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 D14D3C433E9 for ; Wed, 13 Jan 2021 12:03:29 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 4F4BD233FA for ; Wed, 13 Jan 2021 12:03:28 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4F4BD233FA Authentication-Results: mail.kernel.org; dmarc=fail (p=quarantine dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 2B81D8D0047; Wed, 13 Jan 2021 07:03:28 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 242488D002E; Wed, 13 Jan 2021 07:03:28 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 10A5C8D0047; Wed, 13 Jan 2021 07:03:28 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0234.hostedemail.com [216.40.44.234]) by kanga.kvack.org (Postfix) with ESMTP id EA50A8D002E for ; Wed, 13 Jan 2021 07:03:27 -0500 (EST) Received: from smtpin21.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 7E761362D for ; Wed, 13 Jan 2021 12:03:24 +0000 (UTC) X-FDA: 77700616728.21.rule85_3d11dd12751d Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin21.hostedemail.com (Postfix) with ESMTP id 34F2018045D14 for ; Wed, 13 Jan 2021 12:03:24 +0000 (UTC) X-HE-Tag: rule85_3d11dd12751d X-Filterd-Recvd-Size: 2945 Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf17.hostedemail.com (Postfix) with ESMTP for ; Wed, 13 Jan 2021 12:03:23 +0000 (UTC) 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: X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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