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>

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 6ce3c7c..65fe1dc 100644 (file)
--- 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;

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 9a3844a..4444317 100644 (file)
--- 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;
 }
-

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index fdce4ee..874dd25 100644 (file)
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2439,6 +2439,18 @@ static ssize_t lifetime_write_kbytes_show(struct ext4_attr *a,
                          EXT4_SB(sb)->s_sectors_written_start) >> 1)));
 }
 
+static ssize_t extent_cache_hits_show(struct ext4_attr *a,
+                                     struct ext4_sb_info *sbi, char *buf)
+{
+       return snprintf(buf, PAGE_SIZE, "%lu\n", sbi->extent_cache_hits);
+}
+
+static ssize_t extent_cache_misses_show(struct ext4_attr *a,
+                                       struct ext4_sb_info *sbi, char *buf)
+{
+       return snprintf(buf, PAGE_SIZE, "%lu\n", sbi->extent_cache_misses);
+}
+
 static ssize_t inode_readahead_blks_store(struct ext4_attr *a,
                                          struct ext4_sb_info *sbi,
                                          const char *buf, size_t count)
@@ -2496,6 +2508,8 @@ static struct ext4_attr ext4_attr_##name = __ATTR(name, mode, show, store)
 EXT4_RO_ATTR(delayed_allocation_blocks);
 EXT4_RO_ATTR(session_write_kbytes);
 EXT4_RO_ATTR(lifetime_write_kbytes);
+EXT4_RO_ATTR(extent_cache_hits);
+EXT4_RO_ATTR(extent_cache_misses);
 EXT4_ATTR_OFFSET(inode_readahead_blks, 0644, sbi_ui_show,
                 inode_readahead_blks_store, s_inode_readahead_blks);
 EXT4_RW_ATTR_SBI_UI(inode_goal, s_inode_goal);
@@ -2511,6 +2525,8 @@ static struct attribute *ext4_attrs[] = {
        ATTR_LIST(delayed_allocation_blocks),
        ATTR_LIST(session_write_kbytes),
        ATTR_LIST(lifetime_write_kbytes),
+       ATTR_LIST(extent_cache_hits),
+       ATTR_LIST(extent_cache_misses),
        ATTR_LIST(inode_readahead_blks),
        ATTR_LIST(inode_goal),
        ATTR_LIST(mb_stats),