add buffer_count_max to SourceConfig

Mirror upstream dogstatsd_buffer_count_max (elastic
pool ceiling, default 256) into the Saluki-only
config path.

Author: webern

lib/agent-data-plane-config/src/saluki_only.rs

@@ -41,6 +41,9 @@ pub struct DogStatsDSalukiOnly {
     /// Number of receive buffers (`dogstatsd_buffer_count`).
     pub buffer_count: Option<usize>,
 
+    /// Max receive buffers (`dogstatsd_buffer_count_max`).
+    pub buffer_count_max: Option<usize>,
+
     /// Max cached metric contexts (`dogstatsd_cached_contexts_limit`).
     pub cached_contexts_limit: Option<usize>,
 
@@ -79,6 +82,9 @@ impl SalukiOnlyConfiguration {
         if let Some(v) = self.dogstatsd.buffer_count {
             dsd.buffer_count = v;
         }
+        if let Some(v) = self.dogstatsd.buffer_count_max {
+            dsd.buffer_count_max = v;
+        }
         if let Some(v) = self.dogstatsd.cached_contexts_limit {
             dsd.cached_contexts_limit = v;
         }

lib/saluki-component-config/src/dogstatsd.rs

@@ -26,11 +26,17 @@ pub struct SourceConfig {
     /// Payloads larger than this are truncated, leading to discarded messages. Defaults to 8192.
     pub buffer_size: usize,
 
-    /// The number of message buffers to allocate overall.
+    /// The number of message buffers to allocate up front.
     ///
     /// Defaults to 128.
     pub buffer_count: usize,
 
+    /// The maximum number of message buffers to allocate overall.
+    ///
+    /// The pool grows on demand from `buffer_count` up to this limit. A value below `buffer_count`
+    /// is treated as equal to it. Defaults to 256.
+    pub buffer_count_max: usize,
+
     /// The UDP port to listen on. If set to `0`, UDP is not used.
     ///
     /// Defaults to 8125.
@@ -170,6 +176,7 @@ impl Default for SourceConfig {
         Self {
             buffer_size: 8192,
             buffer_count: 128,
+            buffer_count_max: 256,
             port: 8125,
             socket_receive_buffer_size: 0,
             tcp_port: 0,