From: Nick Piggin <npiggin@suse.de>
Date: Sat, 26 Jul 2008 02:45:28 +0000 (-0700)
Subject: mm: readahead scan lockless
X-Git-Tag: v2.6.27-rc1~158
X-Git-Url: http://www.pilppa.org/gitweb/gitweb.cgi?a=commitdiff_plain;h=30002ed2e41830ec03ec3e577ad83ac6b188f96e;p=linux-2.6-omap-h63xx.git

mm: readahead scan lockless

radix_tree_next_hole() is implemented as a series of radix_tree_lookup()s.
So it can be called locklessly, under rcu_read_lock().

Signed-off-by: Nick Piggin <npiggin@suse.de>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Hugh Dickins <hugh@veritas.com>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Reviewed-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---

diff --git a/mm/readahead.c b/mm/readahead.c
index d8723a5f649..77e8ddf945e 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -382,9 +382,9 @@ ondemand_readahead(struct address_space *mapping,
 	if (hit_readahead_marker) {
 		pgoff_t start;
 
-		read_lock_irq(&mapping->tree_lock);
-		start = radix_tree_next_hole(&mapping->page_tree, offset, max+1);
-		read_unlock_irq(&mapping->tree_lock);
+		rcu_read_lock();
+		start = radix_tree_next_hole(&mapping->page_tree, offset,max+1);
+		rcu_read_unlock();
 
 		if (!start || start - offset > max)
 			return 0;