[patch 6/6] mm: speculative refcount debug

[Nick Piggin <npiggin@suse.de>]

Add some debugging for lockless pagecache.

Signed-off-by: Nick Piggin <npiggin@suse.de>
---
Index: linux-2.6/include/linux/mm.h
===================================================================
--- linux-2.6.orig/include/linux/mm.h
+++ linux-2.6/include/linux/mm.h
@@ -236,9 +236,30 @@ static inline struct page *compound_head
 	return page;
 }
 
+#ifdef CONFIG_DEBUG_VM
+extern int ll_counter;
+#endif
+
 static inline int page_count(struct page *page)
 {
+#ifndef CONFIG_DEBUG_VM
 	return atomic_read(&compound_head(page)->_count);
+#else
+
+	int count;
+	/*
+	 * debug testing for lockless pagecache. add a random value to
+	 * page_count every now and then, to simulate speculative references
+	 * to it.
+	 */
+	count = atomic_read(&compound_head(page)->_count);
+	if (count) {
+		ll_counter++;
+		if (ll_counter % 5 == 0 || ll_counter % 7 == 0)
+			count += ll_counter % 11;
+	}
+	return count;
+#endif
 }
 
 static inline void get_page(struct page *page)
Index: linux-2.6/mm/page_alloc.c
===================================================================
--- linux-2.6.orig/mm/page_alloc.c
+++ linux-2.6/mm/page_alloc.c
@@ -173,6 +173,8 @@ static void set_pageblock_migratetype(st
 }
 
 #ifdef CONFIG_DEBUG_VM
+int ll_counter; /* used in include/linux/mm.h, for lockless pagecache */
+EXPORT_SYMBOL(ll_counter);
 static int page_outside_zone_boundaries(struct zone *zone, struct page *page)
 {
 	int ret = 0;

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