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=-10.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 0D17DC433E0 for ; Thu, 11 Mar 2021 08:41:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C456264F87 for ; Thu, 11 Mar 2021 08:41:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231571AbhCKIlP (ORCPT ); Thu, 11 Mar 2021 03:41:15 -0500 Received: from mx2.suse.de ([195.135.220.15]:49810 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231394AbhCKIk7 (ORCPT ); Thu, 11 Mar 2021 03:40:59 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1615452057; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=zPVxzyGzi1aB06Q/yol9xL73rwPJTQl7TL+0Dnc4zDk=; b=Ln1d0WteFwtmFPRyPKUGJPriveauMVO6RTfR9ST8coq7SNjlvpAocx3emNwR9RsoPMUVSK UHpwXPQDIVtkMHd0WgyH5joYmb4O/1UedHeo7Y1mXLAraoS8BKyNSNjgO7hAfZnF8NMIv8 dMZq3mdTcRjaImjbVehFCLmnRomStjQ= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 563BFAB8C; Thu, 11 Mar 2021 08:40:57 +0000 (UTC) Date: Thu, 11 Mar 2021 09:40:54 +0100 From: Michal Hocko To: "Paul E. McKenney" Cc: Mike Kravetz , Muchun Song , corbet@lwn.net, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com, dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org, viro@zeniv.linux.org.uk, akpm@linux-foundation.org, mchehab+huawei@kernel.org, pawan.kumar.gupta@linux.intel.com, rdunlap@infradead.org, oneukum@suse.com, anshuman.khandual@arm.com, jroedel@suse.de, almasrymina@google.com, rientjes@google.com, willy@infradead.org, osalvador@suse.de, song.bao.hua@hisilicon.com, david@redhat.com, naoya.horiguchi@nec.com, joao.m.martins@oracle.com, duanxiongchun@bytedance.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, Chen Huang , Bodeddula Balasubramaniam Subject: Re: [PATCH v18 4/9] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page Message-ID: References: <20210308102807.59745-1-songmuchun@bytedance.com> <20210308102807.59745-5-songmuchun@bytedance.com> <20210310214909.GY2696@paulmck-ThinkPad-P72> <68bc8cc9-a15b-2e97-9a2a-282fe6e9bd3f@oracle.com> <20210310232851.GZ2696@paulmck-ThinkPad-P72> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210310232851.GZ2696@paulmck-ThinkPad-P72> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 10-03-21 15:28:51, Paul E. McKenney wrote: > On Wed, Mar 10, 2021 at 02:10:12PM -0800, Mike Kravetz wrote: > > On 3/10/21 1:49 PM, Paul E. McKenney wrote: > > > On Wed, Mar 10, 2021 at 10:11:22PM +0100, Michal Hocko wrote: > > >> On Wed 10-03-21 10:56:08, Mike Kravetz wrote: > > >>> On 3/10/21 7:19 AM, Michal Hocko wrote: > > >>>> On Mon 08-03-21 18:28:02, Muchun Song wrote: > > >>>> [...] > > >>>>> @@ -1447,7 +1486,7 @@ void free_huge_page(struct page *page) > > >>>>> /* > > >>>>> * Defer freeing if in non-task context to avoid hugetlb_lock deadlock. > > >>>>> */ > > >>>>> - if (!in_task()) { > > >>>>> + if (in_atomic()) { > > >>>> > > >>>> As I've said elsewhere in_atomic doesn't work for CONFIG_PREEMPT_COUNT=n. > > >>>> We need this change for other reasons and so it would be better to pull > > >>>> it out into a separate patch which also makes HUGETLB depend on > > >>>> PREEMPT_COUNT. > > >>> > > >>> Yes, the issue of calling put_page for hugetlb pages from any context > > >>> still needs work. IMO, that is outside the scope of this series. We > > >>> already have code in this path which blocks/sleeps. > > >>> > > >>> Making HUGETLB depend on PREEMPT_COUNT is too restrictive. IIUC, > > >>> PREEMPT_COUNT will only be enabled if we enable: > > >>> PREEMPT "Preemptible Kernel (Low-Latency Desktop)" > > >>> PREEMPT_RT "Fully Preemptible Kernel (Real-Time)" > > >>> or, other 'debug' options. These are not enabled in 'more common' > > >>> kernels. Of course, we do not want to disable HUGETLB in common > > >>> configurations. > > >> > > >> I haven't tried that but PREEMPT_COUNT should be selectable even without > > >> any change to the preemption model (e.g. !PREEMPT). > > > > > > It works reliably for me, for example as in the diff below. So, > > > as Michal says, you should be able to add "select PREEMPT_COUNT" to > > > whatever Kconfig option you need to. > > > > > > > Thanks Paul. > > > > I may have been misreading Michal's suggestion of "make HUGETLB depend on > > PREEMPT_COUNT". We could "select PREEMPT_COUNT" if HUGETLB is enabled. > > However, since HUGETLB is enabled in most configs, then this would > > result in PREEMPT_COUNT also being enabled in most configs. I honestly > > do not know how much this will cost us? I assume that if it was free or > > really cheap it would already be always on? > > There are a -lot- of configs out there, so are you sure that HUGETLB is > really enabled in most of them? ;-) It certainly is enabled for all distribution kernels and many are !PREEMPT so I believe this is what Mike was concerned about. > More seriously, I was going by earlier emails in this and related threads > plus Michal's "PREEMPT_COUNT should be selectable". But there are other > situations that would like PREEMPT_COUNT. And to your point, some who > would rather PREEMPT_COUNT not be universally enabled. I haven't seen > any performance or kernel-size numbers from any of them, however. Yeah per cpu preempt counting shouldn't be noticeable but I have to confess I haven't benchmarked it. -- Michal Hocko SUSE Labs