fs: Implement lazy LRU updates for inodes

Convert the inode LRU to use lazy updates to reduce lock and
cacheline traffic.  We avoid moving inodes around in the LRU list
during iget/iput operations so these frequent operations don't need
to access the LRUs. Instead, we defer the refcount checks to
reclaim-time and use a per-inode state flag, I_REFERENCED, to tell
reclaim that iget has touched the inode in the past. This means that
only reclaim should be touching the LRU with any frequency, hence
significantly reducing lock acquisitions and the amount contention
on LRU updates.

This also removes the inode_in_use list, which means we now only
have one list for tracking the inode LRU status. This makes it much
simpler to split out the LRU list operations under it's own lock.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

2 files changed, 7 insertions, 8 deletions

diff --git a/include/linux/fs.h b/include/linux/fs.h
index a3937a8ee95e..876275fc0638 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1641,16 +1641,17 @@ struct super_operations {
  *
  * Q: What is the difference between I_WILL_FREE and I_FREEING?
  */
-#define I_DIRTY_SYNC            1
-#define I_DIRTY_DATASYNC        2
-#define I_DIRTY_PAGES           4
+#define I_DIRTY_SYNC            (1 << 0)
+#define I_DIRTY_DATASYNC        (1 << 1)
+#define I_DIRTY_PAGES           (1 << 2)
 #define __I_NEW                 3
 #define I_NEW                   (1 << __I_NEW)
-#define I_WILL_FREE             16
-#define I_FREEING               32
-#define I_CLEAR                 64
+#define I_WILL_FREE             (1 << 4)
+#define I_FREEING               (1 << 5)
+#define I_CLEAR                 (1 << 6)
 #define __I_SYNC                7
 #define I_SYNC                  (1 << __I_SYNC)
+#define I_REFERENCED            (1 << 8)
 
 #define I_DIRTY (I_DIRTY_SYNC | I_DIRTY_DATASYNC | I_DIRTY_PAGES)
 
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 72a5d647a5f2..242b6f812ba6 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -10,8 +10,6 @@
 struct backing_dev_info;
 
 extern spinlock_t inode_lock;
-extern struct list_head inode_in_use;
-extern struct list_head inode_unused;
 
 /*
  * fs/fs-writeback.c