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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 CD4E1C433E6 for ; Wed, 13 Jan 2021 12:04:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 906A9233FB for ; Wed, 13 Jan 2021 12:04:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726964AbhAMMEJ (ORCPT ); Wed, 13 Jan 2021 07:04:09 -0500 Received: from mx2.suse.de ([195.135.220.15]:34892 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726459AbhAMMEI (ORCPT ); Wed, 13 Jan 2021 07:04:08 -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=1610539402; 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=12ieSSfl0b2FyOCtz8cA53D36htolHYLrszhHSjuYYc=; b=NE4Epht7NIj2h4xRVr+aSXAdG95nDCqZh3OKJYJYcuaeGDSVQc5LEktrafZYEqu1p62/yy Z/2F9sZe+8YhQjr7QW2CkV2hlsV0kjJVZkORNyyNxI/YHcCqFvnKOyFJ/1dGJycYn9WaH/ iRIyO0g0vsRVbnSVkzDSJkv7updxo64= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 79F74AB92; Wed, 13 Jan 2021 12:03:22 +0000 (UTC) Date: Wed, 13 Jan 2021 13:03:20 +0100 From: Michal Hocko To: Muchun Song Cc: Oscar Salvador , Mike Kravetz , Andrew Morton , Naoya Horiguchi , Andi Kleen , Linux Memory Management List , LKML Subject: Re: [External] Re: [PATCH v4 4/6] mm: hugetlb: retry dissolve page when hitting race Message-ID: <20210113120320.GY22493@dhcp22.suse.cz> References: <20210113052209.75531-1-songmuchun@bytedance.com> <20210113052209.75531-5-songmuchun@bytedance.com> <20210113093331.GV22493@dhcp22.suse.cz> <20210113103836.GW22493@dhcp22.suse.cz> <20210113111449.GA26873@linux> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 13-01-21 19:20:17, Muchun Song wrote: > On Wed, Jan 13, 2021 at 7:15 PM Oscar Salvador wrote: > > > > On Wed, Jan 13, 2021 at 07:11:06PM +0800, Muchun Song wrote: > > > If there is no task to be scheduled. Here is just a while loop. > > > The cpu_relax is a good thing to insert into busy-wait loops, > > > right? > > > > But if the race window is that small, does it make sense? > > Actually, there is one exception. The race window could > become larger. If the page is freed via a workqueue (see > free_huge_page()). In this case, the cpu_relax() can > make sense. Right? The system would have to be under serious stress for WQ to clog. I do not expect there would be nothing runable at that stage. Possible? Maybe but if that matters than a short sleep would be more preferable than cpu_relax. -- Michal Hocko SUSE Labs