[RFC][PATCH 7/7][memcg] use spin lock instead of bit_spin_lock in page_cgroup

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

This patch replaces page_cgroup's bit_spinlock with spinlock. In general,
spinlock has good implementation than bit_spin_lock and we should use
it if we have a room for it. In 64bit arch, we have extra 4bytes.
Let's use it.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
--
Index: mmotm-0719/include/linux/page_cgroup.h
===================================================================
--- mmotm-0719.orig/include/linux/page_cgroup.h
+++ mmotm-0719/include/linux/page_cgroup.h
@@ -10,8 +10,14 @@
  * All page cgroups are allocated at boot or memory hotplug event,
  * then the page cgroup for pfn always exists.
  */
+#ifdef CONFIG_64BIT
+#define PCG_HAS_SPINLOCK
+#endif
 struct page_cgroup {
 	unsigned long flags;
+#ifdef PCG_HAS_SPINLOCK
+	spinlock_t	lock;
+#endif
 	unsigned short mem_cgroup;	/* ID of assigned memory cgroup */
 	unsigned short blk_cgroup;	/* Not Used..but will be. */
 	struct page *page;
@@ -90,6 +96,16 @@ static inline enum zone_type page_cgroup
 	return page_zonenum(pc->page);
 }
 
+#ifdef PCG_HAS_SPINLOCK
+static inline void lock_page_cgroup(struct page_cgroup *pc)
+{
+	spin_lock(&pc->lock);
+}
+static inline void unlock_page_cgroup(struct page_cgroup *pc)
+{
+	spin_unlock(&pc->lock);
+}
+#else
 static inline void lock_page_cgroup(struct page_cgroup *pc)
 {
 	bit_spin_lock(PCG_LOCK, &pc->flags);
@@ -99,6 +115,7 @@ static inline void unlock_page_cgroup(st
 {
 	bit_spin_unlock(PCG_LOCK, &pc->flags);
 }
+#endif
 
 static inline void SetPCGFileFlag(struct page_cgroup *pc, int idx)
 {
Index: mmotm-0719/mm/page_cgroup.c
===================================================================
--- mmotm-0719.orig/mm/page_cgroup.c
+++ mmotm-0719/mm/page_cgroup.c
@@ -17,6 +17,9 @@ __init_page_cgroup(struct page_cgroup *p
 	pc->mem_cgroup = 0;
 	pc->page = pfn_to_page(pfn);
 	INIT_LIST_HEAD(&pc->lru);
+#ifdef PCG_HAS_SPINLOCK
+	spin_lock_init(&pc->lock);
+#endif
 }
 static unsigned long total_usage;
 

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