tor-browser

commit 0a701bae96dfbea8212f8a34490341535f67a9f0
parent 45290297179b465ddf1a2d1cd098f3946ecb56af
Author: Jan de Mooij <jdemooij@mozilla.com>
Date:   Mon,  5 Jan 2026 16:12:23 +0000

Bug 2002938 - Start source compression tasks less eagerly on non-shrinking GCs. r=jonco

This patch changes the heuristics so that pending compression tasks are immediately
started on shrinking GCs. For non-shrinking GCs it increases the delay from `gcNumber + 1`
to `gcNumber + 3`.

This reduces the number of compression tasks and compressed script sources on a full
Speedometer 3 run, and moves more of the compression tasks to shrinking GCs.

Differential Revision: https://phabricator.services.mozilla.com/D274387

Diffstat:
M
js/src/gc/GC.cpp
 | 
2
+-
M
js/src/vm/HelperThreadState.h
 | 
2
+-
M
js/src/vm/HelperThreads.cpp
 | 
18
+++++++++++-------
M
js/src/vm/HelperThreads.h
 | 
2
+-

4 files changed, 14 insertions(+), 10 deletions(-)
diff --git a/js/src/gc/GC.cpp b/js/src/gc/GC.cpp
@@ -2895,7 +2895,7 @@ bool GCRuntime::beginPreparePhase(JS::GCReason reason, AutoGCSession& session) {
    * GCReason::XPCONNECT_SHUTDOWN GCs we can remove the extra check.
    */
   if (!isShutdownGC() && reason != JS::GCReason::XPCONNECT_SHUTDOWN) {
-    StartOffThreadCompressionsOnGC(rt);
+    StartOffThreadCompressionsOnGC(rt, isShrinkingGC());
   }
 
   return true;
diff --git a/js/src/vm/HelperThreadState.h b/js/src/vm/HelperThreadState.h
@@ -430,7 +430,7 @@ class GlobalHelperThreadState {
 
  public:
   // Used by a major GC to create and enqueue compression tasks.
-  enum class ScheduleCompressionTask { GC, API };
+  enum class ScheduleCompressionTask { NonShrinkingGC, ShrinkingGC, API };
   void createAndSubmitCompressionTasks(ScheduleCompressionTask schedule,
                                        JSRuntime* rt);
 
diff --git a/js/src/vm/HelperThreads.cpp b/js/src/vm/HelperThreads.cpp
@@ -1637,10 +1637,10 @@ void GlobalHelperThreadState::createAndSubmitCompressionTasks(
       return true;
     }
 
-    // If we're starting tasks on GC, we wait 2 major GCs to start compressing
-    // in order to avoid immediate compression.
-    if (schedule == ScheduleCompressionTask::GC &&
-        rt->gc.majorGCCount() <= entry.majorGCNumber() + 1) {
+    // If we're starting tasks on a non-shrinking GC, we wait a few major GCs to
+    // start compressing in order to avoid immediate compression.
+    if (schedule == ScheduleCompressionTask::NonShrinkingGC &&
+        rt->gc.majorGCCount() <= entry.majorGCNumber() + 3) {
       return false;
     }
 
@@ -1722,9 +1722,13 @@ void GlobalHelperThreadState::runPendingSourceCompressions(JSRuntime* runtime) {
   AttachFinishedCompressions(runtime, lock);
 }
 
-void js::StartOffThreadCompressionsOnGC(JSRuntime* runtime) {
-  HelperThreadState().createAndSubmitCompressionTasks(
-      GlobalHelperThreadState::ScheduleCompressionTask::GC, runtime);
+void js::StartOffThreadCompressionsOnGC(JSRuntime* runtime,
+                                        bool isShrinkingGC) {
+  auto schedule =
+      isShrinkingGC
+          ? GlobalHelperThreadState::ScheduleCompressionTask::ShrinkingGC
+          : GlobalHelperThreadState::ScheduleCompressionTask::NonShrinkingGC;
+  HelperThreadState().createAndSubmitCompressionTasks(schedule, runtime);
 }
 
 template <typename T>
diff --git a/js/src/vm/HelperThreads.h b/js/src/vm/HelperThreads.h
@@ -307,7 +307,7 @@ void WaitForAllHelperThreads(AutoLockHelperThreadState& lock);
 
 // Start handling any compression tasks for this runtime. Called at the start of
 // major GC.
-void StartOffThreadCompressionsOnGC(JSRuntime* rt);
+void StartOffThreadCompressionsOnGC(JSRuntime* rt, bool isShrinkingGC);
 
 // Cancel all scheduled, in progress, or finished compression tasks for
 // runtime.