commit 19fd6231279be3c3bdd02ed99f9b0eb195978064
author Nick Piggin <npiggin@suse.de> Fri Jul 25 19:45:32 2008 -0700
committer Linus Torvalds <torvalds@linux-foundation.org> Sat Jul 26 12:00:06 2008 -0700
tree ee09121054262d73c551b57114acd855b82a7a82
parent a60637c85893e7191faaafa6a72e197c24386727

mm: spinlock tree_lock

mapping->tree_lock has no read lockers.  convert the lock from an rwlock
to a spinlock.

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>

mm/migrate.c

diff --git a/mm/migrate.c b/mm/migrate.c
index 3ca6392..153572f 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -323,7 +323,7 @@
 		return 0;
 	}
 
-	write_lock_irq(&mapping->tree_lock);
+	spin_lock_irq(&mapping->tree_lock);
 
 	pslot = radix_tree_lookup_slot(&mapping->page_tree,
  					page_index(page));
@@ -331,12 +331,12 @@
 	expected_count = 2 + !!PagePrivate(page);
 	if (page_count(page) != expected_count ||
 			(struct page *)radix_tree_deref_slot(pslot) != page) {
-		write_unlock_irq(&mapping->tree_lock);
+		spin_unlock_irq(&mapping->tree_lock);
 		return -EAGAIN;
 	}
 
 	if (!page_freeze_refs(page, expected_count)) {
-		write_unlock_irq(&mapping->tree_lock);
+		spin_unlock_irq(&mapping->tree_lock);
 		return -EAGAIN;
 	}
 
@@ -373,10 +373,9 @@
 	__dec_zone_page_state(page, NR_FILE_PAGES);
 	__inc_zone_page_state(newpage, NR_FILE_PAGES);
 
-	write_unlock_irq(&mapping->tree_lock);
-	if (!PageSwapCache(newpage)) {
+	spin_unlock_irq(&mapping->tree_lock);
+	if (!PageSwapCache(newpage))
 		mem_cgroup_uncharge_cache_page(page);
-	}
 
 	return 0;
 }