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=-8.2 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 71D1DC47423 for ; Tue, 29 Sep 2020 16:25:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1272D20936 for ; Tue, 29 Sep 2020 16:25:23 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="ItqoUv/Y" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729463AbgI2QZW (ORCPT ); Tue, 29 Sep 2020 12:25:22 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54910 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728322AbgI2QZV (ORCPT ); Tue, 29 Sep 2020 12:25:21 -0400 Received: from mail-lf1-x143.google.com (mail-lf1-x143.google.com [IPv6:2a00:1450:4864:20::143]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 68C3BC061755; Tue, 29 Sep 2020 09:25:19 -0700 (PDT) Received: by mail-lf1-x143.google.com with SMTP id y11so6247720lfl.5; Tue, 29 Sep 2020 09:25:19 -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=3h7n0kDoWxJUkwhkiM6hwjpaSHbo+Kpn1WLzHzipkyI=; b=ItqoUv/YfW+YGoIsABPqwUCJ3aW66rxag+E/tYt/pr3c9vgOZqoboOPd/5+G+Jta4u VmOds2eutD86AJOuEwpqr14g03ny82jaLNumOm3y12CtvgwLXNhV37zkqa22rhb0QZz8 P58mF/7/sH35NzmpmvuCopz4osPHpHhsA9vTUQiEbr8bljBXd1wkEN5v4ZLd4L2E9etw yl7C2uiqwLjlnYJK8BgFU96NiYrXR74S961ym6CsMYjjHSwIENjqoA+DFtW5aGp1b46U F/CvJksW5nwaNXbW++dT4UPtQzVTtIfSlXUiwrZQd/wJfDYk+dKv0j93mDj+OsjuYmPx yLNw== 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=3h7n0kDoWxJUkwhkiM6hwjpaSHbo+Kpn1WLzHzipkyI=; b=iGtQaSxXlW2Cmn5GtU+US9cW3yWS8+ZeI/2GpMWOfBpKWF+9m5wx5xAcmcBnOBMw5d qeHTZa9gkxLpZth1yvpbKLEbkt4Rp5AhjA6gJoDkDRckKSuEdffm0xk1I7zXSsdoCC6o xaVG+1/ErwJ4MmRu8egLxmzvTk1dYQfbpbNHagN3SAsTueCJC7Ch0QSmy3mqHhszvDlV vntbdB8SzvsMZRoYFyiNeMf3/I/QjREa4XxFoL7cM0Zgo2ZlhpuzxTMS5kY77HKzPxCd XSYVTQNZtq2uXJuDTa+Cyz79LxfDcrKNdMQ48uDVINhvAwkjRhXy0hChdNVjAIJfsKxu 9Tvw== X-Gm-Message-State: AOAM533BSj+iwnyYMv08ApiQr6Es+bUkBLu5uabG5RvmyJrpHRG/s1VH eqnNYw/VdJqGhosl8FXJMFg= X-Google-Smtp-Source: ABdhPJypuHLpBjSrh4x5SAP5mpaT+K/3JmAlFT4O+cw8Pet4vn4FOFS90XV3mVEaMASa+nEvO2elOg== X-Received: by 2002:a19:a93:: with SMTP id 141mr1439631lfk.292.1601396717818; Tue, 29 Sep 2020 09:25:17 -0700 (PDT) Received: from pc636 (h5ef52e31.seluork.dyn.perspektivbredband.net. [94.245.46.49]) by smtp.gmail.com with ESMTPSA id q24sm3289429lfo.149.2020.09.29.09.25.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 29 Sep 2020 09:25:16 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Tue, 29 Sep 2020 18:25:14 +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: <20200929162514.GA8768@pc636> References: <20200921194819.GA24236@pc636> <20200922075002.GU12990@dhcp22.suse.cz> <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200925154741.GI3389@dhcp22.suse.cz> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > > 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. -- Vlad Rezki