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=-4.3 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 3433AC2D0F2 for ; Tue, 31 Mar 2020 15:34:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 076C820BED for ; Tue, 31 Mar 2020 15:34:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1585668898; bh=Eif2B2ShIJpPgxuw/zOevzktekR3iUQpQKzn/Ra8G2A=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=hZY5ofmJEIcnUskBz+l5OoyZR99OKl2m0GBHpLL4MtVuMErRbwm4v0o5G4jFDrSYT +cz/ejwkAJt74U5d4fIi+cqMZi5aJ8RTqIZ6MyuhbJj/4Iz+OBwax7cmQHwBb7xm0k StCKw01BOzCMC9zFzC4OrJ0GOvQUsWP4e9xCdYkE= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730727AbgCaPe4 (ORCPT ); Tue, 31 Mar 2020 11:34:56 -0400 Received: from mail-wr1-f66.google.com ([209.85.221.66]:37092 "EHLO mail-wr1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727703AbgCaPe4 (ORCPT ); Tue, 31 Mar 2020 11:34:56 -0400 Received: by mail-wr1-f66.google.com with SMTP id w10so26622397wrm.4; Tue, 31 Mar 2020 08:34:55 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=XWJpdT6ZsPCOgPe98UycjXxzkHnMVRDPn15M3ka7UM4=; b=hJC3ikGApOoNVaBpATr/c//jIQhLRz3dLmRCnVFYqgu7FVyS4YiJFeY62OsWo98YJf A4tyFC8wI3jBcskCdWZ2/Z7JugjIHs+eUtP5Bw7/ncHtzt9URqUV5meF+FPm/aa/S5NO MqTOTWYKHjyvHuqwwaiiftNpLM1SElthOXOnGYJqbDC9iP/9zN93qYW+M2ErLeFj4g2J itVhMdbWmMWWRbi4JpkxRjXO+66ZaAG7tKkU63yUERCiTq4y2IWhPP5i7F4OBmyxgU62 c+PE/qSixFr7JqWiQdVjKJg2V03O+cbxZ6ZcP2hfqgEc+8oxnVW/L+c2VAWNbI4Sxdw1 0PvQ== X-Gm-Message-State: ANhLgQ3NFqv3xDGP8WlyLgVhPuCIuh06Pc5Nl/HD7zvMoxHRbhZZs23D zyl2Y0p+xWzhLlmwx3lENWA= X-Google-Smtp-Source: ADFU+vtOC9s0hgunzjXryLDkoY30klCWAusuNW8kiJdYJ6kgbFjbK79bnAt6gZ6I6SlD2xgVK1GhVQ== X-Received: by 2002:adf:ef08:: with SMTP id e8mr22284875wro.66.1585668894424; Tue, 31 Mar 2020 08:34:54 -0700 (PDT) Received: from localhost (ip-37-188-180-223.eurotel.cz. [37.188.180.223]) by smtp.gmail.com with ESMTPSA id o16sm24444126wrw.75.2020.03.31.08.34.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 31 Mar 2020 08:34:53 -0700 (PDT) Date: Tue, 31 Mar 2020 17:34:50 +0200 From: Michal Hocko To: Joel Fernandes Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, rcu@vger.kernel.org, willy@infradead.org, peterz@infradead.org, neilb@suse.com, vbabka@suse.cz, mgorman@suse.de, Andrew Morton , Josh Triplett , Lai Jiangshan , Mathieu Desnoyers , "Paul E. McKenney" , Steven Rostedt Subject: Re: [PATCH RFC] rcu/tree: Use GFP_MEMALLOC for alloc memory to free memory pattern Message-ID: <20200331153450.GM30449@dhcp22.suse.cz> References: <20200331131628.153118-1-joel@joelfernandes.org> <20200331145806.GB236678@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200331145806.GB236678@google.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 31-03-20 10:58:06, Joel Fernandes wrote: [...] > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > > index 4be763355c9fb..965deefffdd58 100644 > > --- a/kernel/rcu/tree.c > > +++ b/kernel/rcu/tree.c > > @@ -3149,7 +3149,7 @@ static inline struct rcu_head *attach_rcu_head_to_object(void *obj) > > > > if (!ptr) > > ptr = kmalloc(sizeof(unsigned long *) + > > - sizeof(struct rcu_head), GFP_ATOMIC | __GFP_NOWARN); > > + sizeof(struct rcu_head), GFP_MEMALLOC); > > Just to add, the main requirements here are: > 1. Allocation should be bounded in time. > 2. Allocation should try hard (possibly tapping into reserves) > 3. Sleeping is Ok but should not affect the time bound. __GFP_ATOMIC | __GFP_HIGH is the way to get an additional access to memory reserves regarless of the sleeping status. Using __GFP_MEMALLOC is quite dangerous because it can deplete _all_ the memory. What does prevent the above code path to do that? If a partial access to reserves is sufficient then why the existing modifiers (mentioned above are not sufficient? -- Michal Hocko SUSE Labs