Reland [partition_alloc] Allow 2 GiB direct mapped allocations.

- Raises the limit of direct mapped allocations. WASM needs
  to be able to allocate 2GiB regions.

Bug: chromium:801604
Change-Id: I77e905ff4ae6f5ca66de9daf30f19bb6f7b54089
Reviewed-on: https://chromium-review.googlesource.com/875301Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Bill Budge <bbudge@chromium.org>
Cr-Commit-Position: refs/heads/master@{#530380}

base/allocator/partition_allocator/partition_alloc.cc

@@ -34,6 +34,9 @@ static_assert(sizeof(base::PartitionSuperPageExtentEntry) <=
 static_assert(base::kPageMetadataSize * base::kNumPartitionPagesPerSuperPage <=
                   base::kSystemPageSize,
               "page metadata fits in hole");
+// Limit to prevent callers accidentally overflowing an int size.
+static_assert(base::kGenericMaxDirectMapped <= 1UL << 31,
+              "maximum direct mapped allocation");
 // Check that some of our zanier calculations worked out as expected.
 static_assert(base::kGenericSmallestBucket == 8, "generic smallest bucket");
 static_assert(base::kGenericMaxBucketed == 983040, "generic max bucketed");

base/allocator/partition_allocator/partition_alloc.h

@@ -206,7 +206,7 @@ static const size_t kGenericMaxBucketed =
 static const size_t kGenericMinDirectMappedDownsize =
     kGenericMaxBucketed +
     1;  // Limit when downsizing a direct mapping using realloc().
-static const size_t kGenericMaxDirectMapped = INT_MAX - kSystemPageSize;
+static const size_t kGenericMaxDirectMapped = 1UL << 31;  // 2 GiB
 static const size_t kBitsPerSizeT = sizeof(void*) * CHAR_BIT;
 
 // Constants for the memory reclaim logic.

base/allocator/partition_allocator/partition_alloc_unittest.cc

@@ -859,7 +859,7 @@ TEST_F(PartitionAllocTest, GenericAllocGetSize) {
   }
 
   // Too large allocation.
-  requested_size = INT_MAX;
+  requested_size = (1UL << 31) + 1;
   predicted_size = generic_allocator.root()->ActualSize(requested_size);
   EXPECT_EQ(requested_size, predicted_size);
 }