[heap] Decouple the max semi-space size from the page size

This allows us to change the page size without affecting Scavenger
heuristics and performance.

Bug: chromium:852420
Change-Id: Idcff4296e88e16f9af0ee6ecd00c63d789866fd6
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1499494
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Hannes Payer <hpayer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60028}

src/heap/heap.h

@@ -238,10 +238,11 @@ class Heap {
 #endif
 
   // Semi-space size needs to be a multiple of page size.
-  static const size_t kMinSemiSpaceSizeInKB =
-      1 * kPointerMultiplier * ((1 << kPageSizeBits) / KB);
-  static const size_t kMaxSemiSpaceSizeInKB =
-      16 * kPointerMultiplier * ((1 << kPageSizeBits) / KB);
+  static const size_t kMinSemiSpaceSizeInKB = 512 * kPointerMultiplier;
+  static const size_t kMaxSemiSpaceSizeInKB = 8192 * kPointerMultiplier;
+
+  STATIC_ASSERT(kMinSemiSpaceSizeInKB* KB % (1 << kPageSizeBits) == 0);
+  STATIC_ASSERT(kMaxSemiSpaceSizeInKB* KB % (1 << kPageSizeBits) == 0);
 
   static const int kTraceRingBufferSize = 512;
   static const int kStacktraceBufferSize = 512;

test/unittests/heap/heap-unittest.cc

@@ -20,14 +20,13 @@ typedef TestWithIsolate HeapTest;
 typedef TestWithIsolateAndPointerCompression HeapWithPointerCompressionTest;
 
 TEST(Heap, SemiSpaceSize) {
-  const size_t KB = static_cast<size_t>(i::KB);
   const size_t MB = static_cast<size_t>(i::MB);
   const size_t pm = i::Heap::kPointerMultiplier;
-  ASSERT_EQ(1u * pm * MB / 2, i::Heap::ComputeMaxSemiSpaceSize(0u) * KB);
-  ASSERT_EQ(1u * pm * MB / 2, i::Heap::ComputeMaxSemiSpaceSize(512u * MB) * KB);
-  ASSERT_EQ(2u * pm * MB, i::Heap::ComputeMaxSemiSpaceSize(1024u * MB) * KB);
-  ASSERT_EQ(5u * pm * MB, i::Heap::ComputeMaxSemiSpaceSize(2024u * MB) * KB);
-  ASSERT_EQ(8u * pm * MB, i::Heap::ComputeMaxSemiSpaceSize(4095u * MB) * KB);
+  ASSERT_EQ(512u * pm, i::Heap::ComputeMaxSemiSpaceSize(0u));
+  ASSERT_EQ(512u * pm, i::Heap::ComputeMaxSemiSpaceSize(512u * MB));
+  ASSERT_EQ(2048u * pm, i::Heap::ComputeMaxSemiSpaceSize(1024u * MB));
+  ASSERT_EQ(5120u * pm, i::Heap::ComputeMaxSemiSpaceSize(2024u * MB));
+  ASSERT_EQ(8192u * pm, i::Heap::ComputeMaxSemiSpaceSize(4095u * MB));
 }
 
 TEST_F(HeapTest, ASLR) {