Page allocator: clean up pcp draining functions

- Add comments explaing how drain_pages() works.

- Eliminate useless functions

- Rename drain_all_local_pages to drain_all_pages(). It does drain
  all pages not only those of the local processor.

- Eliminate useless interrupt off / on sequences. drain_pages()
  disables interrupts on its own. The execution thread is
  pinned to processor by the caller. So there is no need to
  disable interrupts.

- Put drain_all_pages() declaration in gfp.h and remove the
  declarations from suspend.h and from mm/memory_hotplug.c

- Make software suspend call drain_all_pages(). The draining
  of processor local pages is may not the right approach if
  software suspend wants to support SMP. If they call drain_all_pages
  then we can make drain_pages() static.

[akpm@linux-foundation.org: fix build]
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Acked-by: Mel Gorman <mel@csn.ul.ie>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: Daniel Walker <dwalker@mvista.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 44 insertions, 41 deletions

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 9512a544d044..7469c503580d 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -481,8 +481,6 @@ check_pages_isolated(unsigned long start_pfn, unsigned long end_pfn)
         return offlined;
 }
 
-extern void drain_all_local_pages(void);
-
 int offline_pages(unsigned long start_pfn,
                   unsigned long end_pfn, unsigned long timeout)
 {
@@ -540,7 +538,7 @@ repeat:
                 lru_add_drain_all();
                 flush_scheduled_work();
                 cond_resched();
-                drain_all_local_pages();
+                drain_all_pages();
         }
 
         pfn = scan_lru_pages(start_pfn, end_pfn);
@@ -563,7 +561,7 @@ repeat:
         flush_scheduled_work();
         yield();
         /* drain pcp pages , this is synchrouns. */
-        drain_all_local_pages();
+        drain_all_pages();
         /* check again */
         offlined_pages = check_pages_isolated(start_pfn, end_pfn);
         if (offlined_pages < 0) {
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index b2838c24e582..5c7de8e959fc 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -890,7 +890,14 @@ void drain_zone_pages(struct zone *zone, struct per_cpu_pages *pcp)
 }
 #endif
 
-static void __drain_pages(unsigned int cpu)
+/*
+ * Drain pages of the indicated processor.
+ *
+ * The processor must either be the current processor and the
+ * thread pinned to the current processor or a processor that
+ * is not online.
+ */
+static void drain_pages(unsigned int cpu)
 {
         unsigned long flags;
         struct zone *zone;
@@ -915,6 +922,22 @@ static void __drain_pages(unsigned int cpu)
         }
 }
 
+/*
+ * Spill all of this CPU's per-cpu pages back into the buddy allocator.
+ */
+void drain_local_pages(void *arg)
+{
+        drain_pages(smp_processor_id());
+}
+
+/*
+ * Spill all the per-cpu pages from all CPUs back into the buddy allocator
+ */
+void drain_all_pages(void)
+{
+        on_each_cpu(drain_local_pages, NULL, 0, 1);
+}
+
 #ifdef CONFIG_HIBERNATION
 
 void mark_free_pages(struct zone *zone)
@@ -952,37 +975,6 @@ void mark_free_pages(struct zone *zone)
 #endif /* CONFIG_PM */
 
 /*
- * Spill all of this CPU's per-cpu pages back into the buddy allocator.
- */
-void drain_local_pages(void)
-{
-        unsigned long flags;
-
-        local_irq_save(flags);  
-        __drain_pages(smp_processor_id());
-        local_irq_restore(flags);       
-}
-
-void smp_drain_local_pages(void *arg)
-{
-        drain_local_pages();
-}
-
-/*
- * Spill all the per-cpu pages from all CPUs back into the buddy allocator
- */
-void drain_all_local_pages(void)
-{
-        unsigned long flags;
-
-        local_irq_save(flags);
-        __drain_pages(smp_processor_id());
-        local_irq_restore(flags);
-
-        smp_call_function(smp_drain_local_pages, NULL, 0, 1);
-}
-
-/*
  * Free a 0-order page
  */
 static void fastcall free_hot_cold_page(struct page *page, int cold)
@@ -1569,7 +1561,7 @@ nofail_alloc:
         cond_resched();
 
         if (order != 0)
-                drain_all_local_pages();
+                drain_all_pages();
 
         if (likely(did_some_progress)) {
                 page = get_page_from_freelist(gfp_mask, order,
@@ -3978,10 +3970,23 @@ static int page_alloc_cpu_notify(struct notifier_block *self,
         int cpu = (unsigned long)hcpu;
 
         if (action == CPU_DEAD || action == CPU_DEAD_FROZEN) {
-                local_irq_disable();
-                __drain_pages(cpu);
+                drain_pages(cpu);
+
+                /*
+                 * Spill the event counters of the dead processor
+                 * into the current processors event counters.
+                 * This artificially elevates the count of the current
+                 * processor.
+                 */
                 vm_events_fold_cpu(cpu);
-                local_irq_enable();
+
+                /*
+                 * Zero the differential counters of the dead processor
+                 * so that the vm statistics are consistent.
+                 *
+                 * This is only okay since the processor is dead and cannot
+                 * race with what we are doing.
+                 */
                 refresh_cpu_vm_stats(cpu);
         }
         return NOTIFY_OK;
@@ -4480,7 +4485,7 @@ int set_migratetype_isolate(struct page *page)
 out:
         spin_unlock_irqrestore(&zone->lock, flags);
         if (!ret)
-                drain_all_local_pages();
+                drain_all_pages();
         return ret;
 }