[Chttp2Transport] Flush data out over the transport quickly under high memory pressure. The change is protected under an experiment: disable_buffer_hint_on_high_memory_pressure

PiperOrigin-RevId: 694625426

bazel/experiments.bzl

@@ -21,6 +21,7 @@ EXPERIMENT_ENABLES = {
     "canary_client_privacy": "canary_client_privacy",
     "chaotic_good_legacy_protocol": "chaotic_good_legacy_protocol",
     "client_privacy": "client_privacy",
+    "disable_buffer_hint_on_high_memory_pressure": "disable_buffer_hint_on_high_memory_pressure",
     "event_engine_application_callbacks": "event_engine_application_callbacks",
     "event_engine_callback_cq": "event_engine_application_callbacks,event_engine_callback_cq",
     "event_engine_client": "event_engine_client",

src/core/ext/transport/chttp2/transport/chttp2_transport.cc

@@ -32,6 +32,7 @@
 #include <algorithm>
 #include <atomic>
 #include <cstddef>
+#include <cstdint>
 #include <limits>
 #include <memory>
 #include <new>
@@ -1470,7 +1471,7 @@ static void send_message_locked(
       op->payload->send_message.send_message->Length());
   on_complete->next_data.scratch |= t->closure_barrier_may_cover_write;
   s->send_message_finished = add_closure_barrier(op->on_complete);
-  const uint32_t flags = op_payload->send_message.flags;
+  uint32_t flags = 0;
   if (s->write_closed) {
     op->payload->send_message.stream_write_closed = true;
     // We should NOT return an error here, so as to avoid a cancel OP being
@@ -1480,6 +1481,19 @@ static void send_message_locked(
                                       absl::OkStatus(),
                                       "fetching_send_message_finished");
   } else {
+    // Buffer hint is used to buffer the message in the transport until the
+    // write buffer size (specified through GRPC_ARG_HTTP2_WRITE_BUFFER_SIZE) is
+    // reached. This is to batch writes sent down to tcp. However, if the memory
+    // pressure is high, disable the buffer hint to flush data down to tcp as
+    // soon as possible to avoid OOM.
+    if (grpc_core::IsDisableBufferHintOnHighMemoryPressureEnabled() &&
+        t->memory_owner.GetPressureInfo().pressure_control_value >= 0.8) {
+      // Disable write buffer hint if memory pressure is high. The value of 0.8
+      // is chosen to match the threshold used by the tcp endpoint (in
+      // allocating memory for socket reads).
+      op_payload->send_message.flags &= ~GRPC_WRITE_BUFFER_HINT;
+    }
+    flags = op_payload->send_message.flags;
     uint8_t* frame_hdr = grpc_slice_buffer_tiny_add(&s->flow_controlled_buffer,
                                                     GRPC_HEADER_SIZE_IN_BYTES);
     frame_hdr[0] = (flags & GRPC_WRITE_INTERNAL_COMPRESS) != 0;

src/core/lib/experiments/experiments.cc

@@ -35,6 +35,11 @@ const char* const description_chaotic_good_legacy_protocol =
 const char* const additional_constraints_chaotic_good_legacy_protocol = "{}";
 const char* const description_client_privacy = "If set, client privacy";
 const char* const additional_constraints_client_privacy = "{}";
+const char* const description_disable_buffer_hint_on_high_memory_pressure =
+    "Disable buffer hint flag parsing in the transport under high memory "
+    "pressure.";
+const char* const
+    additional_constraints_disable_buffer_hint_on_high_memory_pressure = "{}";
 const char* const description_event_engine_application_callbacks =
     "Run application callbacks in EventEngine threads, instead of on the "
     "thread-local ApplicationCallbackExecCtx";
@@ -133,6 +138,10 @@ const ExperimentMetadata g_experiment_metadata[] = {
      true},
     {"client_privacy", description_client_privacy,
      additional_constraints_client_privacy, nullptr, 0, false, false},
+    {"disable_buffer_hint_on_high_memory_pressure",
+     description_disable_buffer_hint_on_high_memory_pressure,
+     additional_constraints_disable_buffer_hint_on_high_memory_pressure,
+     nullptr, 0, false, true},
     {"event_engine_application_callbacks",
      description_event_engine_application_callbacks,
      additional_constraints_event_engine_application_callbacks, nullptr, 0,
@@ -207,6 +216,11 @@ const char* const description_chaotic_good_legacy_protocol =
 const char* const additional_constraints_chaotic_good_legacy_protocol = "{}";
 const char* const description_client_privacy = "If set, client privacy";
 const char* const additional_constraints_client_privacy = "{}";
+const char* const description_disable_buffer_hint_on_high_memory_pressure =
+    "Disable buffer hint flag parsing in the transport under high memory "
+    "pressure.";
+const char* const
+    additional_constraints_disable_buffer_hint_on_high_memory_pressure = "{}";
 const char* const description_event_engine_application_callbacks =
     "Run application callbacks in EventEngine threads, instead of on the "
     "thread-local ApplicationCallbackExecCtx";
@@ -305,6 +319,10 @@ const ExperimentMetadata g_experiment_metadata[] = {
      true},
     {"client_privacy", description_client_privacy,
      additional_constraints_client_privacy, nullptr, 0, false, false},
+    {"disable_buffer_hint_on_high_memory_pressure",
+     description_disable_buffer_hint_on_high_memory_pressure,
+     additional_constraints_disable_buffer_hint_on_high_memory_pressure,
+     nullptr, 0, false, true},
     {"event_engine_application_callbacks",
      description_event_engine_application_callbacks,
      additional_constraints_event_engine_application_callbacks, nullptr, 0,
@@ -379,6 +397,11 @@ const char* const description_chaotic_good_legacy_protocol =
 const char* const additional_constraints_chaotic_good_legacy_protocol = "{}";
 const char* const description_client_privacy = "If set, client privacy";
 const char* const additional_constraints_client_privacy = "{}";
+const char* const description_disable_buffer_hint_on_high_memory_pressure =
+    "Disable buffer hint flag parsing in the transport under high memory "
+    "pressure.";
+const char* const
+    additional_constraints_disable_buffer_hint_on_high_memory_pressure = "{}";
 const char* const description_event_engine_application_callbacks =
     "Run application callbacks in EventEngine threads, instead of on the "
     "thread-local ApplicationCallbackExecCtx";
@@ -477,6 +500,10 @@ const ExperimentMetadata g_experiment_metadata[] = {
      true},
     {"client_privacy", description_client_privacy,
      additional_constraints_client_privacy, nullptr, 0, false, false},
+    {"disable_buffer_hint_on_high_memory_pressure",
+     description_disable_buffer_hint_on_high_memory_pressure,
+     additional_constraints_disable_buffer_hint_on_high_memory_pressure,
+     nullptr, 0, false, true},
     {"event_engine_application_callbacks",
      description_event_engine_application_callbacks,
      additional_constraints_event_engine_application_callbacks, nullptr, 0,

src/core/lib/experiments/experiments.h

@@ -62,6 +62,7 @@ inline bool IsCallTracerInTransportEnabled() { return true; }
 inline bool IsCanaryClientPrivacyEnabled() { return false; }
 inline bool IsChaoticGoodLegacyProtocolEnabled() { return false; }
 inline bool IsClientPrivacyEnabled() { return false; }
+inline bool IsDisableBufferHintOnHighMemoryPressureEnabled() { return false; }
 #define GRPC_EXPERIMENT_IS_INCLUDED_EVENT_ENGINE_APPLICATION_CALLBACKS
 inline bool IsEventEngineApplicationCallbacksEnabled() { return true; }
 #define GRPC_EXPERIMENT_IS_INCLUDED_EVENT_ENGINE_CALLBACK_CQ
@@ -97,6 +98,7 @@ inline bool IsCallTracerInTransportEnabled() { return true; }
 inline bool IsCanaryClientPrivacyEnabled() { return false; }
 inline bool IsChaoticGoodLegacyProtocolEnabled() { return false; }
 inline bool IsClientPrivacyEnabled() { return false; }
+inline bool IsDisableBufferHintOnHighMemoryPressureEnabled() { return false; }
 #define GRPC_EXPERIMENT_IS_INCLUDED_EVENT_ENGINE_APPLICATION_CALLBACKS
 inline bool IsEventEngineApplicationCallbacksEnabled() { return true; }
 #define GRPC_EXPERIMENT_IS_INCLUDED_EVENT_ENGINE_CALLBACK_CQ
@@ -135,6 +137,7 @@ inline bool IsCallTracerInTransportEnabled() { return true; }
 inline bool IsCanaryClientPrivacyEnabled() { return false; }
 inline bool IsChaoticGoodLegacyProtocolEnabled() { return false; }
 inline bool IsClientPrivacyEnabled() { return false; }
+inline bool IsDisableBufferHintOnHighMemoryPressureEnabled() { return false; }
 #define GRPC_EXPERIMENT_IS_INCLUDED_EVENT_ENGINE_APPLICATION_CALLBACKS
 inline bool IsEventEngineApplicationCallbacksEnabled() { return true; }
 #define GRPC_EXPERIMENT_IS_INCLUDED_EVENT_ENGINE_CALLBACK_CQ
@@ -175,6 +178,7 @@ enum ExperimentIds {
   kExperimentIdCanaryClientPrivacy,
   kExperimentIdChaoticGoodLegacyProtocol,
   kExperimentIdClientPrivacy,
+  kExperimentIdDisableBufferHintOnHighMemoryPressure,
   kExperimentIdEventEngineApplicationCallbacks,
   kExperimentIdEventEngineCallbackCq,
   kExperimentIdEventEngineClient,
@@ -215,6 +219,11 @@ inline bool IsChaoticGoodLegacyProtocolEnabled() {
 inline bool IsClientPrivacyEnabled() {
   return IsExperimentEnabled<kExperimentIdClientPrivacy>();
 }
+#define GRPC_EXPERIMENT_IS_INCLUDED_DISABLE_BUFFER_HINT_ON_HIGH_MEMORY_PRESSURE
+inline bool IsDisableBufferHintOnHighMemoryPressureEnabled() {
+  return IsExperimentEnabled<
+      kExperimentIdDisableBufferHintOnHighMemoryPressure>();
+}
 #define GRPC_EXPERIMENT_IS_INCLUDED_EVENT_ENGINE_APPLICATION_CALLBACKS
 inline bool IsEventEngineApplicationCallbacksEnabled() {
   return IsExperimentEnabled<kExperimentIdEventEngineApplicationCallbacks>();

src/core/lib/experiments/experiments.yaml

@@ -64,6 +64,12 @@
   owner: alishananda@google.com
   test_tags: []
   allow_in_fuzzing_config: false
+- name: disable_buffer_hint_on_high_memory_pressure
+  description:
+    Disable buffer hint flag parsing in the transport under high memory pressure.
+  expiry: 2025/03/01
+  owner: vigneshbabu@google.com
+  test_tags: []
 - name: event_engine_application_callbacks
   description: Run application callbacks in EventEngine threads, instead of on the thread-local ApplicationCallbackExecCtx
   expiry: 2025/03/01

src/core/lib/experiments/rollouts.yaml

@@ -53,6 +53,8 @@
     windows: broken
 - name: client_privacy
   default: false
+- name: disable_buffer_hint_on_high_memory_pressure
+  default: false
 - name: event_engine_application_callbacks
   default: true
 - name: event_engine_callback_cq