os/bluestore: default to 64k min_alloc_size

Signed-off-by: Sage Weil <sage@redhat.com>

src/common/config_opts.h

@@ -847,7 +847,7 @@ OPTION(bluestore_block_db_size, OPT_U64, 64 * 1024*1024)  // 64MB for testing
 OPTION(bluestore_block_wal_path, OPT_STR, "")
 OPTION(bluestore_block_wal_size, OPT_U64, 128 * 1024*1024)  // 128MB for testing
 OPTION(bluestore_max_dir_size, OPT_U32, 1000000)
-OPTION(bluestore_min_alloc_size, OPT_U32, 512*1024)
+OPTION(bluestore_min_alloc_size, OPT_U32, 64*1024)
 OPTION(bluestore_onode_map_size, OPT_U32, 1024)   // onodes per collection
 OPTION(bluestore_cache_tails, OPT_BOOL, true)   // cache tail blocks in Onode
 OPTION(bluestore_backend, OPT_STR, "rocksdb")