linux-kernel - Re: [RFC PATCH v2 0/4] Eliminate zone->lock contention for will-it-scale/page

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Date:   Wed, 21 Mar 2018 13:44:25 -0400
From:   Daniel Jordan <daniel.m.jordan@...cle.com>
To:     Aaron Lu <aaron.lu@...el.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Vlastimil Babka <vbabka@...e.cz>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Huang Ying <ying.huang@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Kemi Wang <kemi.wang@...el.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Michal Hocko <mhocko@...e.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [RFC PATCH v2 0/4] Eliminate zone->lock contention for
 will-it-scale/page_fault1 and parallel free

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.