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 EF291C4727F for ; Wed, 30 Sep 2020 12:35:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A9B712076E for ; Wed, 30 Sep 2020 12:35:43 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="HEj934jm" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729734AbgI3Mfm (ORCPT ); Wed, 30 Sep 2020 08:35:42 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43698 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725776AbgI3Mfm (ORCPT ); Wed, 30 Sep 2020 08:35:42 -0400 Received: from mail-lj1-x244.google.com (mail-lj1-x244.google.com [IPv6:2a00:1450:4864:20::244]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3020DC061755; Wed, 30 Sep 2020 05:35:40 -0700 (PDT) Received: by mail-lj1-x244.google.com with SMTP id r24so1435782ljm.3; Wed, 30 Sep 2020 05:35:40 -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=U0wETEnLdcHAMMRClW16sz0krsjbRfTAZCMrQrsYMPs=; b=HEj934jmRgjFayiqKOLQMdEW/lH+QawuPl6H+620f6thJPaX6zKgwQchmOts8wLO2D DFTaeaViw8zfE6rSmiyaRafnLR/nWnoGQfcUi4KpVqDgsiJML9L6fuZw6NsYrry6F7wh NIDKafCoAQw8O0m7eb7SnrSQGYJ8Pu0xnK7OEszQBLV3wpUtt+Judf61pasPbkOTHsDL 7pXrA7kzfsCAGQ00O0JXZGaH0QXAnF1mfy8H5qai81CiCICsE1Ubc05cCy04qCtn225t GJGC7dnV3LbNZ07dLsJ9JZ5t9qu00t/3a3aNN/Ac+UomHSPYPG46Dw98ZH8sCozxEHqf gWrw== 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=U0wETEnLdcHAMMRClW16sz0krsjbRfTAZCMrQrsYMPs=; b=FWjr7d9uAZBogGXeS3fRHrDvutTqYlSi99X6zYngbARgWWZOp4Scg++2/+2Fk1tdTb +uVtOSXt7RVtd3hr/qqxAI0Ko1u50IBVF8YcJXMlWI3qv0Y17RWmP7m4BQgMD+J1umEA A8CN3YLldgSBrIfjKieEip9tUWVGMVox+p0vo8hiZHSK7cJesg/K96R+efqinVoG3peO /bGezVWOJNZZMYMRL+7AX7qXclu6mPSnx3vG0uTcttwdCRo2oZvv9Y3CPEA5p2lk+JMt glQ+tWXOLNsEfV3O8DBApPVxT/ty8MJKjrf6CLOOieXsDUc1lBLnYwD7d1oOGcz1JonB a5+w== X-Gm-Message-State: AOAM532R926qwGuUTZf8lKr/y7CciBgBdGrsn1N2hlaw1jlJ0Bvx/y15 EaYLNPxEA0egU/36aC6kerEkS+SG0dU7nsIN X-Google-Smtp-Source: ABdhPJy0QVyPoiB83YcLetwpT5bpaqWY6CzScIShcG+T9Tysq+SwA063A/IIQPiKShRgNEr7FP5QZA== X-Received: by 2002:a2e:86c2:: with SMTP id n2mr768495ljj.346.1601469338406; Wed, 30 Sep 2020 05:35:38 -0700 (PDT) Received: from pc636 (h5ef52e31.seluork.dyn.perspektivbredband.net. [94.245.46.49]) by smtp.gmail.com with ESMTPSA id 191sm179011lfa.131.2020.09.30.05.35.37 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 30 Sep 2020 05:35:37 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Wed, 30 Sep 2020 14:35:35 +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: <20200930123535.GB18005@pc636> References: <20200922131257.GA29241@pc636> <20200923103706.GJ3179@techsingularity.net> <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200930092732.GP2277@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 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. -- Vlad Rezki