linux-kernel - Re: [PATCH v2 3/5] mm: enlarge NUMA counters threshold size

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Date:   Wed, 20 Dec 2017 18:21:40 +0800
From:   kemi <kemi.wang@...el.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Johannes Weiner <hannes@...xchg.org>,
        Christopher Lameter <cl@...ux.com>,
        YASUAKI ISHIMATSU <yasu.isimatu@...il.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Nikolay Borisov <nborisov@...e.com>,
        Pavel Tatashin <pasha.tatashin@...cle.com>,
        David Rientjes <rientjes@...gle.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Dave <dave.hansen@...ux.intel.com>,
        Andi Kleen <andi.kleen@...el.com>,
        Tim Chen <tim.c.chen@...el.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Ying Huang <ying.huang@...el.com>,
        Aaron Lu <aaron.lu@...el.com>, Aubrey Li <aubrey.li@...el.com>,
        Linux MM <linux-mm@...ck.org>,
        Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 3/5] mm: enlarge NUMA counters threshold size



On 2017年12月20日 18:12, Michal Hocko wrote:
> On Wed 20-12-17 13:52:14, kemi wrote:
>>
>>
>> On 2017年12月19日 20:40, Michal Hocko wrote:
>>> On Tue 19-12-17 14:39:24, Kemi Wang wrote:
>>>> We have seen significant overhead in cache bouncing caused by NUMA counters
>>>> update in multi-threaded page allocation. See 'commit 1d90ca897cb0 ("mm:
>>>> update NUMA counter threshold size")' for more details.
>>>>
>>>> This patch updates NUMA counters to a fixed size of (MAX_S16 - 2) and deals
>>>> with global counter update using different threshold size for node page
>>>> stats.
>>>
>>> Again, no numbers.
>>
>> Compare to vanilla kernel, I don't think it has performance improvement, so
>> I didn't post performance data here.
>> But, if you would like to see performance gain from enlarging threshold size
>> for NUMA stats (compare to the first patch), I will do that later. 
> 
> Please do. I would also like to hear _why_ all counters cannot simply
> behave same. In other words why we cannot simply increase
> stat_threshold? Maybe calculate_normal_threshold needs a better scaling
> for larger machines.
> 

Agree. We may consider that.
But, unlike NUMA counters which do not effect system decision.
We need consider very carefully when increase stat_threshold for all the counters
for larger machines. BTW, this is another topic that we may discuss it in different
thread.