=from:from:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=QTpbrtTEVwZObinvel01XrvAfodbg87IQcO+mM7MxPQ=; b=06uhbtmtPgPFxxRtg1Il93uWZ8wh/dYNfIY8AyJoIIhixBuQSQv3MQG7gUaNFmB18Mgkdx CYx8LGVv7oifQyPN5pq78Gm6bpCpfMJ9fa/K/PYAGabhWaYiRur7oaMCXiiPrBQuH0uNAe S2DU19KsdhJ8dLY29PZ6qN4C5a0L1mI= ARC-Authentication-Results: i=1; imf07.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=Kfdej4Nj; spf=pass (imf07.hostedemail.com: domain of "SRS0=LVeK=5R=paulmck-ThinkPad-P17-Gen-1.home=paulmck@kernel.org" designates 139.178.84.217 as permitted sender) smtp.mailfrom="SRS0=LVeK=5R=paulmck-ThinkPad-P17-Gen-1.home=paulmck@kernel.org"; dmarc=pass (policy=none) header.from=kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1674235303; a=rsa-sha256; cv=none; b=7u+WIuYlOyQ87gb04/hjyhtqBTMoBMHItyszgQyZ3AQtYHgB+ZMwC6Vn4mcz/kzkHoPqWw OV7vl0xmCz4a1SR6iIWwBGYFV9Ic3w1IyKEPgmMjRc5ihkdHwKgWMrjckXU/g2mnSnyBqf kXpg/YJBdOElV7fK0mTHcsIFc8gAwbE= Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id D486D62024; Fri, 20 Jan 2023 17:21:41 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id F3F22C433A1; Fri, 20 Jan 2023 17:21:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1674235301; bh=I1qTWw2OMTpCQGNS0oCnz+DeLugW7m0MkCxFsFb/Dak=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=Kfdej4NjVMobPhJ3rE/PMAzza8oADmNlkGqiZYGqRvTSIUQdTHKRd6NHGGwNKg8g4 Wv67aWSm+XPbi1RBoo3IcSzQxQNxls+vkqagf4zovgJuG5e5YtyX6zoONtyfcnsHr/ MmszMAR/PoZVZaQ2ZUmMiK+VbMH8Nxupenpd4yEa4t3V07RSClxZbnlZ9l7Bxy/Eha 7l4dxYe+UKqgg6a7G6pQcoxZWuDHr9mOJgi4qoCp2cwXyt1YcH92lwoAsO8udPKTIu N9GMcWwfBWm9lgbgj4KzGHOF1wWRo+bYyHu/V0BAlDo1pzAH3QCCu2hHfcUhjy3Azr AmgM+CiHvme9Q== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 8BB745C17DC; Fri, 20 Jan 2023 09:21:40 -0800 (PST) Date: Fri, 20 Jan 2023 09:21:40 -0800 From: "Paul E. McKenney" To: Matthew Wilcox Cc: Suren Baghdasaryan , Michal Hocko , akpm@linux-foundation.org, michel@lespinasse.org, jglisse@google.com, vbabka@suse.cz, hannes@cmpxchg.org, mgorman@techsingularity.net, dave@stgolabs.net, liam.howlett@oracle.com, peterz@infradead.org, ldufour@linux.ibm.com, laurent.dufour@fr.ibm.com, luto@kernel.org, songliubraving@fb.com, peterx@redhat.com, david@redhat.com, dhowells@redhat.com, hughd@google.com, bigeasy@linutronix.de, kent.overstreet@linux.dev, punit.agrawal@bytedance.com, lstoakes@gmail.com, peterjung1337@gmail.com, rientjes@google.com, axelrasmussen@google.com, joelaf@google.com, minchan@google.com, jannh@google.com, shakeelb@google.com, tatashin@google.com, edumazet@google.com, gthelen@google.com, gurua@google.com, arjunroy@google.com, soheil@google.com, hughlynch@google.com, leewalsh@google.com, posk@google.com, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, x86@kernel.org, linux-kernel@vger.kernel.org, kernel-team@android.com Subject: Re: [PATCH 39/41] kernel/fork: throttle call_rcu() calls in vm_area_free Message-ID: <20230120172140.GL2948950@paulmck-ThinkPad-P17-Gen-1> Reply-To: paulmck@kernel.org References: <20230109205336.3665937-1-surenb@google.com> <20230109205336.3665937-40-surenb@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Server: rspam03 X-Stat-Signature: 5pwbzqt6z7q7iruq6o5fz1mjyicqwdm5 X-Rspamd-Queue-Id: ECB3F40016 X-HE-Tag: 1674235302-406989 X-HE-Meta: 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 KJFUCtR3 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, Jan 20, 2023 at 04:49:42PM +0000, Matthew Wilcox wrote: > On Fri, Jan 20, 2023 at 08:45:21AM -0800, Suren Baghdasaryan wrote: > > On Fri, Jan 20, 2023 at 8:20 AM Suren Baghdasaryan wrote: > > > > > > On Fri, Jan 20, 2023 at 12:52 AM Michal Hocko wrote: > > > > > > > > On Thu 19-01-23 10:52:03, Suren Baghdasaryan wrote: > > > > > On Thu, Jan 19, 2023 at 4:59 AM Michal Hocko wrote: > > > > > > > > > > > > On Mon 09-01-23 12:53:34, Suren Baghdasaryan wrote: > > > > > > > call_rcu() can take a long time when callback offloading is enabled. > > > > > > > Its use in the vm_area_free can cause regressions in the exit path when > > > > > > > multiple VMAs are being freed. To minimize that impact, place VMAs into > > > > > > > a list and free them in groups using one call_rcu() call per group. > > > > > > > > > > > > After some more clarification I can understand how call_rcu might not be > > > > > > super happy about thousands of callbacks to be invoked and I do agree > > > > > > that this is not really optimal. > > > > > > > > > > > > On the other hand I do not like this solution much either. > > > > > > VM_AREA_FREE_LIST_MAX is arbitrary and it won't really help all that > > > > > > much with processes with a huge number of vmas either. It would still be > > > > > > in housands of callbacks to be scheduled without a good reason. > > > > > > > > > > > > Instead, are there any other cases than remove_vma that need this > > > > > > batching? We could easily just link all the vmas into linked list and > > > > > > use a single call_rcu instead, no? This would both simplify the > > > > > > implementation, remove the scaling issue as well and we do not have to > > > > > > argue whether VM_AREA_FREE_LIST_MAX should be epsilon or epsilon + 1. > > > > > > > > > > Yes, I agree the solution is not stellar. I wanted something simple > > > > > but this is probably too simple. OTOH keeping all dead vm_area_structs > > > > > on the list without hooking up a shrinker (additional complexity) does > > > > > not sound too appealing either. > > > > > > > > I suspect you have missed my idea. I do not really want to keep the list > > > > around or any shrinker. It is dead simple. Collect all vmas in > > > > remove_vma and then call_rcu the whole list at once after the whole list > > > > (be it from exit_mmap or remove_mt). See? > > > > > > Yes, I understood your idea but keeping dead objects until the process > > > exits even when the system is low on memory (no shrinkers attached) > > > seems too wasteful. If we do this I would advocate for attaching a > > > shrinker. > > > > Maybe even simpler, since we are hit with this VMA freeing flood > > during exit_mmap (when all VMAs are destroyed), we pass a hint to > > vm_area_free to batch the destruction and all other cases call > > call_rcu()? I don't think there will be other cases of VMA destruction > > floods. > > ... or have two different call_rcu functions; one for munmap() and > one for exit. It'd be nice to use kmem_cache_free_bulk(). Good point, kfree_rcu(p, r) where "r" is the name of the rcu_head structure's field, is much more cache-efficient. The penalty is that there is no callback function to do any cleanup. There is just a kfree()/kvfree (bulk version where applicable), nothing else. Thanx, Paul