Re: [PATCH] mm: vmstat: Use zeroed stats for unpopulated zones

[Michal Hocko <mhocko@suse.com>]

On Wed 06-05-20 15:33:36, Vlastimil Babka wrote:
> On 5/4/20 12:26 PM, Michal Hocko wrote:
> > On Mon 04-05-20 12:33:04, Sandipan Das wrote:
> >> For unpopulated zones, the pagesets point to the common
> >> boot_pageset which can have non-zero vm_numa_stat counts.
> >> Because of this memory-less nodes end up having non-zero
> >> NUMA statistics. This can be observed on any architecture
> >> that supports memory-less NUMA nodes.
> >> 
> >> E.g.
> >> 
> >>   $ numactl -H
> >>   available: 2 nodes (0-1)
> >>   node 0 cpus: 0 1 2 3
> >>   node 0 size: 0 MB
> >>   node 0 free: 0 MB
> >>   node 1 cpus: 4 5 6 7
> >>   node 1 size: 8131 MB
> >>   node 1 free: 6980 MB
> >>   node distances:
> >>   node   0   1
> >>     0:  10  40
> >>     1:  40  10
> >> 
> >>   $ numastat
> >>                              node0           node1
> >>   numa_hit                     108           56495
> >>   numa_miss                      0               0
> >>   numa_foreign                   0               0
> >>   interleave_hit                 0            4537
> >>   local_node                   108           31547
> >>   other_node                     0           24948
> >> 
> >> Hence, return zero explicitly for all the stats of an
> >> unpopulated zone.
> > 
> > I hope I am not just confused but I would expect that at least
> > numa_foreign and other_node to be non zero.
> Hmm, checking zone_statistics():
> 
> NUMA_FOREIGN increment uses preferred zone, which is the first in zone in
> zonelist, so it will be a zone from node 1 even for allocations on cpu
> associated to node 0 - assuming node 0's unpopulated zones are not included in
> node 0's zonelist.

But the allocation could have been requested for node 0 regardless of
the amount of memory the node has.
 
> NUMA_OTHER uses numa_node_id(), which would mean the node 0's cpus have node 1
> in their numa_node_id() ? Is that correct?

numa_node_id should reflect the real node the CPU is associated with.
-- 
Michal Hocko
SUSE Labs