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, 6 insertions, 1 deletions

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 9a3844adb1cb..4444317d141a 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -2035,6 +2035,7 @@ ext4_ext_in_cache(struct inode *inode, ext4_lblk_t block,
                         struct ext4_extent *ex)
 {
         struct ext4_ext_cache *cex;
+        struct ext4_sb_info *sbi;
         int ret = 0;
 
         /*
@@ -2042,6 +2043,7 @@ ext4_ext_in_cache(struct inode *inode, ext4_lblk_t block,
          */
         spin_lock(&EXT4_I(inode)->i_block_reservation_lock);
         cex = &EXT4_I(inode)->i_cached_extent;
+        sbi = EXT4_SB(inode->i_sb);
 
         /* has cache valid data? */
         if (cex->ec_len == 0)
@@ -2057,6 +2059,10 @@ ext4_ext_in_cache(struct inode *inode, ext4_lblk_t block,
                 ret = 1;
         }
 errout:
+        if (!ret)
+                sbi->extent_cache_misses++;
+        else
+                sbi->extent_cache_hits++;
         spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);
         return ret;
 }
@@ -3901,4 +3907,3 @@ int ext4_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
 
         return error;
 }
-