tree 1c62e340994481020c3a508d99d8b3f1169b5a8f
parent 60d7e8f72f4b651d1cc76795057c5ebdbca145e6
author Matthew Dempsky <mdempsky@google.com> 1548379340 +0000
committer commit-bot@chromium.org <commit-bot@chromium.org> 1548379340 +0000

[vm] Implement VirtualMemory::Allocate using AllocateAligned

Instead of implementing separate aligned and unaligned memory
allocation primitives for each OS, just change the unaligned allocator
into a wrapper around the aligned primitive.

While here, we can optimize the AllocateAligned logic slightly: if we
want an N-page-aligned allocation, we only need to increase the
allocation size by N-1 pages instead of N.

Notably, this means 1-page-aligned allocations don't require any extra
alignment pages, so the new logic behaves identically as before on
Android, Fuchsia, Linux, and macOS.

On Windows, it behaves slightly differently only in that unaligned
requests used to be handled as a single VirtualAlloc call with
MEM_RESERVE | MEM_COMMIT, but now they're handled as two separate
calls (reserve *then* commit). Naively, I don't expect this matters in
practice, but if it does, we can always add a fast path for
alignment==page_size_ without affecting the OS-independent API.

Change-Id: I42b2cf5dfc6e137546d8acfb6cc8939a01687948
Reviewed-on: https://dart-review.googlesource.com/c/91081
Commit-Queue: Ryan Macnak <rmacnak@google.com>
Reviewed-by: Ryan Macnak <rmacnak@google.com>