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Re: [patch v2] mm, vmstat: print non-populated zones in zoneinfo

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  Re: [patch v2] mm, vmstat: print non-populated zones in zoneinfo Michal Hocko <mhocko@kernel.org> - 2017-03-17 10:00 +0100
    Re: [patch v2] mm, vmstat: print non-populated zones in zoneinfo David Rientjes <rientjes@google.com> - 2017-03-17 22:30 +0100

#1603120 — Re: [patch v2] mm, vmstat: print non-populated zones in zoneinfo

On Wed 08-03-17 15:41:59, Michal Hocko wrote:
> On Fri 03-03-17 14:53:07, David Rientjes wrote:
> > Initscripts can use the information (protection levels) from
> > /proc/zoneinfo to configure vm.lowmem_reserve_ratio at boot.
> > 
> > vm.lowmem_reserve_ratio is an array of ratios for each configured zone on
> > the system.  If a zone is not populated on an arch, /proc/zoneinfo
> > suppresses its output.
> > 
> > This results in there not being a 1:1 mapping between the set of zones
> > emitted by /proc/zoneinfo and the zones configured by
> > vm.lowmem_reserve_ratio.
> >
> > This patch shows statistics for non-populated zones in /proc/zoneinfo.
> > The zones exist and hold a spot in the vm.lowmem_reserve_ratio array.
> > Without this patch, it is not possible to determine which index in the
> > array controls which zone if one or more zones on the system are not
> > populated.
> > 
> > Remaining users of walk_zones_in_node() are unchanged.  Files such as
> > /proc/pagetypeinfo require certain zone data to be initialized properly
> > for display, which is not done for unpopulated zones.
> 
> Does it really make sense to print any counters of that zone though?
> Your follow up patch just suggests that we don't want some but what
> about others?
> 
> I can see how skipping empty zones completely can be clumsy but wouldn't
> it be sufficient to just provide
> 
> Node $NUM, zone $NAME
> (unpopulated)
> 
> instead?

ping
-- 
Michal Hocko
SUSE Labs

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#1603627

On Fri, 17 Mar 2017, Michal Hocko wrote:

> > Does it really make sense to print any counters of that zone though?
> > Your follow up patch just suggests that we don't want some but what
> > about others?
> > 

Managed and present pages needs to be emitted for userspace parsing of 
memory hotplug, I chose not to suppress the five or six other members 
since the risk of breaking existing parsers far outweighs any savings from 
not emitting these lines.  There is already plenty of opportunities to 
clean /proc/zoneinfo up as described by Andrew that may be possible but 
care needs to taken to ensure we don't break existing readers.

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