From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1752397AbeCURpS (ORCPT <rfc822;w@1wt.eu>);
        Wed, 21 Mar 2018 13:45:18 -0400
Received: from userp2120.oracle.com ([156.151.31.85]:51124 "EHLO
        userp2120.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1751699AbeCURpO (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Wed, 21 Mar 2018 13:45:14 -0400
Subject: Re: [RFC PATCH v2 0/4] Eliminate zone->lock contention for
 will-it-scale/page_fault1 and parallel free
To: Aaron Lu <aaron.lu@intel.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, Vlastimil Babka <vbabka@suse.cz>
Cc: Andrew Morton <akpm@linux-foundation.org>,
        Huang Ying <ying.huang@intel.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Kemi Wang <kemi.wang@intel.com>, Tim Chen <tim.c.chen@linux.intel.com>,
        Andi Kleen <ak@linux.intel.com>, Michal Hocko <mhocko@suse.com>,
        Mel Gorman <mgorman@techsingularity.net>,
        Matthew Wilcox <willy@infradead.org>
References: <20180320085452.24641-1-aaron.lu@intel.com>
From: Daniel Jordan <daniel.m.jordan@oracle.com>
Message-ID: <1dfd4b33-6eff-160e-52fd-994d9bcbffed@oracle.com>
Date: Wed, 21 Mar 2018 13:44:25 -0400
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101
 Thunderbird/52.6.0
MIME-Version: 1.0
In-Reply-To: <20180320085452.24641-1-aaron.lu@intel.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 7bit
X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=8839 signatures=668695
X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=2 malwarescore=0
 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=999
 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1
 engine=8.0.1-1711220000 definitions=main-1803200127
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On 03/20/2018 04:54 AM, Aaron Lu wrote:
...snip...
> reduced zone->lock contention on free path from 35% to 1.1%. Also, it
> shows good result on parallel free(*) workload by reducing zone->lock
> contention from 90% to almost zero(lru lock increased from almost 0 to
> 90% though).

Hi Aaron, I'm looking through your series now.  Just wanted to mention that I'm seeing the same interaction between zone->lock and lru_lock in my own testing.  IOW, it's not enough to fix just one or the other: both need attention to get good performance on a big system, at least in this microbenchmark we've both been using.

There's anti-scaling at high core counts where overall system page faults per second actually decrease with more CPUs added to the test.  This happens when either zone->lock or lru_lock contention are completely removed, but the anti-scaling goes away when both locks are fixed.

Anyway, I'll post some actual data on this stuff soon.