Now that radix_tree_tag_clear/set() are atomic we only need the rwlock for
reading in these places.

Signed-off-by: Andrew Morton <akpm@osdl.org>
---

 25-akpm/fs/buffer.c         |    4 ++--
 25-akpm/mm/page-writeback.c |   24 ++++++++++++------------
 2 files changed, 14 insertions(+), 14 deletions(-)

diff -puN mm/page-writeback.c~radix_tree_tag_set-only-needs-read_lock mm/page-writeback.c
--- 25/mm/page-writeback.c~radix_tree_tag_set-only-needs-read_lock	2004-06-14 00:11:19.649199784 -0700
+++ 25-akpm/mm/page-writeback.c	2004-06-14 00:11:19.656198720 -0700
@@ -582,7 +582,7 @@ int __set_page_dirty_nobuffers(struct pa
 		struct address_space *mapping = page_mapping(page);
 
 		if (mapping) {
-			write_lock_irq(&mapping->tree_lock);
+			read_lock_irq(&mapping->tree_lock);
 			mapping = page_mapping(page);
 			if (page_mapping(page)) { /* Race with truncate? */
 				BUG_ON(page_mapping(page) != mapping);
@@ -591,7 +591,7 @@ int __set_page_dirty_nobuffers(struct pa
 				radix_tree_tag_set(&mapping->page_tree,
 					page_index(page), PAGECACHE_TAG_DIRTY);
 			}
-			write_unlock_irq(&mapping->tree_lock);
+			read_unlock_irq(&mapping->tree_lock);
 			if (mapping->host) {
 				/* !PageAnon && !swapper_space */
 				__mark_inode_dirty(mapping->host,
@@ -666,17 +666,17 @@ int test_clear_page_dirty(struct page *p
 	unsigned long flags;
 
 	if (mapping) {
-		write_lock_irqsave(&mapping->tree_lock, flags);
+		read_lock_irqsave(&mapping->tree_lock, flags);
 		if (TestClearPageDirty(page)) {
 			radix_tree_tag_clear(&mapping->page_tree,
 						page_index(page),
 						PAGECACHE_TAG_DIRTY);
-			write_unlock_irqrestore(&mapping->tree_lock, flags);
+			read_unlock_irqrestore(&mapping->tree_lock, flags);
 			if (!mapping->backing_dev_info->memory_backed)
 				dec_page_state(nr_dirty);
 			return 1;
 		}
-		write_unlock_irqrestore(&mapping->tree_lock, flags);
+		read_unlock_irqrestore(&mapping->tree_lock, flags);
 		return 0;
 	}
 	return TestClearPageDirty(page);
@@ -723,15 +723,15 @@ int __clear_page_dirty(struct page *page
 	if (mapping) {
 		unsigned long flags;
 
-		write_lock_irqsave(&mapping->tree_lock, flags);
+		read_lock_irqsave(&mapping->tree_lock, flags);
 		if (TestClearPageDirty(page)) {
 			radix_tree_tag_clear(&mapping->page_tree,
 						page_index(page),
 						PAGECACHE_TAG_DIRTY);
-			write_unlock_irqrestore(&mapping->tree_lock, flags);
+			read_unlock_irqrestore(&mapping->tree_lock, flags);
 			return 1;
 		}
-		write_unlock_irqrestore(&mapping->tree_lock, flags);
+		read_unlock_irqrestore(&mapping->tree_lock, flags);
 		return 0;
 	}
 	return TestClearPageDirty(page);
@@ -745,13 +745,13 @@ int test_clear_page_writeback(struct pag
 	if (mapping) {
 		unsigned long flags;
 
-		write_lock_irqsave(&mapping->tree_lock, flags);
+		read_lock_irqsave(&mapping->tree_lock, flags);
 		ret = TestClearPageWriteback(page);
 		if (ret)
 			radix_tree_tag_clear(&mapping->page_tree,
 						page_index(page),
 						PAGECACHE_TAG_WRITEBACK);
-		write_unlock_irqrestore(&mapping->tree_lock, flags);
+		read_unlock_irqrestore(&mapping->tree_lock, flags);
 	} else {
 		ret = TestClearPageWriteback(page);
 	}
@@ -766,7 +766,7 @@ int test_set_page_writeback(struct page 
 	if (mapping) {
 		unsigned long flags;
 
-		write_lock_irqsave(&mapping->tree_lock, flags);
+		read_lock_irqsave(&mapping->tree_lock, flags);
 		ret = TestSetPageWriteback(page);
 		if (!ret)
 			radix_tree_tag_set(&mapping->page_tree,
@@ -776,7 +776,7 @@ int test_set_page_writeback(struct page 
 			radix_tree_tag_clear(&mapping->page_tree,
 						page_index(page),
 						PAGECACHE_TAG_DIRTY);
-		write_unlock_irqrestore(&mapping->tree_lock, flags);
+		read_unlock_irqrestore(&mapping->tree_lock, flags);
 	} else {
 		ret = TestSetPageWriteback(page);
 	}
diff -puN fs/buffer.c~radix_tree_tag_set-only-needs-read_lock fs/buffer.c
--- 25/fs/buffer.c~radix_tree_tag_set-only-needs-read_lock	2004-06-14 00:11:19.651199480 -0700
+++ 25-akpm/fs/buffer.c	2004-06-14 00:11:19.658198416 -0700
@@ -947,7 +947,7 @@ int __set_page_dirty_buffers(struct page
 	spin_unlock(&mapping->private_lock);
 
 	if (!TestSetPageDirty(page)) {
-		write_lock_irq(&mapping->tree_lock);
+		read_lock_irq(&mapping->tree_lock);
 		if (page->mapping) {	/* Race with truncate? */
 			if (!mapping->backing_dev_info->memory_backed)
 				inc_page_state(nr_dirty);
@@ -955,7 +955,7 @@ int __set_page_dirty_buffers(struct page
 						page_index(page),
 						PAGECACHE_TAG_DIRTY);
 		}
-		write_unlock_irq(&mapping->tree_lock);
+		read_unlock_irq(&mapping->tree_lock);
 		__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
 	}
 	
_