[Xen-devel] [PATCH v3 01/10] page-alloc: Clamp get_free_buddy() to online nodes

[Andrew Cooper <andrew.cooper3@citrix.com>]

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@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
---
CC: Jan Beulich <JBeulich@suse.com>
CC: Wei Liu <wl@xen.org>
CC: Roger Pau Monné <roger.pau@citrix.com>
CC: Stefano Stabellini <sstabellini@kernel.org>
CC: Julien Grall <julien.grall@arm.com>
CC: George Dunlap <george.dunlap@eu.citrix.com>

v3:
 * Rebase to before the nodemask API cleanup, to make it easier to backport.
v2:
 * Rebase over the nodemask API change, and implement with a single
   nodes_and()
---
 xen/common/page_alloc.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
index 44a72d0b19..efa437c7df 100644
--- a/xen/common/page_alloc.c
+++ b/xen/common/page_alloc.c
@@ -811,11 +811,18 @@ 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 = node_online_map;
     unsigned int j, zone, nodemask_retry = 0;
     struct page_info *pg;
     bool use_unscrubbed = (memflags & MEMF_no_scrub);
 
+    /*
+     * d->node_affinity is our preferred allocation set if provided, but it
+     * may have bit set outside of node_online_map.  Clamp it.
+     */
+    if ( d )
+        nodes_and(nodemask, nodemask, d->node_affinity);
+
     if ( node == NUMA_NO_NODE )
     {
         if ( d != NULL )
-- 
2.11.0


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