[sandbox] Shrink sandbox on Android to 128GB

The majority of 64-bit Android devices appear to be using a 40-bit
address space, i.e. 512GB for userspace. Allocating a 256GB sandbox
(plus 2x 32GB guard regions) may take too much of the address space and
cause the creation of other address space reservations (e.g. the cppgc
caged heap), which are created per worker, to fail later on.

In general, we should try to limit the sandbox size to less than 1/4 of
the address space, so this CL shinks the sandbox on Android to 128GB.

Bug: chromium:1327131
Change-Id: Ib48b45506ad6a7a5e15b95115c7642bf62a68fa1
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3652783Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Samuel Groß <saelo@chromium.org>
Cr-Commit-Position: refs/heads/main@{#80636}

include/v8-internal.h

@@ -188,7 +188,15 @@ using ExternalPointer_t = Address;
 #ifdef V8_ENABLE_SANDBOX
 
 // Size of the sandbox, excluding the guard regions surrounding it.
+#ifdef V8_OS_ANDROID
+// On Android, most 64-bit devices seem to be configured with only 39 bits of
+// virtual address space for userspace. As such, limit the sandbox to 128GB (a
+// quarter of the total available address space).
+constexpr size_t kSandboxSizeLog2 = 37;  // 128 GB
+#else
+// Everywhere else use a 1TB sandbox.
 constexpr size_t kSandboxSizeLog2 = 40;  // 1 TB
+#endif  // V8_OS_ANDROID
 constexpr size_t kSandboxSize = 1ULL << kSandboxSizeLog2;
 
 // Required alignment of the sandbox. For simplicity, we require the