ext4: correct the cache_nr in tracepoint ext4_es_shrink_exit

The cache_cnt parameter of tracepoint ext4_es_shrink_exit means the
remaining cache count after shrink, but now it is the cache count before
shrink, fix it by read sbi->s_extent_cache_cnt again.

Fixes: 1ab6c49 ("fs: convert fs shrinkers to new scan/count API")
Cc: [email protected] # 3.12+
Signed-off-by: Zhang Yi <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Theodore Ts'o <[email protected]>

fs/ext4/extents_status.c

@@ -1576,6 +1576,7 @@ static unsigned long ext4_es_scan(struct shrinker *shrink,
 
 	nr_shrunk = __es_shrink(sbi, nr_to_scan, NULL);
 
+	ret = percpu_counter_read_positive(&sbi->s_es_stats.es_stats_shk_cnt);
 	trace_ext4_es_shrink_scan_exit(sbi->s_sb, nr_shrunk, ret);
 	return nr_shrunk;
 }