mm, oom: consider present pages for the node size

constrained_alloc() calculates the size of the oom domain by using
node_spanned_pages which is incorrect because this is the full range of
the physical memory range that the numa node occupies rather than the
memory that backs that range which is represented by node_present_pages.

Sparsely populated nodes (e.g.  after memory hot remove or simply sparse
due to memory layout) can have really a large difference between the two.
This shouldn't really cause any real user observable problems because the
oom calculates a ratio against totalpages and used memory cannot exceed
present pages but it is confusing and wrong from code point of view.

Link: http://lkml.kernel.org/r/20190829163443.899-1-mhocko@kernel.orgSigned-off-by: NMichal Hocko <mhocko@suse.com>
Reported-by: NDavid Hildenbrand <david@redhat.com>
Reviewed-by: NDavid Hildenbrand <david@redhat.com>
Acked-by: NDavid Rientjes <rientjes@google.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/oom_kill.c

@@ -287,7 +287,7 @@ static enum oom_constraint constrained_alloc(struct oom_control *oc)
 	    !nodes_subset(node_states[N_MEMORY], *oc->nodemask)) {
 		oc->totalpages = total_swap_pages;
 		for_each_node_mask(nid, *oc->nodemask)
-			oc->totalpages += node_spanned_pages(nid);
+			oc->totalpages += node_present_pages(nid);
 		return CONSTRAINT_MEMORY_POLICY;
 	}
 
@@ -300,7 +300,7 @@ static enum oom_constraint constrained_alloc(struct oom_control *oc)
 	if (cpuset_limited) {
 		oc->totalpages = total_swap_pages;
 		for_each_node_mask(nid, cpuset_current_mems_allowed)
-			oc->totalpages += node_spanned_pages(nid);
+			oc->totalpages += node_present_pages(nid);
 		return CONSTRAINT_CPUSET;
 	}
 	return CONSTRAINT_NONE;