lockless pagecache

Index: linux-2.6/lib/radix-tree.c
===================================================================
@@ -30,6 +30,7 @@
 #include <linux/gfp.h>
 #include <linux/string.h>
 #include <linux/bitops.h>
+#include <linux/rcupdate.h>
 
 
 #ifdef __KERNEL__

@@ -45,7 +46,9 @@
 	((RADIX_TREE_MAP_SIZE + BITS_PER_LONG - 1) / BITS_PER_LONG)
 
 struct radix_tree_node {
+	unsigned int	height;		/* Height from the bottom */
 	unsigned int	count;
+	struct rcu_head	rcu_head;
 	void		*slots[RADIX_TREE_MAP_SIZE];
 	unsigned long	tags[RADIX_TREE_MAX_TAGS][RADIX_TREE_TAG_LONGS];
 };

@@ -97,10 +100,17 @@ radix_tree_node_alloc(struct radix_tree_
 	return ret;
 }
 
+static void radix_tree_node_rcu_free(struct rcu_head *head)
+{
+	struct radix_tree_node *node =
+			container_of(head, struct radix_tree_node, rcu_head);
+	kmem_cache_free(radix_tree_node_cachep, node);
+}
+
 static inline void
 radix_tree_node_free(struct radix_tree_node *node)
 {
-	kmem_cache_free(radix_tree_node_cachep, node);
+	call_rcu(&node->rcu_head, radix_tree_node_rcu_free);
 }
 
 /*

@@ -206,6 +216,7 @@ static int radix_tree_extend(struct radi
 	}
 
 	do {
+		unsigned int newheight;
 		if (!(node = radix_tree_node_alloc(root)))
 			return -ENOMEM;
 

@@ -218,9 +229,11 @@ static int radix_tree_extend(struct radi
 				tag_set(node, tag, 0);
 		}
 
+		newheight = root->height+1;
+		node->height = newheight;
 		node->count = 1;
-		root->rnode = node;
-		root->height++;
+		rcu_assign_pointer(root->rnode, node);
+		root->height = newheight;
 	} while (height > root->height);
 out:
 	return 0;

@@ -260,11 +273,12 @@ int radix_tree_insert(struct radix_tree_
 			/* Have to add a child node.  */
 			if (!(slot = radix_tree_node_alloc(root)))
 				return -ENOMEM;
+			slot->height = height;
 			if (node) {
-				node->slots[offset] = slot;
+				rcu_assign_pointer(node->slots[offset], slot);
 				node->count++;
 			} else
-				root->rnode = slot;
+				rcu_assign_pointer(root->rnode, slot);
 		}
 
 		/* Go a level down */

@@ -280,7 +294,7 @@ int radix_tree_insert(struct radix_tree_
 
 	BUG_ON(!node);
 	node->count++;
-	node->slots[offset] = item;
+	rcu_assign_pointer(node->slots[offset], item);
 	BUG_ON(tag_get(node, 0, offset));
 	BUG_ON(tag_get(node, 1, offset));
 

@@ -292,25 +306,29 @@ static inline void **__lookup_slot(struc
 				   unsigned long index)
 {
 	unsigned int height, shift;
-	struct radix_tree_node **slot;
+	struct radix_tree_node *node, **slot;
 
-	height = root->height;
+	/* Must take a copy now because root->rnode may change */
+	node = rcu_dereference(root->rnode);
+	if (node == NULL)
+		return NULL;
+
+	height = node->height;
 	if (index > radix_tree_maxindex(height))
 		return NULL;
 
 	shift = (height-1) * RADIX_TREE_MAP_SHIFT;
-	slot = &root->rnode;
 
-	while (height > 0) {
-		if (*slot == NULL)
+	do {
+		slot = (struct radix_tree_node **)
+			(node->slots + ((index>>shift) & RADIX_TREE_MAP_MASK));
+		node = rcu_dereference(*slot);
+		if (node == NULL)
 			return NULL;
 
-		slot = (struct radix_tree_node **)
-			((*slot)->slots +
-				((index >> shift) & RADIX_TREE_MAP_MASK));
 		shift -= RADIX_TREE_MAP_SHIFT;
 		height--;
-	}
+	} while (height > 0);
 
 	return (void **)slot;
 }

@@ -322,6 +340,12 @@ static inline void **__lookup_slot(struc
  *
  *	Lookup the slot corresponding to the position @index in the radix tree
  *	@root. This is useful for update-if-exists operations.
+ *
+ *	This function can be called under rcu_read_lock, however it is the
+ *	duty of the caller to manage the lifetimes of the leaf nodes (ie.
+ *	they would usually be RCU protected as well). Also, dereferencing
+ *	the slot pointer would require rcu_dereference, and modifying it
+ *	would require rcu_assign_pointer.
  */
 void **radix_tree_lookup_slot(struct radix_tree_root *root, unsigned long index)
 {

@@ -335,13 +359,18 @@ EXPORT_SYMBOL(radix_tree_lookup_slot);
  *	@index:		index key
  *
  *	Lookup the item at the position @index in the radix tree @root.
+ *
+ *	Like radix_tree_lookup_slot, this function can be called under
+ *	rcu_read_lock, and likewise the caller must manage lifetimes of
+ *	leaf nodes. No RCU barriers are required to access or modify the
+ *	returned item, however.
  */
 void *radix_tree_lookup(struct radix_tree_root *root, unsigned long index)
 {
 	void **slot;
 
 	slot = __lookup_slot(root, index);
-	return slot != NULL ? *slot : NULL;
+	return slot != NULL ? rcu_dereference(*slot) : NULL;
 }
 EXPORT_SYMBOL(radix_tree_lookup);
 

@@ -505,7 +534,7 @@ EXPORT_SYMBOL(radix_tree_tag_get);
 #endif
 
 static unsigned int
-__lookup(struct radix_tree_root *root, void **results, unsigned long index,
+__lookup(struct radix_tree_root *root, void ***results, unsigned long index,
 	unsigned int max_items, unsigned long *next_index)
 {
 	unsigned int nr_found = 0;

@@ -513,18 +542,20 @@ __lookup(struct radix_tree_root *root, v
 	struct radix_tree_node *slot;
 	unsigned long i;
 
-	height = root->height;
-	if (height == 0)
+	slot = rcu_dereference(root->rnode);
+	if (!slot || slot->height == 0)
 		goto out;
 
+	height = slot->height;
 	shift = (height-1) * RADIX_TREE_MAP_SHIFT;
-	slot = root->rnode;
 
 	for ( ; height > 1; height--) {
+		struct radix_tree_node *__s;
 
 		for (i = (index >> shift) & RADIX_TREE_MAP_MASK ;
 				i < RADIX_TREE_MAP_SIZE; i++) {
-			if (slot->slots[i] != NULL)
+			__s = rcu_dereference(slot->slots[i]);
+			if (__s != NULL)
 				break;
 			index &= ~((1UL << shift) - 1);
 			index += 1UL << shift;

@@ -535,14 +566,14 @@ __lookup(struct radix_tree_root *root, v
 			goto out;
 
 		shift -= RADIX_TREE_MAP_SHIFT;
-		slot = slot->slots[i];
+		slot = __s;
 	}
 
 	/* Bottom level: grab some items */
 	for (i = index & RADIX_TREE_MAP_MASK; i < RADIX_TREE_MAP_SIZE; i++) {
 		index++;
 		if (slot->slots[i]) {
-			results[nr_found++] = slot->slots[i];
+			results[nr_found++] = &slot->slots[i];
 			if (nr_found == max_items)
 				goto out;
 		}

@@ -572,6 +603,46 @@ radix_tree_gang_lookup(struct radix_tree
 	const unsigned long max_index = radix_tree_maxindex(root->height);
 	unsigned long cur_index = first_index;
 	unsigned int ret = 0;
+	void ***__results = (void ***)results; /* use results as a temporary
+						* store for the pointers to
+						* the actual results */
+
+	while (ret < max_items) {
+		unsigned int nr_found, i;
+		unsigned long next_index;	/* Index of next search */
+
+		if (cur_index > max_index)
+			break;
+		nr_found = __lookup(root, __results + ret, cur_index,
+					max_items - ret, &next_index);
+		for (i = 0; i < nr_found; i++)
+			results[ret + i] = *rcu_dereference(__results[ret + i]);
+		ret += nr_found;
+		if (next_index == 0)
+			break;
+		cur_index = next_index;
+	}
+	return ret;
+}
+EXPORT_SYMBOL(radix_tree_gang_lookup);
+
+/**
+ *	radix_tree_gang_lookup_slot - perform multiple lookup on a radix tree
+ *	@root:		radix tree root
+ *	@results:	where the results of the lookup are placed
+ *	@first_index:	start the lookup from this key
+ *	@max_items:	place up to this many items at *results
+ *
+ *	Same as radix_tree_gang_lookup, but returns an array of pointers
+ *	(slots) to the stored items instead of the items themselves.
+ */
+unsigned int
+radix_tree_gang_lookup_slot(struct radix_tree_root *root, void ***results,
+			unsigned long first_index, unsigned int max_items)
+{
+	const unsigned long max_index = radix_tree_maxindex(root->height);
+	unsigned long cur_index = first_index;
+	unsigned int ret = 0;
 
 	while (ret < max_items) {
 		unsigned int nr_found;

@@ -588,7 +659,8 @@ radix_tree_gang_lookup(struct radix_tree
 	}
 	return ret;
 }
-EXPORT_SYMBOL(radix_tree_gang_lookup);
+EXPORT_SYMBOL_GPL(radix_tree_gang_lookup_slot);
+
 
 /*
  * FIXME: the two tag_get()s here should use find_next_bit() instead of

@@ -694,6 +766,11 @@ static inline void radix_tree_shrink(str
 			root->rnode->slots[0]) {
 		struct radix_tree_node *to_free = root->rnode;
 
+		/*
+		 * this doesn't need an rcu_assign_pointer, because
+		 * we aren't touching the object that to_free->slots[0]
+		 * points to.
+		 */
 		root->rnode = to_free->slots[0];
 		root->height--;
 		/* must only free zeroed nodes into the slab */

@@ -809,7 +886,7 @@ EXPORT_SYMBOL(radix_tree_delete);
 int radix_tree_tagged(struct radix_tree_root *root, unsigned int tag)
 {
   	struct radix_tree_node *rnode;
-  	rnode = root->rnode;
+  	rnode = rcu_dereference(root->rnode);
   	if (!rnode)
   		return 0;
 	return any_tag_set(rnode, tag);

Index: linux-2.6/include/linux/radix-tree.h
===================================================================
@@ -54,6 +54,9 @@ void *radix_tree_delete(struct radix_tre
 unsigned int
 radix_tree_gang_lookup(struct radix_tree_root *root, void **results,
 			unsigned long first_index, unsigned int max_items);
+unsigned int
+radix_tree_gang_lookup_slot(struct radix_tree_root *root, void ***results,
+			unsigned long first_index, unsigned int max_items);
 int radix_tree_preload(gfp_t gfp_mask);
 void radix_tree_init(void);
 void *radix_tree_tag_set(struct radix_tree_root *root,

Index: linux-2.6/include/linux/page-flags.h
===================================================================
@@ -76,6 +76,9 @@
 #define PG_nosave_free		18	/* Free, should not be written */
 #define PG_uncached		19	/* Page has been mapped as uncached */
 
+#define PG_nonewrefs		20	/* Block concurrent pagecache lookups
+					 * while testing refcount */
+
 /*
  * Global page accounting.  One instance per CPU.  Only unsigned longs are
  * allowed.

@@ -346,6 +349,11 @@ extern void __mod_page_state_offset(unsi
 #define SetPageUncached(page)	set_bit(PG_uncached, &(page)->flags)
 #define ClearPageUncached(page)	clear_bit(PG_uncached, &(page)->flags)
 
+#define PageNoNewRefs(page)	test_bit(PG_nonewrefs, &(page)->flags)
+#define SetPageNoNewRefs(page)	set_bit(PG_nonewrefs, &(page)->flags)
+#define ClearPageNoNewRefs(page) clear_bit(PG_nonewrefs, &(page)->flags)
+#define __ClearPageNoNewRefs(page) __clear_bit(PG_nonewrefs, &(page)->flags)
+
 struct page;	/* forward declaration */
 
 int test_clear_page_dirty(struct page *page);

99 lines not on this page · raw message

Index: linux-2.6/mm/vmscan.c
===================================================================
@@ -365,6 +365,7 @@ int remove_mapping(struct address_space 
 	if (!mapping)
 		return 0;		/* truncate got there first */
 
+	SetPageNoNewRefs(page);
 	write_lock_irq(&mapping->tree_lock);
 
 	/*

@@ -383,17 +384,20 @@ int remove_mapping(struct address_space 
 		__delete_from_swap_cache(page);
 		write_unlock_irq(&mapping->tree_lock);
 		swap_free(swap);
-		__put_page(page);	/* The pagecache ref */
-		return 1;
+		goto free_it;
 	}
 
 	__remove_from_page_cache(page);
 	write_unlock_irq(&mapping->tree_lock);
-	__put_page(page);
+
+free_it:
+	__ClearPageNoNewRefs(page);
+	__put_page(page); /* The pagecache ref */
 	return 1;
 
 cannot_free:
 	write_unlock_irq(&mapping->tree_lock);
+	ClearPageNoNewRefs(page);
 	return 0;
 }
 

Index: linux-2.6/mm/filemap.c
===================================================================
@@ -407,6 +407,7 @@ int add_to_page_cache(struct page *page,
 	int error = radix_tree_preload(gfp_mask & ~__GFP_HIGHMEM);
 
 	if (error == 0) {
+		SetPageNoNewRefs(page);
 		write_lock_irq(&mapping->tree_lock);
 		error = radix_tree_insert(&mapping->page_tree, offset, page);
 		if (!error) {

@@ -418,6 +419,7 @@ int add_to_page_cache(struct page *page,
 			pagecache_acct(1);
 		}
 		write_unlock_irq(&mapping->tree_lock);
+		ClearPageNoNewRefs(page);
 		radix_tree_preload_end();
 	}
 	return error;

Index: linux-2.6/mm/swap_state.c
===================================================================
@@ -78,6 +78,7 @@ static int __add_to_swap_cache(struct pa
 	BUG_ON(PagePrivate(page));
 	error = radix_tree_preload(gfp_mask);
 	if (!error) {
+		SetPageNoNewRefs(page);
 		write_lock_irq(&swapper_space.tree_lock);
 		error = radix_tree_insert(&swapper_space.page_tree,
 						entry.val, page);

@@ -90,6 +91,7 @@ static int __add_to_swap_cache(struct pa
 			pagecache_acct(1);
 		}
 		write_unlock_irq(&swapper_space.tree_lock);
+		ClearPageNoNewRefs(page);
 		radix_tree_preload_end();
 	}
 	return error;

Index: linux-2.6/mm/migrate.c
===================================================================
@@ -28,8 +28,6 @@
 
 #include "internal.h"
 
-#include "internal.h"
-
 /* The maximum number of pages to take off the LRU for migration */
 #define MIGRATE_CHUNK_SIZE 256
 

@@ -225,6 +223,7 @@ int migrate_page_remove_references(struc
 	if (page_mapcount(page))
 		return -EAGAIN;
 
+	SetPageNoNewRefs(page);
 	write_lock_irq(&mapping->tree_lock);
 
 	radix_pointer = (struct page **)radix_tree_lookup_slot(

@@ -234,6 +233,7 @@ int migrate_page_remove_references(struc
 	if (!page_mapping(page) || page_count(page) != nr_refs ||
 			*radix_pointer != page) {
 		write_unlock_irq(&mapping->tree_lock);
+		ClearPageNoNewRefs(page);
 		return 1;
 	}
 

@@ -253,9 +253,13 @@ int migrate_page_remove_references(struc
 		set_page_private(newpage, page_private(page));
 	}
 
-	*radix_pointer = newpage;
+	SetPageNoNewRefs(newpage);
+	rcu_assign_pointer(*radix_pointer, newpage);
+
+  	write_unlock_irq(&mapping->tree_lock);
 	__put_page(page);
-	write_unlock_irq(&mapping->tree_lock);
+	ClearPageNoNewRefs(page);
+	ClearPageNoNewRefs(newpage);
 
 	return 0;
 }

Index: linux-2.6/mm/filemap.c
===================================================================
@@ -424,7 +424,6 @@ int add_to_page_cache(struct page *page,
 	}
 	return error;
 }
-
 EXPORT_SYMBOL(add_to_page_cache);
 
 int add_to_page_cache_lru(struct page *page, struct address_space *mapping,

@@ -547,21 +546,21 @@ void fastcall __lock_page(struct page *p
 EXPORT_SYMBOL(__lock_page);
 
 /*
- * a rather lightweight function, finding and getting a reference to a
- * hashed page atomically.
+ * find_get_page finds and gets a reference to a pagecache page.
  */
-struct page * find_get_page(struct address_space *mapping, unsigned long offset)
+struct page *find_get_page(struct address_space *mapping, unsigned long offset)
 {
-	struct page *page;
+	struct page **pagep;
+	struct page *page = NULL;
 
-	read_lock_irq(&mapping->tree_lock);
-	page = radix_tree_lookup(&mapping->page_tree, offset);
-	if (page)
-		page_cache_get(page);
-	read_unlock_irq(&mapping->tree_lock);
+	rcu_read_lock();
+	pagep = (struct page **)radix_tree_lookup_slot(&mapping->page_tree,
+									offset);
+	if (likely(pagep))
+		page = page_cache_get_speculative(pagep);
+	rcu_read_unlock();
 	return page;
 }
-
 EXPORT_SYMBOL(find_get_page);
 
 /*

@@ -597,26 +596,17 @@ struct page *find_lock_page(struct addre
 {
 	struct page *page;
 
-	read_lock_irq(&mapping->tree_lock);
 repeat:
-	page = radix_tree_lookup(&mapping->page_tree, offset);
+	page = find_get_page(mapping, offset);
 	if (page) {
-		page_cache_get(page);
-		if (TestSetPageLocked(page)) {
-			read_unlock_irq(&mapping->tree_lock);
-			__lock_page(page);
-			read_lock_irq(&mapping->tree_lock);
-
-			/* Has the page been truncated while we slept? */
-			if (unlikely(page->mapping != mapping ||
-				     page->index != offset)) {
-				unlock_page(page);
-				page_cache_release(page);
-				goto repeat;
-			}
+		lock_page(page);
+		/* Has the page been truncated while we slept? */
+		if (unlikely(page->mapping != mapping)) {
+			unlock_page(page);
+			page_cache_release(page);
+			goto repeat;
 		}
 	}
-	read_unlock_irq(&mapping->tree_lock);
 	return page;
 }
 

@@ -699,6 +689,32 @@ unsigned find_get_pages(struct address_s
 	return ret;
 }
 
+unsigned find_get_pages_nonatomic(struct address_space *mapping, pgoff_t start,
+			    unsigned int nr_pages, struct page **pages)
+{
+	unsigned int i;
+	unsigned int nr_found;
+	unsigned int ret;
+
+	/*
+	 * We do some unsightly casting to use the array first for storing
+	 * pointers to the page pointers, and then for the pointers to
+	 * the pages themselves that the caller wants.
+	 */
+	rcu_read_lock();
+	nr_found = radix_tree_gang_lookup_slot(&mapping->page_tree,
+				(void ***)pages, start, nr_pages);
+	ret = 0;
+	for (i = 0; i < nr_found; i++) {
+		struct page *page;
+		page = page_cache_get_speculative(((struct page ***)pages)[i]);
+		if (likely(page))
+			pages[ret++] = page;
+	}
+	rcu_read_unlock();
+	return ret;
+}
+
 /*
  * Like find_get_pages, except we only return pages which are tagged with
  * `tag'.   We update *index to index the next page for the traversal.

Index: linux-2.6/mm/readahead.c
===================================================================
@@ -286,27 +286,26 @@ __do_page_cache_readahead(struct address
 	/*
 	 * Preallocate as many pages as we will need.
 	 */
-	read_lock_irq(&mapping->tree_lock);
 	for (page_idx = 0; page_idx < nr_to_read; page_idx++) {
 		pgoff_t page_offset = offset + page_idx;
 		
 		if (page_offset > end_index)
 			break;
 
+		/* Don't need mapping->tree_lock - lookup can be racy */
+		rcu_read_lock();
 		page = radix_tree_lookup(&mapping->page_tree, page_offset);
+		rcu_read_unlock();
 		if (page)
 			continue;
 
-		read_unlock_irq(&mapping->tree_lock);
 		page = page_cache_alloc_cold(mapping);
-		read_lock_irq(&mapping->tree_lock);
 		if (!page)
 			break;
 		page->index = page_offset;
 		list_add(&page->lru, &page_pool);
 		ret++;
 	}
-	read_unlock_irq(&mapping->tree_lock);
 
 	/*
 	 * Now start the IO.  We ignore I/O errors - if the page is not

Index: linux-2.6/include/linux/pagemap.h
===================================================================
@@ -165,6 +165,8 @@ extern struct page * find_or_create_page
 				unsigned long index, gfp_t gfp_mask);
 unsigned find_get_pages(struct address_space *mapping, pgoff_t start,
 			unsigned int nr_pages, struct page **pages);
+unsigned find_get_pages_nonatomic(struct address_space *mapping, pgoff_t start,
+			unsigned int nr_pages, struct page **pages);
 unsigned find_get_pages_tag(struct address_space *mapping, pgoff_t *index,
 			int tag, unsigned int nr_pages, struct page **pages);
 

Index: linux-2.6/include/linux/pagevec.h
===================================================================
@@ -28,6 +28,8 @@ void __pagevec_lru_add_active(struct pag
 void pagevec_strip(struct pagevec *pvec);
 unsigned pagevec_lookup(struct pagevec *pvec, struct address_space *mapping,
 		pgoff_t start, unsigned nr_pages);
+unsigned pagevec_lookup_nonatomic(struct pagevec *pvec,
+	struct address_space *mapping, pgoff_t start, unsigned nr_pages);
 unsigned pagevec_lookup_tag(struct pagevec *pvec,
 		struct address_space *mapping, pgoff_t *index, int tag,
 		unsigned nr_pages);

Index: linux-2.6/mm/swap.c
===================================================================
@@ -427,6 +427,20 @@ unsigned pagevec_lookup(struct pagevec *
 
 EXPORT_SYMBOL(pagevec_lookup);
 
+/**
+ * pagevec_lookup_nonatomic - non atomic pagevec_lookup
+ *
+ * This routine is non-atomic in that it may return blah.
+ */
+unsigned pagevec_lookup_nonatomic(struct pagevec *pvec,
+		struct address_space *mapping, pgoff_t start, unsigned nr_pages)
+{
+	pvec->nr = find_get_pages_nonatomic(mapping, start,
+					nr_pages, pvec->pages);
+	return pagevec_count(pvec);
+}
+EXPORT_SYMBOL(pagevec_lookup_nonatomic);
+
 unsigned pagevec_lookup_tag(struct pagevec *pvec, struct address_space *mapping,
 		pgoff_t *index, int tag, unsigned nr_pages)
 {

Index: linux-2.6/mm/truncate.c
===================================================================
@@ -124,7 +124,7 @@ void truncate_inode_pages_range(struct a
 	pagevec_init(&pvec, 0);
 	next = start;
 	while (next <= end &&
-	       pagevec_lookup(&pvec, mapping, next, PAGEVEC_SIZE)) {
+	       pagevec_lookup_nonatomic(&pvec, mapping, next, PAGEVEC_SIZE)) {
 		for (i = 0; i < pagevec_count(&pvec); i++) {
 			struct page *page = pvec.pages[i];
 			pgoff_t page_index = page->index;

@@ -163,7 +163,7 @@ void truncate_inode_pages_range(struct a
 	next = start;
 	for ( ; ; ) {
 		cond_resched();
-		if (!pagevec_lookup(&pvec, mapping, next, PAGEVEC_SIZE)) {
+		if (!pagevec_lookup_nonatomic(&pvec, mapping, next, PAGEVEC_SIZE)) {
 			if (next == start)
 				break;
 			next = start;

@@ -227,7 +227,7 @@ unsigned long invalidate_mapping_pages(s
 
 	pagevec_init(&pvec, 0);
 	while (next <= end &&
-			pagevec_lookup(&pvec, mapping, next, PAGEVEC_SIZE)) {
+		pagevec_lookup_nonatomic(&pvec, mapping, next, PAGEVEC_SIZE)) {
 		for (i = 0; i < pagevec_count(&pvec); i++) {
 			struct page *page = pvec.pages[i];
 

@@ -284,7 +284,7 @@ int invalidate_inode_pages2_range(struct
 	pagevec_init(&pvec, 0);
 	next = start;
 	while (next <= end && !ret && !wrapped &&
-		pagevec_lookup(&pvec, mapping, next,
+		pagevec_lookup_nonatomic(&pvec, mapping, next,
 			min(end - next, (pgoff_t)PAGEVEC_SIZE - 1) + 1)) {
 		for (i = 0; !ret && i < pagevec_count(&pvec); i++) {
 			struct page *page = pvec.pages[i];

Index: linux-2.6/mm/page-writeback.c
===================================================================
@@ -816,17 +816,15 @@ int test_set_page_writeback(struct page 
 EXPORT_SYMBOL(test_set_page_writeback);
 
 /*
- * Return true if any of the pages in the mapping are marged with the
+ * Return true if any of the pages in the mapping are marked with the
  * passed tag.
  */
 int mapping_tagged(struct address_space *mapping, int tag)
 {
-	unsigned long flags;
 	int ret;
-
-	read_lock_irqsave(&mapping->tree_lock, flags);
+	rcu_read_lock();
 	ret = radix_tree_tagged(&mapping->page_tree, tag);
-	read_unlock_irqrestore(&mapping->tree_lock, flags);
+	rcu_read_unlock();
 	return ret;
 }
 EXPORT_SYMBOL(mapping_tagged);