linux-kernel - Re: [PATCH 3/3] mm: adjust vm_committed_as_batch according to vm overcommit policy

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Message-ID: <20200515083814.GE69177@shbuild999.sh.intel.com>
Date:   Fri, 15 May 2020 16:38:14 +0800
From:   Feng Tang <feng.tang@...el.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Matthew Wilcox <willy@...radead.org>,
        Mel Gorman <mgorman@...e.de>,
        Kees Cook <keescook@...omium.org>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Iurii Zaikin <yzaikin@...gle.com>,
        "Kleen, Andi" <andi.kleen@...el.com>,
        "Chen, Tim C" <tim.c.chen@...el.com>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "Huang, Ying" <ying.huang@...el.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] mm: adjust vm_committed_as_batch according to vm
 overcommit policy

On Fri, May 15, 2020 at 03:44:43PM +0800, Michal Hocko wrote:
> On Fri 08-05-20 15:25:17, Feng Tang wrote:
> > When checking a performance change for will-it-scale scalability
> > mmap test [1], we found very high lock contention for spinlock of
> > percpu counter 'vm_committed_as':
> 
> Btw. you are focusing on a microbenchmark here but I believe that there
> are non-synthetic worklaods which would benefit from a larger batch.
> E.g. large in memory databases which do large mmaps during startups
> from multiple threads.

I imagined cases like this too :) but was not sure there are such cases.
So I only put down the the benchmark I've worked with in 0day.

Thanks,
Feng

> -- 
> Michal Hocko
> SUSE Labs