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SubjectRe: [PATCH 2/2] mm, memory_hotplug: remove zone restrictions
On Thu 06-07-17 07:16:49, Wei Yang wrote:
> 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@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
> >
> >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.

Which is completely valid. Offline only changes present/managed.

> 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?

Could you be more specific what is not clearly defined? You have
offlined all online memory blocks so present/managed is 0 while the
spanned is unchanged because the zone is still defined in range
[1310720, 1376256].

I also do not see how this is related with the discussed patch as there
is no zone interleaving involved.
--
Michal Hocko
SUSE Labs

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