[heap][cleanup] Rename the MemoryAllocator's reservation code_reservation_.

Comments on this reservation indicate it may hold either only code pages or code
and data pages if pointer compression is enabled.  But in fact it only holds the
reservation for code pages.

Change-Id: Ic007fcadf881153b69dce51db561777cc52685bf
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2091465Reviewed-by: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Pierre Langlois <pierre.langlois@arm.com>
Cr-Commit-Position: refs/heads/master@{#66612}

src/heap/spaces.cc

@@ -214,7 +214,7 @@ void MemoryAllocator::InitializeCodePageAllocator(
       NewEvent("CodeRange", reinterpret_cast<void*>(reservation.address()),
                requested));
 
-  heap_reservation_ = std::move(reservation);
+  code_reservation_ = std::move(reservation);
   code_page_allocator_instance_ = std::make_unique<base::BoundedPageAllocator>(
       page_allocator, aligned_base, size,
       static_cast<size_t>(MemoryChunk::kAlignment));

src/heap/spaces.h

@@ -1477,14 +1477,9 @@ class MemoryAllocator {
 
   Isolate* isolate_;
 
-  // This object controls virtual space reserved for V8 heap instance.
-  // Depending on the configuration it may contain the following:
-  // - no reservation (on 32-bit architectures)
-  // - code range reservation used by bounded code page allocator (on 64-bit
-  //   architectures without pointers compression in V8 heap)
-  // - data + code range reservation (on 64-bit architectures with pointers
-  //   compression in V8 heap)
-  VirtualMemory heap_reservation_;
+  // This object controls virtual space reserved for code on the V8 heap. This
+  // is only valid for 64-bit architectures where kRequiresCodeRange.
+  VirtualMemory code_reservation_;
 
   // Page allocator used for allocating data pages. Depending on the
   // configuration it may be a page allocator instance provided by v8::Platform
@@ -1498,7 +1493,7 @@ class MemoryAllocator {
   // can be used for call and jump instructions).
   v8::PageAllocator* code_page_allocator_;
 
-  // A part of the |heap_reservation_| that may contain executable code
+  // A part of the |code_reservation_| that may contain executable code
   // including reserved page with read-write access in the beginning.
   // See details below.
   base::AddressRegion code_range_;
@@ -1507,9 +1502,9 @@ class MemoryAllocator {
   // that controls executable pages allocation. It does not control the
   // optionally existing page in the beginning of the |code_range_|.
   // So, summarizing all above, the following conditions hold:
-  // 1) |heap_reservation_| >= |code_range_|
+  // 1) |code_reservation_| >= |code_range_|
   // 2) |code_range_| >= |optional RW pages| + |code_page_allocator_instance_|.
-  // 3) |heap_reservation_| is AllocatePageSize()-aligned
+  // 3) |code_reservation_| is AllocatePageSize()-aligned
   // 4) |code_page_allocator_instance_| is MemoryChunk::kAlignment-aligned
   // 5) |code_range_| is CommitPageSize()-aligned
   std::unique_ptr<base::BoundedPageAllocator> code_page_allocator_instance_;