From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753099AbdLEX4V (ORCPT ); Tue, 5 Dec 2017 18:56:21 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:48766 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752685AbdLEX4T (ORCPT ); Tue, 5 Dec 2017 18:56:19 -0500 Date: Tue, 5 Dec 2017 15:56:18 -0800 From: Andrew Morton To: Michal Hocko Cc: Waiman Long , Vladimir Davydov , Johannes Weiner , Dave Chinner , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH] list_lru: Prefetch neighboring list entries before acquiring lock Message-Id: <20171205155618.7a3a59751ed49c704210b736@linux-foundation.org> In-Reply-To: <20171205144948.ezgo3xpjeytkq6ua@dhcp22.suse.cz> References: <1511965054-6328-1-git-send-email-longman@redhat.com> <20171205144948.ezgo3xpjeytkq6ua@dhcp22.suse.cz> X-Mailer: Sylpheed 3.4.1 (GTK+ 2.24.23; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 5 Dec 2017 15:49:48 +0100 Michal Hocko wrote: > On Wed 29-11-17 09:17:34, Waiman Long wrote: > > The list_lru_del() function removes the given item from the LRU list. > > The operation looks simple, but it involves writing into the cachelines > > of the two neighboring list entries in order to get the deletion done. > > That can take a while if the cachelines aren't there yet, thus > > prolonging the lock hold time. > > > > To reduce the lock hold time, the cachelines of the two neighboring > > list entries are now prefetched before acquiring the list_lru_node's > > lock. > > > > Using a multi-threaded test program that created a large number > > of dentries and then killed them, the execution time was reduced > > from 38.5s to 36.6s after applying the patch on a 2-socket 36-core > > 72-thread x86-64 system. > > > > Signed-off-by: Waiman Long > > The patch still seems to be in the mmotm tree while it breaks > compilation. At least m32r defconfig complains with > mm/list_lru.c: In function 'list_lru_del': > mm/list_lru.c:141:2: error: implicit declaration of function 'prefetchw' [-Werror=implicit-function-declaration] > prefetchw(item->prev); erp, I forgot to cc Stephen. > It also seems that there is no general agreement in the patch. Andrew, > do you plan to keep it? It's in wait-and-see mode.