linux-kernel - Re: [PATCH RESEND] autonuma: Fix scan period updating

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Date:   Mon, 29 Jul 2019 11:04:58 +0800
From:   "Huang\, Ying" <ying.huang@...el.com>
To:     Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>, Rik van Riel <riel@...hat.com>,
        Mel Gorman <mgorman@...e.de>, <jhladky@...hat.com>,
        <lvenanci@...hat.com>, Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH RESEND] autonuma: Fix scan period updating

Srikar Dronamraju <srikar@...ux.vnet.ibm.com> writes:

> * Huang, Ying <ying.huang@...el.com> [2019-07-26 15:45:39]:
>
>> Hi, Srikar,
>> 
>> >
>> > More Remote + Private page Accesses:
>> > Most likely the Private accesses are going to be local accesses.
>> >
>> > In the unlikely event of the private accesses not being local, we should
>> > scan faster so that the memory and task consolidates.
>> >
>> > More Remote + Shared page Accesses: This means the workload has not
>> > consolidated and needs to scan faster. So we need to scan faster.
>> 
>> This sounds reasonable.  But
>> 
>> lr_ratio < NUMA_PERIOD_THRESHOLD
>> 
>> doesn't indicate More Remote.  If Local = Remote, it is also true.  If
>
> less lr_ratio means more remote.
>
>> there are also more Shared, we should slow down the scanning.  So, the
>
> Why should we slowing down if there are more remote shared accesses?
>
>> logic could be
>> 
>> if (lr_ratio >= NUMA_PERIOD_THRESHOLD)
>>     slow down scanning
>> else if (sp_ratio >= NUMA_PERIOD_THRESHOLD) {
>>     if (NUMA_PERIOD_SLOTS - lr_ratio >= NUMA_PERIOD_THRESHOLD)
>>         speed up scanning

Thought about this again.  For example, a multi-threads workload runs on
a 4-sockets machine, and most memory accesses are shared.  The optimal
situation will be pseudo-interleaving, that is, spreading memory
accesses evenly among 4 NUMA nodes.  Where "share" >> "private", and
"remote" > "local".  And we should slow down scanning to reduce the
overhead.

What do you think about this?

Best Regards,
Huang, Ying

>>     else
>>         slow down scanning
>> } else
>>    speed up scanning
>> 
>> This follows your idea better?
>> 
>> Best Regards,
>> Huang, Ying