ext4: count hits/misses of extent cache and expose in sysfs

The number of hits and misses for each filesystem is exposed in
/sys/fs/ext4/<dev>/extent_cache_{hits, misses}.

Tested: fsstress, manual checks.
Signed-off-by: Vivek Haldar <haldar@google.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 3 insertions, 0 deletions

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 6ce3c7c8574c..65fe1dc0c750 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1144,6 +1144,9 @@ struct ext4_sb_info {
         unsigned long s_ext_blocks;
         unsigned long s_ext_extents;
 #endif
+        /* ext4 extent cache stats */
+        unsigned long extent_cache_hits;
+        unsigned long extent_cache_misses;
 
         /* for buddy allocator */
         struct ext4_group_info ***s_group_info;