On 01/12/2017 02:16 PM, Michal Hocko wrote:
From: Michal Hocko <mhocko@xxxxxxxx> 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?
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).
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