quota: Make global quota locks cacheline aligned

Andrew Morton has suggested that three global quota locks can end up in the
same cacheline which can result in bad cacheline ping-pong on SMP machines.
Make locks cacheline aligned so that we avoid this problem (thanks goes to
Andrew for the idea).

Signed-off-by: Jan Kara <jack@suse.cz>
CC: Andrew Morton <akpm@linux-foundation.org>

diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c
index 28aa146..e840fa2 100644 (file)
--- a/fs/quota/dquot.c
+++ b/fs/quota/dquot.c
@@ -129,9 +129,9 @@
  * i_mutex on quota files is special (it's below dqio_mutex)
  */
 
-static DEFINE_SPINLOCK(dq_list_lock);
-static DEFINE_SPINLOCK(dq_state_lock);
-DEFINE_SPINLOCK(dq_data_lock);
+static __cacheline_aligned_in_smp DEFINE_SPINLOCK(dq_list_lock);
+static __cacheline_aligned_in_smp DEFINE_SPINLOCK(dq_state_lock);
+__cacheline_aligned_in_smp DEFINE_SPINLOCK(dq_data_lock);
 EXPORT_SYMBOL(dq_data_lock);
 
 static char *quotatypes[] = INITQFNAMES;