mm: use lockless radix-tree probe

Probing pages and radix_tree_tagged are lockless operations with the lockless
radix-tree.  Convert these users to RCU locking rather than using tree_lock.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 5 insertions, 9 deletions

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 44720363374c..2adb89959885 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -1022,17 +1022,15 @@ int test_set_page_writeback(struct page *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);
diff --git a/mm/readahead.c b/mm/readahead.c
index fc52f9f1b80c..c5c8981469e7 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -149,20 +149,19 @@ __do_page_cache_readahead(struct address_space *mapping, struct file *filp,
         /*
          * 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;
 
+                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;
@@ -171,7 +170,6 @@ __do_page_cache_readahead(struct address_space *mapping, struct file *filp,
                         SetPageReadahead(page);
                 ret++;
         }
-        read_unlock_irq(&mapping->tree_lock);
 
         /*
          * Now start the IO.  We ignore I/O errors - if the page is not