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

From: Michal Hocko <mhocko@kernel.org>
To: Wei Yang <richard.weiyang@gmail.com>
Cc: Linux-MM <linux-mm@kvack.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Mel Gorman <mgorman@suse.de>, Vlastimil Babka <vbabka@suse.cz>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Reza Arbab <arbab@linux.vnet.ibm.com>,
	Yasuaki Ishimatsu <yasu.isimatu@gmail.com>,
	Xishi Qiu <qiuxishi@huawei.com>,
	Kani Toshimitsu <toshi.kani@hpe.com>,
	slaoub@gmail.com, Joonsoo Kim <js1304@gmail.com>,
	Daniel Kiper <daniel.kiper@oracle.com>,
	Igor Mammedov <imammedo@redhat.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 2/2] mm, memory_hotplug: remove zone restrictions
Date: Fri, 30 Jun 2017 11:55:45 +0200	[thread overview]
Message-ID: <20170630095545.GF22917@dhcp22.suse.cz> (raw)
In-Reply-To: <CADZGyca1-CzaHoR-==DN4kK_YrwmMVnKvowUv-5M4GQP7ZYubg@mail.gmail.com>

On Fri 30-06-17 17:39:56, Wei Yang wrote:
> On Fri, Jun 30, 2017 at 4:39 PM, Michal Hocko <mhocko@kernel.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
matches the number of onlined pages (256MB).
-- 
Michal Hocko
SUSE Labs