[PATCH] Use __read_mostly on some hot fs variables

I discovered on oprofile hunting on a SMP platform that dentry lookups were
slowed down because d_hash_mask, d_hash_shift and dentry_hashtable were in
a cache line that contained inodes_stat.  So each time inodes_stats is
changed by a cpu, other cpus have to refill their cache line.

This patch moves some variables to the __read_mostly section, in order to
avoid false sharing.  RCU dentry lookups can go full speed.

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 4 insertions, 4 deletions

diff --git a/fs/inode.c b/fs/inode.c
index 85da11044adc..1fddf2803af8 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -56,8 +56,8 @@
 #define I_HASHBITS      i_hash_shift
 #define I_HASHMASK      i_hash_mask
 
-static unsigned int i_hash_mask;
-static unsigned int i_hash_shift;
+static unsigned int i_hash_mask __read_mostly;
+static unsigned int i_hash_shift __read_mostly;
 
 /*
  * Each inode can be on two separate lists. One is
@@ -73,7 +73,7 @@ static unsigned int i_hash_shift;
 
 LIST_HEAD(inode_in_use);
 LIST_HEAD(inode_unused);
-static struct hlist_head *inode_hashtable;
+static struct hlist_head *inode_hashtable __read_mostly;
 
 /*
  * A simple spinlock to protect the list manipulations.
@@ -98,7 +98,7 @@ static DEFINE_MUTEX(iprune_mutex);
  */
 struct inodes_stat_t inodes_stat;
 
-static kmem_cache_t * inode_cachep;
+static kmem_cache_t * inode_cachep __read_mostly;
 
 static struct inode *alloc_inode(struct super_block *sb)
 {