From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751856AbeBBKuv (ORCPT ); Fri, 2 Feb 2018 05:50:51 -0500 Received: from mx1.redhat.com ([209.132.183.28]:52248 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751129AbeBBKum (ORCPT ); Fri, 2 Feb 2018 05:50:42 -0500 Subject: Re: [RFC PATCH v1 00/13] lru_lock scalability To: Daniel Jordan , linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: aaron.lu@intel.com, ak@linux.intel.com, akpm@linux-foundation.org, Dave.Dice@oracle.com, dave@stgolabs.net, khandual@linux.vnet.ibm.com, ldufour@linux.vnet.ibm.com, mgorman@suse.de, mhocko@kernel.org, pasha.tatashin@oracle.com, steven.sistare@oracle.com, yossi.lev@oracle.com References: <20180131230413.27653-1-daniel.m.jordan@oracle.com> <6bd1c8a5-c682-a3ce-1f9f-f1f53b4117a9@redhat.com> From: Steven Whitehouse Message-ID: <962e6540-08e5-aca2-2ff9-bcbd9650d962@redhat.com> Date: Fri, 2 Feb 2018 10:50:37 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, On 02/02/18 04:18, Daniel Jordan wrote: > > > On 02/01/2018 10:54 AM, Steven Whitehouse wrote: >> Hi, >> >> >> On 31/01/18 23:04, daniel.m.jordan@oracle.com wrote: >>> lru_lock, a per-node* spinlock that protects an LRU list, is one of the >>> hottest locks in the kernel.  On some workloads on large machines, it >>> shows up at the top of lock_stat. >>> >>> One way to improve lru_lock scalability is to introduce an array of >>> locks, >>> with each lock protecting certain batches of LRU pages. >>> >>>          *ooooooooooo**ooooooooooo**ooooooooooo**oooo ... >>>          |           ||           ||           || >>>           \ batch 1 /  \ batch 2 /  \ batch 3 / >>> >>> In this ASCII depiction of an LRU, a page is represented with either >>> '*' >>> or 'o'.  An asterisk indicates a sentinel page, which is a page at the >>> edge of a batch.  An 'o' indicates a non-sentinel page. >>> >>> To remove a non-sentinel LRU page, only one lock from the array is >>> required.  This allows multiple threads to remove pages from different >>> batches simultaneously.  A sentinel page requires lru_lock in >>> addition to >>> a lock from the array. >>> >>> Full performance numbers appear in the last patch in this series, >>> but this >>> prototype allows a microbenchmark to do up to 28% more page faults per >>> second with 16 or more concurrent processes. >>> >>> This work was developed in collaboration with Steve Sistare. >>> >>> Note: This is an early prototype.  I'm submitting it now to support my >>> request to attend LSF/MM, as well as get early feedback on the >>> idea.  Any >>> comments appreciated. >>> >>> >>> * lru_lock is actually per-memcg, but without memcg's in the picture it >>>    becomes per-node. >> GFS2 has an lru list for glocks, which can be contended under certain >> workloads. Work is still ongoing to figure out exactly why, but this >> looks like it might be a good approach to that issue too. The main >> purpose of GFS2's lru list is to allow shrinking of the glocks under >> memory pressure via the gfs2_scan_glock_lru() function, and it looks >> like this type of approach could be used there to improve the >> scalability, > > Glad to hear that this could help in gfs2 as well. > > Hopefully struct gfs2_glock is less space constrained than struct page > for storing the few bits of metadata that this approach requires. > > Daniel > We obviously want to keep gfs2_glock small, however within reason then yet we can add some additional fields as required. The use case is pretty much a standard LRU list, so items are added and removed, mostly at the active end of the list, and the inactive end of the list is scanned periodically by gfs2_scan_glock_lru() Steve.