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=-8.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 6012CC47425 for ; Wed, 30 Sep 2020 13:40:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 240BA20754 for ; Wed, 30 Sep 2020 13:40:03 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="raxd4XYf" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730228AbgI3NkB (ORCPT ); Wed, 30 Sep 2020 09:40:01 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53626 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728149AbgI3NkB (ORCPT ); Wed, 30 Sep 2020 09:40:01 -0400 Received: from mail-lf1-x144.google.com (mail-lf1-x144.google.com [IPv6:2a00:1450:4864:20::144]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7B524C061755; Wed, 30 Sep 2020 06:39:59 -0700 (PDT) Received: by mail-lf1-x144.google.com with SMTP id b12so2180804lfp.9; Wed, 30 Sep 2020 06:39:59 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:date:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=+Mv19Yx2WxdVyKnvOoeq4MvA7Ro0O7JtMWzZ1C2BvJM=; b=raxd4XYfV1muIM8s1gC3S4KP6FGX4R8WUQZ931rlO563LUJMZe0ngCrSQj8u+0ZADi xcySPT1dn0Kv7o5yhplz5jyVOmYihDRuYWtkIk15ar64efQV9oJs5qQDG4nF9hRmomsr iWADp/1No+P3ScB3qO2QO3pfdSsP3Psxr2/Ke6J7uDJRCW8r/N7WHb9KEu5RiSYc5MTg VaedPCasIVN4WBjc+oH89m15UtJwVbAZJb9YCNTc9Q1yueLUJ9+7E39t69GJZoa8izSL /HRUBA0dLo1qWMxyr0zPxHnn7NoLRxAwhsUJesKnOB5oqvIq+/PrUHZR2DjG4tv3egm/ auIA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:date:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=+Mv19Yx2WxdVyKnvOoeq4MvA7Ro0O7JtMWzZ1C2BvJM=; b=qp+lLFOUHy0juBwMSHo3w4fpYiwDSR/qJhnO74/UgaUCsFOB/lUn83bNzPFxhcoZgn VcqSD+QeKfsUpyyqbf4qvZbM+Otfcl1YZ6z1zCjfBysSpvsobqlIgTyjYPDuzQRvce5U qhc8D9yA2ult7h0acy2Y170JRfn2x1maYL8DmHT6MXk1Sr0rWFyKSSZbrwvgb1UjlJad K8yGrQRiu1gHMgBP8eTv/xD5dLnv4R/+3+5BHI5TlVC1UTd9ib0eXURPMl15AVfQ3LHp 3m4ATmkxDrIdKdYWJCD4LUUZxTDhWtG4FT22NDgQJfAgugC8NSI11rTPGbGpLCUpwnZ9 rJ1A== X-Gm-Message-State: AOAM532XpWfcA2VDR2++go29uuq57OE0lkO1AgmhnalSvJ8dCRhHGgT3 9fZIuoQz+lH3E7MswDgzqio= X-Google-Smtp-Source: ABdhPJxpXr0wR69XUTokZpdN0EtefxY7Z63IScx35mYhulRHzMUV81dz8LoZI8BQHtdeOLiUtzgv4g== X-Received: by 2002:ac2:48b2:: with SMTP id u18mr833353lfg.185.1601473197790; Wed, 30 Sep 2020 06:39:57 -0700 (PDT) Received: from pc636 (h5ef52e31.seluork.dyn.perspektivbredband.net. [94.245.46.49]) by smtp.gmail.com with ESMTPSA id a73sm196493lfd.245.2020.09.30.06.39.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 30 Sep 2020 06:39:57 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Wed, 30 Sep 2020 15:39:54 +0200 To: Michal Hocko Cc: Uladzislau Rezki , Mel Gorman , "Paul E. McKenney" , LKML , RCU , linux-mm@kvack.org, Andrew Morton , Peter Zijlstra , Vlastimil Babka , Thomas Gleixner , "Theodore Y . Ts'o" , Joel Fernandes , Sebastian Andrzej Siewior , Oleksiy Avramchenko , Mel Gorman Subject: Re: [RFC-PATCH 2/4] mm: Add __rcu_alloc_page_lockless() func. Message-ID: <20200930133954.GA19235@pc636> References: <20200923154105.GO29330@paulmck-ThinkPad-P72> <20200923232251.GK3179@techsingularity.net> <20200924081614.GA14819@pc636> <20200925080503.GC3389@dhcp22.suse.cz> <20200925153129.GB25350@pc636> <20200925154741.GI3389@dhcp22.suse.cz> <20200929162514.GA8768@pc636> <20200930092732.GP2277@dhcp22.suse.cz> <20200930123535.GB18005@pc636> <20200930124413.GU2277@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200930124413.GU2277@dhcp22.suse.cz> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Sep 30, 2020 at 02:44:13PM +0200, Michal Hocko wrote: > On Wed 30-09-20 14:35:35, Uladzislau Rezki wrote: > > On Wed, Sep 30, 2020 at 11:27:32AM +0200, Michal Hocko wrote: > > > On Tue 29-09-20 18:25:14, Uladzislau Rezki wrote: > > > > > > I look at it in scope of GFP_ATOMIC/GFP_NOWAIT issues, i.e. inability > > > > > > to provide a memory service for contexts which are not allowed to > > > > > > sleep, RCU is part of them. Both flags used to provide such ability > > > > > > before but not anymore. > > > > > > > > > > > > Do you agree with it? > > > > > > > > > > Yes this sucks. But this is something that we likely really want to live > > > > > with. We have to explicitly _document_ that really atomic contexts in RT > > > > > cannot use the allocator. From the past discussions we've had this is > > > > > likely the most reasonable way forward because we do not really want to > > > > > encourage anybody to do something like that and there should be ways > > > > > around that. The same is btw. true also for !RT. The allocator is not > > > > > NMI safe and while we should be able to make it compatible I am not > > > > > convinced we really want to. > > > > > > > > > > Would something like this be helpful wrt documentation? > > > > > > > > > > diff --git a/include/linux/gfp.h b/include/linux/gfp.h > > > > > index 67a0774e080b..9fcd47606493 100644 > > > > > --- a/include/linux/gfp.h > > > > > +++ b/include/linux/gfp.h > > > > > @@ -238,7 +238,9 @@ struct vm_area_struct; > > > > > * %__GFP_FOO flags as necessary. > > > > > * > > > > > * %GFP_ATOMIC users can not sleep and need the allocation to succeed. A lower > > > > > - * watermark is applied to allow access to "atomic reserves" > > > > > + * watermark is applied to allow access to "atomic reserves". > > > > > + * The current implementation doesn't support NMI and other non-preemptive context > > > > > + * (e.g. raw_spin_lock). > > > > > * > > > > > * %GFP_KERNEL is typical for kernel-internal allocations. The caller requires > > > > > * %ZONE_NORMAL or a lower zone for direct access but can direct reclaim. > > > > > > > > > To me it is clear. But also above conflicting statement: > > > > > > > > > > > > %GFP_ATOMIC users can not sleep and need the allocation to succeed. A %lower > > > > > > > > > > > > should be rephrased, IMHO. > > > > > > Any suggestions? Or more specifics about which part is conflicting? It > > > tries to say that there is a higher demand to succeed even though the > > > context cannot sleep to take active measures to achieve that. So the > > > only way to achieve that is to break the watermakrs to a certain degree > > > which is making them more "higher class" than other allocations. > > > > > Michal, i had only one concern about it. It says that %GFP_ATOMIC users > > can not sleep, i.e. callers know that they are in atomic, thus no any > > sleeping, but the chose they make will force them to sleep. > > I am not sure I follow you here. Do you mean they will be forced to > sleep with PREEMPT_RT? > Exactly :) -- Vlad Rezki