linux-kernel - Re: [PATCH 2/2] mm, memory_hotplug: remove zone restrictions

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Date:   Thu, 6 Jul 2017 07:16:49 +0800
From:   Wei Yang <richard.weiyang@...il.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Wei Yang <richard.weiyang@...il.com>,
        Linux-MM <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...e.de>, Vlastimil Babka <vbabka@...e.cz>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Reza Arbab <arbab@...ux.vnet.ibm.com>,
        Yasuaki Ishimatsu <yasu.isimatu@...il.com>,
        Xishi Qiu <qiuxishi@...wei.com>,
        Kani Toshimitsu <toshi.kani@....com>, slaoub@...il.com,
        Joonsoo Kim <js1304@...il.com>,
        Daniel Kiper <daniel.kiper@...cle.com>,
        Igor Mammedov <imammedo@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] mm, memory_hotplug: remove zone restrictions

On Fri, Jun 30, 2017 at 01:01:18PM +0200, Michal Hocko wrote:
>On Fri 30-06-17 11:55:45, Michal Hocko wrote:
>> On Fri 30-06-17 17:39:56, Wei Yang wrote:
>> > On Fri, Jun 30, 2017 at 4:39 PM, Michal Hocko <mhocko@...nel.org> wrote:
>> [...]
>> > > yes and to be honest I do not plan to fix it unless somebody has a real
>> > > life usecase for it. Now that we allow explicit onlininig type anywhere
>> > > it seems like a reasonable behavior and this will allow us to remove
>> > > quite some code which is always a good deal wrt longterm maintenance.
>> > >
>> > 
>> > hmm... the statistics displayed in /proc/zoneinfo would be meaningless
>> > for zone_normal and zone_movable.
>> 
>> Why would they be meaningless? Counters will always reflect the actual
>> use - if not then it is a bug. And wrt to zone description what is
>> meaningless about
>> memory34/valid_zones:Normal
>> memory35/valid_zones:Normal Movable
>> memory36/valid_zones:Movable
>> memory37/valid_zones:Movable Normal
>> memory38/valid_zones:Movable Normal
>> memory39/valid_zones:Movable Normal
>> memory40/valid_zones:Normal
>> memory41/valid_zones:Movable
>> 
>> And
>> Node 1, zone   Normal
>>   pages free     65465
>>         min      156
>>         low      221
>>         high     286
>>         spanned  229376
>>         present  65536
>>         managed  65536
>> [...]
>>   start_pfn:           1114112
>> Node 1, zone  Movable
>>   pages free     65443
>>         min      156
>>         low      221
>>         high     286
>>         spanned  196608
>>         present  65536
>>         managed  65536
>> [...]
>>   start_pfn:           1179648
>> 
>> ranges are clearly defined as [start_pfn, start_pfn+managed] and managed
>
>errr, this should be [start_pfn, start_pfn + spanned] of course.
>

The spanned is not adjusted after offline, neither does start_pfn. For example,
even offline all the movable_zone range, we can still see the spanned.

Below is a result with a little changed kernel to show the start_pfn always.
The sequence is:
1. bootup

Node 0, zone  Movable
        spanned  65536
	present  0
	managed  0
  start_pfn:           0

2. online movable 2 continuous memory_blocks

Node 0, zone  Movable
        spanned  65536
	present  65536
	managed  65536
  start_pfn:           1310720

3. offline 2nd memory_blocks

Node 0, zone  Movable
        spanned  65536
	present  32768
	managed  32768
  start_pfn:           1310720

4. offline 1st memory_blocks

Node 0, zone  Movable
        spanned  65536
	present  0
	managed  0
  start_pfn:           1310720

So I am not sure this is still clearly defined?

>> matches the number of onlined pages (256MB).
>
>-- 
>Michal Hocko
>SUSE Labs

-- 
Wei Yang
Help you, Help me

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