e1ac50c0 marks temporary buffers as volatile, but it only mlocks() them for the duration
of memcpy() of initial data, leaving Metal runtime a window to snatch it before the buffer
is no longer in use. Simply putting the munlock() in a completion handler raises questions
about possible edge cases where multiple, non page-aligned allocations are live.
This patch fixes it by keeping the whole buffer non-volatile while is supports any active
allocations.
Fixes rendering issues in Sekiro: Shadows Die Twice menus.
c9d425a37b