Initially, the per-cpu pagesets of each zone are set to the boot pagesets.
The real pagesets are allocated later but before that happens, page
allocations do occur and the numa stats for the boot pagesets get
incremented since they are common to all zones at that point.

The real pagesets, however, are allocated for the populated zones only.
Unpopulated zones, like those associated with memory-less nodes, continue
using the boot pageset and end up skewing the numa stats of the
corresponding node.

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, the boot pageset stats need to be cleared after the real pagesets
are allocated.

After this point, the stats of the boot pagesets do not change as page
allocations requested for a memory-less node will either fail (if
__GFP_THISNODE is used) or get fulfilled by a preferred zone of a
different node based on the fallback zonelist.

[sandipan@linux.ibm.com: v3]
  Link: http://lkml.kernel.org/r/20200511170356.162531-1-sandipan@linux.ibm.comSigned-off-by: Sandipan Das <sandipan@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: Michal Hocko <mhocko@suse.com>
Cc: "Kirill A . Shutemov" <kirill@shutemov.name>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Link: http://lkml.kernel.org/r/9c9c2d1b15e37f6e6bf32f99e3100035e90c4ac9.1588868430.git.sandipan@linux.ibm.comSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>