linux-kernel - Re: [PATCH v4 2/3] mm/free_pcppages_bulk: do not hold lock when picking pages to free

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20180302071533.GA6356@intel.com>
Date:   Fri, 2 Mar 2018 15:15:34 +0800
From:   Aaron Lu <aaron.lu@...el.com>
To:     Michal Hocko <mhocko@...nel.org>
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@...el.com>,
        Kemi Wang <kemi.wang@...el.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Matthew Wilcox <willy@...radead.org>,
        David Rientjes <rientjes@...gle.com>
Subject: Re: [PATCH v4 2/3] mm/free_pcppages_bulk: do not hold lock when
 picking pages to free

On Thu, Mar 01, 2018 at 02:55:18PM +0100, Michal Hocko wrote:
> On Thu 01-03-18 14:28:44, Aaron Lu wrote:
> > When freeing a batch of pages from Per-CPU-Pages(PCP) back to buddy,
> > the zone->lock is held and then pages are chosen from PCP's migratetype
> > list. While there is actually no need to do this 'choose part' under
> > lock since it's PCP pages, the only CPU that can touch them is us and
> > irq is also disabled.
> > 
> > Moving this part outside could reduce lock held time and improve
> > performance. Test with will-it-scale/page_fault1 full load:
> > 
> > kernel      Broadwell(2S)  Skylake(2S)   Broadwell(4S)  Skylake(4S)
> > v4.16-rc2+  9034215        7971818       13667135       15677465
> > this patch  9536374 +5.6%  8314710 +4.3% 14070408 +3.0% 16675866 +6.4%
> > 
> > What the test does is: starts $nr_cpu processes and each will repeatedly
> > do the following for 5 minutes:
> > 1 mmap 128M anonymouse space;
> > 2 write access to that space;
> > 3 munmap.
> > The score is the aggregated iteration.
> 
> Iteration count I assume.

Correct.

> I am still quite surprised that this would have such a large impact.

Most likely due to the cachelines for these page structures are warmed
up outside of zone->lock.