heap: Move headroom for allocation behind --random-gc-interval

Keep --gc-interval precise wrt to the # of allocations needed for a
GC.

Bug: v8:12615
Change-Id: I1ff45ef709013427b5f27643e3a6135dd0f4025d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3485676Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79256}

src/heap/heap-allocator.cc

@@ -141,30 +141,20 @@ void HeapAllocator::SetAllocationTimeout(int allocation_timeout) {
 }
 
 void HeapAllocator::UpdateAllocationTimeout() {
-  if (FLAG_random_gc_interval <= 0 && FLAG_gc_interval < 0) return;
-
-  int new_timeout;
   if (FLAG_random_gc_interval > 0) {
-    new_timeout = allocation_timeout_ <= 0
+    const int new_timeout = allocation_timeout_ <= 0
                                 ? heap_->isolate()->fuzzer_rng()->NextInt(
                                       FLAG_random_gc_interval + 1)
                                 : allocation_timeout_;
-
-  } else {
-    DCHECK_GE(FLAG_gc_interval, 0);
-    new_timeout = FLAG_gc_interval;
-  }
-  DCHECK_GE(new_timeout, 0);
-
     // Reset the allocation timeout, but make sure to allow at least a few
     // allocations after a collection. The reason for this is that we have a lot
-  // of allocation sequences and we assume that a garbage collection will allow
-  // the subsequent allocation attempts to go through.
-  //
-  // TODO(v8:12615): Move `kFewAllocationsHeadroom` behind
-  // `FLAG_random_gc_interval`.
+    // of allocation sequences and we assume that a garbage collection will
+    // allow the subsequent allocation attempts to go through.
     constexpr int kFewAllocationsHeadroom = 6;
     allocation_timeout_ = std::max(kFewAllocationsHeadroom, new_timeout);
+  } else if (FLAG_gc_interval >= 0) {
+    allocation_timeout_ = FLAG_gc_interval;
+  }
 }
 
 #endif  // V8_ENABLE_ALLOCATION_TIMEOUT

test/mjsunit/regress/regress-1000635.js

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
-// Flags: --stress-compaction --detailed-error-stack-trace --gc-interval=1
+// Flags: --stress-compaction --detailed-error-stack-trace --gc-interval=6
 
 function add(a, b) {
   throw new Error();