linux-kernel - Re: [RFC] autonuma: Support to scan page table asynchronously

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Date:   Thu, 16 Apr 2020 09:24:35 +0800
From:   "Huang\, Ying" <ying.huang@...el.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Mel Gorman <mgorman@...hsingularity.net>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...hat.com>,
        Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...riel.com>,
        Daniel Jordan <daniel.m.jordan@...cle.com>,
        Tejun Heo <tj@...nel.org>, Dave Hansen <dave.hansen@...el.com>,
        Tim Chen <tim.c.chen@...el.com>,
        Aubrey Li <aubrey.li@...el.com>
Subject: Re: [RFC] autonuma: Support to scan page table asynchronously

Peter Zijlstra <peterz@...radead.org> writes:

> On Tue, Apr 14, 2020 at 01:06:46PM +0100, Mel Gorman wrote:
>> While it's just an opinion, my preference would be to focus on reducing
>> the cost and amount of scanning done -- particularly for threads.
>
> This; I really don't believe in those back-charging things, esp. since
> not having cgroups or having multiple applications in a single cgroup is
> a valid setup.

Technically, it appears possible to back-charge the CPU time to the
process/thread directly (not the cgroup).

> Another way to reduce latency spikes is to decrease both
> sysctl_numa_balancing_scan_delay and sysctl_numa_balancing_scan_size.
> Then you do more smaller scans. By scanning more often you reduce the
> contrast, by reducing the size you lower the max latency.

Yes.  This can reduce latency spikes.

Best Regards,
Huang, Ying

> And this is all assuming you actually want numa balancing for this
> process.