[patch] smarter atime updates

[Andrew Morton]

mark_inode_dirty() is quite expensive for journalling filesystems,
and we're calling it a lot more than we need to.

--- linux-2.4.17-pre1/fs/inode.c	Mon Nov 26 11:52:07 2001
+++ linux-akpm/fs/inode.c	Thu Nov 29 21:53:02 2001
@@ -1187,6 +1187,8 @@ void __init inode_init(unsigned long mem
  
 void update_atime (struct inode *inode)
 {
+	if (inode->i_atime == CURRENT_TIME)
+		return;
 	if ( IS_NOATIME (inode) ) return;
 	if ( IS_NODIRATIME (inode) && S_ISDIR (inode->i_mode) ) return;
 	if ( IS_RDONLY (inode) ) return;

with this patch, the time to read a 10 meg file with 10 million
read()s falls from 38 seconds (ext3), 39 seconds (reiserfs) and
11.6 seconds (ext2) down to 10.5 seconds.

-