diff --git a/src/shrpx_client_handler.h b/src/shrpx_client_handler.h
index c441a5bd..bc4d7c27 100644
--- a/src/shrpx_client_handler.h
+++ b/src/shrpx_client_handler.h
@@ -165,6 +165,9 @@ public:
   BlockAllocator &get_block_allocator();
 
 private:
+  // Allocator to allocate memory for connection-wide objects.  Make
+  // sure that the allocations must be bounded, and not proportional
+  // to the number of requests.
   BlockAllocator balloc_;
   Connection conn_;
   ev_timer reneg_shutdown_timer_;
diff --git a/src/shrpx_config.h b/src/shrpx_config.h
index 6aa8cab6..527c13b6 100644
--- a/src/shrpx_config.h
+++ b/src/shrpx_config.h
@@ -659,7 +659,7 @@ struct RateLimitConfig {
 struct WildcardPattern {
   WildcardPattern(const StringRef &host) : host(host) {}
 
-  // This may not be NULL terminated.  Currently it is only used for
+  // This might not be NULL terminated.  Currently it is only used for
   // comparison.
   StringRef host;
   Router router;
@@ -693,6 +693,10 @@ struct DownstreamConfig {
   DownstreamConfig &operator=(const DownstreamConfig &) = delete;
   DownstreamConfig &operator=(DownstreamConfig &&) = delete;
 
+  // Allocator to allocate memory for Downstream configuration.  Since
+  // we may swap around DownstreamConfig in arbitrary times with API
+  // calls, we should use their own allocator instead of per Config
+  // allocator.
   BlockAllocator balloc;
   struct {
     ev_tstamp read;
@@ -781,6 +785,9 @@ struct Config {
   Config &operator=(Config &&) = delete;
   Config &operator=(const Config &&) = delete;
 
+  // Allocator to allocate memory for this object except for
+  // DownstreamConfig.  Currently, it is used to allocate memory for
+  // strings.
   BlockAllocator balloc;
   HttpProxy downstream_http_proxy;
   HttpConfig http;