[Xen-devel] [PATCH 3/3] page-alloc: Clamp get_free_buddy() to online nodes

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

d->node_affinity defaults to NODE_MASK_ALL which has bits set outside of
node_online_map.  This in turn causes the loop in get_free_buddy() to waste
effort iterating over offline nodes.

Always clamp d->node_affinity to node_online_map when in use.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
CC: Julien Grall <julien.grall@xxxxxxx>
CC: George Dunlap <george.dunlap@xxxxxxxxxxxxx>

v2:
 * Rebase over the nodemask API change, and implement with a single
   nodes_and()
---
 xen/common/page_alloc.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
index 7bba5b0b2e..fe1159b352 100644
--- a/xen/common/page_alloc.c
+++ b/xen/common/page_alloc.c
@@ -811,11 +811,15 @@ static struct page_info *get_free_buddy(unsigned int 
zone_lo,
                                         const struct domain *d)
 {
     nodeid_t first, node = MEMF_get_node(memflags), req_node = node;
-    nodemask_t nodemask = d ? d->node_affinity : node_online_map;
+    nodemask_t nodemask;
     unsigned int j, zone, nodemask_retry = 0;
     struct page_info *pg;
     bool use_unscrubbed = (memflags & MEMF_no_scrub);
 
+    /* Clamp nodemask to node_online_map and optionally d->node_affinity. */
+    nodes_and(&nodemask, &node_online_map,
+              d ? &d->node_affinity : &node_online_map);
+
     if ( node == NUMA_NO_NODE )
     {
         if ( d != NULL )
-- 
2.11.0


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