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 X-Spam-Level: X-Spam-Status: No, score=-5.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B4FE0C433DF for ; Tue, 18 Aug 2020 16:14:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8013B207DA for ; Tue, 18 Aug 2020 16:14:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1597767241; bh=i/osbT4JGLM2WHPj4a6FDQcQ9reu9lXtYu+uvpCBQEE=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=WL0rJRKf8+2yzrT+YOO2HS3IVlVrY+gabK4oLWpKpDSmGW7aQhts2LU5yTokKwJro znSXC9voufkFnAH4kGfSJqWJcTy/Js0BYcJ1Ai9rUcPKLMZLgfH3JciiJWEcBtp321 41V/nmLWd7UQcdyw+QsivKGe+yjBwIjag41DSV1k= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726870AbgHRQN6 (ORCPT ); Tue, 18 Aug 2020 12:13:58 -0400 Received: from mail.kernel.org ([198.145.29.99]:50000 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726633AbgHRQN4 (ORCPT ); Tue, 18 Aug 2020 12:13:56 -0400 Received: from paulmck-ThinkPad-P72.home (unknown [50.45.173.55]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 596F4207DA; Tue, 18 Aug 2020 16:13:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1597767235; bh=i/osbT4JGLM2WHPj4a6FDQcQ9reu9lXtYu+uvpCBQEE=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=03MprkvPlHzEHpFG/RyjOx9tNAFMVa1A41U0L+2ALSxA7w6D+tul3V8CY1pTehgoq ITIuXMiwan2NvpAe3sKyhJWrBvuWUyJMhI9ooE+UpM2qe2DXxlzlpIAuMoDXh47oav l8MxfSgyn6Qa9lYNFTgrLRd7pWzhg9E1ONtUVjEA= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 30C4135228F5; Tue, 18 Aug 2020 09:13:55 -0700 (PDT) Date: Tue, 18 Aug 2020 09:13:55 -0700 From: "Paul E. McKenney" To: Thomas Gleixner Cc: Michal Hocko , Uladzislau Rezki , Peter Zijlstra , LKML , RCU , linux-mm@kvack.org, Andrew Morton , Vlastimil Babka , Matthew Wilcox , "Theodore Y . Ts'o" , Joel Fernandes , Sebastian Andrzej Siewior , Oleksiy Avramchenko Subject: Re: [RFC-PATCH 1/2] mm: Add __GFP_NO_LOCKS flag Message-ID: <20200818161355.GE27891@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20200814180224.GQ4295@paulmck-ThinkPad-P72> <875z9lkoo4.fsf@nanos.tec.linutronix.de> <20200814204140.GT4295@paulmck-ThinkPad-P72> <20200814215206.GL3982@worktop.programming.kicks-ass.net> <20200816225655.GA17869@pc636> <20200817082849.GA28270@dhcp22.suse.cz> <20200817222803.GE23602@paulmck-ThinkPad-P72> <20200818074344.GL28270@dhcp22.suse.cz> <20200818135327.GF23602@paulmck-ThinkPad-P72> <87o8n8hv5p.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87o8n8hv5p.fsf@nanos.tec.linutronix.de> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Aug 18, 2020 at 04:43:14PM +0200, Thomas Gleixner wrote: > On Tue, Aug 18 2020 at 06:53, Paul E. McKenney wrote: > > On Tue, Aug 18, 2020 at 09:43:44AM +0200, Michal Hocko wrote: > >> Thomas had a good point that it doesn't really make much sense to > >> optimize for flooders because that just makes them more effective. > > > > The point is not to make the flooders go faster, but rather for the > > system to be robust in the face of flooders. Robust as in harder for > > a flooder to OOM the system. > > > > And reducing the number of post-grace-period cache misses makes it > > easier for the callback-invocation-time memory freeing to keep up with > > the flooder, thus avoiding (or at least delaying) the OOM. > > Throttling the flooder is incresing robustness far more than reducing > cache misses. True, but it takes time to identify a flooding event that needs to be throttled (as in milliseconds). This time cannot be made up. And in the absence of a flooding event, the last thing you want to do is to throttle call_rcu(), kfree_rcu(), and kvfree_rcu(). Thanx, Paul