mm: only IPI CPUs to drain local pages if they exist
[~shefty/rdma-dev.git] / mm / page_alloc.c
index c313afcc8e5aeb52e7b142cfcd7e00d3b595a563..a712fb9e04ce4c6914c34b4a80f5526c7b49f346 100644 (file)
@@ -1161,11 +1161,47 @@ void drain_local_pages(void *arg)
 }
 
 /*
- * Spill all the per-cpu pages from all CPUs back into the buddy allocator
+ * Spill all the per-cpu pages from all CPUs back into the buddy allocator.
+ *
+ * Note that this code is protected against sending an IPI to an offline
+ * CPU but does not guarantee sending an IPI to newly hotplugged CPUs:
+ * on_each_cpu_mask() blocks hotplug and won't talk to offlined CPUs but
+ * nothing keeps CPUs from showing up after we populated the cpumask and
+ * before the call to on_each_cpu_mask().
  */
 void drain_all_pages(void)
 {
-       on_each_cpu(drain_local_pages, NULL, 1);
+       int cpu;
+       struct per_cpu_pageset *pcp;
+       struct zone *zone;
+
+       /*
+        * Allocate in the BSS so we wont require allocation in
+        * direct reclaim path for CONFIG_CPUMASK_OFFSTACK=y
+        */
+       static cpumask_t cpus_with_pcps;
+
+       /*
+        * We don't care about racing with CPU hotplug event
+        * as offline notification will cause the notified
+        * cpu to drain that CPU pcps and on_each_cpu_mask
+        * disables preemption as part of its processing
+        */
+       for_each_online_cpu(cpu) {
+               bool has_pcps = false;
+               for_each_populated_zone(zone) {
+                       pcp = per_cpu_ptr(zone->pageset, cpu);
+                       if (pcp->pcp.count) {
+                               has_pcps = true;
+                               break;
+                       }
+               }
+               if (has_pcps)
+                       cpumask_set_cpu(cpu, &cpus_with_pcps);
+               else
+                       cpumask_clear_cpu(cpu, &cpus_with_pcps);
+       }
+       on_each_cpu_mask(&cpus_with_pcps, drain_local_pages, NULL, 1);
 }
 
 #ifdef CONFIG_HIBERNATION