Re: [PATCH 4/4] lib/show_mem.c: teach show_mem to work with the given nodemask

[Michal Hocko <mhocko@suse.com>]

On Fri 13-01-17 14:08:34, Vlastimil Babka wrote:
> On 01/12/2017 02:16 PM, Michal Hocko wrote:
> > From: Michal Hocko <mhocko@suse.com>
> > 
> > show_mem() allows to filter out node specific data which is irrelevant
> > to the allocation request via SHOW_MEM_FILTER_NODES. The filtering
> > is done in skip_free_areas_node which skips all nodes which are not
> > in the mems_allowed of the current process. This works most of the
> > time as expected because the nodemask shouldn't be outside of the
> > allocating task but there are some exceptions. E.g. memory hotplug might
> > want to request allocations from outside of the allowed nodes (see
> > new_node_page).
> 
> Hm AFAICS memory hotplug's new_node_page() is restricted both by cpusets (by
> using GFP_USER), and by the nodemask it constructs. That's probably a bug in
> itself, as it shouldn't matter which task is triggering the offline?

yes that is true. A task bound to a node which is offlined would be
funny...

> Which probably means that if show_mem() wants to be really precise, it would
> have to start from nodemask and intersect with cpuset when the allocation in
> question cannot escape it. But if we accept that it's ok when we print too
> many nodes (because we can filter them out when reading the output by having
> also nodemask and mems_allowed printed), and strive only to not miss any
> nodes, then this patch could really fix cases when we do miss (although
> new_node_page() currently isn't such example).

I guess it should be sufficient to add cpuset_print_current_mems_allowed()
in warn_alloc. This should give us the full picture without doing too
much twiddling. What do you think?

-- 
Michal Hocko
SUSE Labs

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