class VirtualAlloc

Allocator needs to be told what state to set any allocated pages to. This allows for using the

allocator as a heap or generic allocator for an object.

Initialize the allocator and make it ready for use. Takes a a virtual address range as a base

and size in bytes. These both must be page aligned and there must be no pages mapped into the

hardware page tables for this range.

|alloc_guard| is the minimum number of virtual pages to place between two allocations and

serve as guard pages. Any reads or writes that over or under run an allocation into the padding

will trigger an immediate hardware page fault.

Returns the number of pages allocated to provide the bitmap for tracking allocations. Exposed

as a debug named function as there is no promise that it has to be a bitmap for tracking and

this interface is likely to change and should only be used for debugging.

AllocPages can only be called after after a successful Init call, otherwise it will return an

error. Number of pages requested must be non zero.

Returns a non-zero number of pages at the given virtual address. Partial frees are supported

such that if 2 pages were allocated at X it is allowed to FreePages(X, 1) and separately

FreePages(X + kPageSize, 1).

Returns whether or not the allocator will attempt to optimize large allocations with

contiguous allocations and mappings that can get promoted to large pages. It does not guarantee

that it will succeed at doing this though.

Frees any allocated pages as if FreePages had been called on every outstanding allocation. This

is exposed for testing for circumstances where externally tracking every allocations is

burdensome and not the goal of the test.

Force allocates the given range, overriding any padding or alignment requirements. This is used

for testing to more precisely control available allocation regions. Panics if range is invalid

or already allocated.