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

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Date:   Fri, 30 Mar 2018 10:27:24 -0400
From:   Daniel Jordan <daniel.m.jordan@...cle.com>
To:     Aaron Lu <aaron.lu@...el.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        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>,
        Vlastimil Babka <vbabka@...e.cz>,
        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 03/29/2018 09:42 PM, Aaron Lu wrote:
> On Thu, Mar 29, 2018 at 03:19:46PM -0400, Daniel Jordan wrote:
>> On 03/20/2018 04:54 AM, Aaron Lu wrote:
>>> This series is meant to improve zone->lock scalability for order 0 pages.
>>> With will-it-scale/page_fault1 workload, on a 2 sockets Intel Skylake
>>> server with 112 CPUs, CPU spend 80% of its time spinning on zone->lock.
>>> Perf profile shows the most time consuming part under zone->lock is the
>>> cache miss on "struct page", so here I'm trying to avoid those cache
>>> misses.
>>
>> I ran page_fault1 comparing 4.16-rc5 to your recent work, these four patches
>> plus the three others from your github branch zone_lock_rfc_v2. Out of
>> curiosity I also threw in another 4.16-rc5 with the pcp batch size adjusted
>> so high (10922 pages) that we always stay in the pcp lists and out of buddy
>> completely.  I used your patch[*] in this last kernel.
>>
>> This was on a 2-socket, 20-core broadwell server.
>>
>> There were some small regressions a bit outside the noise at low process
>> counts (2-5) but I'm not sure they're repeatable.  Anyway, it does improve
>> the microbenchmark across the board.
> 
> Thanks for the result.
> 
> The limited improvement is expected since lock contention only shifts,
> not entirely gone. So what is interesting to see is how it performs with
> v4.16-rc5 + my_zone_lock_patchset + your_lru_lock_patchset

Yep, that's 'coming soon.'