1 files changed, 38 insertions, 2 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index c313afcc8e5..a712fb9e04c 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -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