efi: Make the heap size more reasonable

When booting a VM with 512MiB assigned to it almost half was being lost
to the heap allocator and the amount of heap allocations that the
firmware does should easily fit into the new 2MiB limit.

Signed-off-by: Rob Bradford <[email protected]>

Author: rbradford

src/efi/mod.rs

@@ -924,7 +924,7 @@ fn extract_path(device_path: &DevicePathProtocol, path: &mut [u8]) {
 }
 
 const PAGE_SIZE: u64 = 4096;
-const HEAP_SIZE: usize = 256 * 1024 * 1024;
+const HEAP_SIZE: usize = 2 << 20; /* 2MiB */
 
 // Populate allocator from E820, fixed ranges for the firmware and the loaded binary.
 fn populate_allocator(info: &dyn bootinfo::Info, image_address: u64, image_size: u64) {