  Modern GPUs face a trade-off on how the page size used for memory management
affects address translation and demand paging. Support for multiple page sizes
can help relax the page size trade-off so that address translation and demand
paging optimizations work together synergistically. However, existing page
coalescing and splintering policies require costly base page migrations that
undermine the benefits multiple page sizes provide. In this paper, we observe
that GPGPU applications present an opportunity to support multiple page sizes
without costly data migration, as the applications perform most of their memory
allocation en masse (i.e., they allocate a large number of base pages at once).
We show that this en masse allocation allows us to create intelligent memory
allocation policies which ensure that base pages that are contiguous in virtual
memory are allocated to contiguous physical memory pages. As a result,
coalescing and splintering operations no longer need to migrate base pages.
  We introduce Mosaic, a GPU memory manager that provides
application-transparent support for multiple page sizes. Mosaic uses base pages
to transfer data over the system I/O bus, and allocates physical memory in a
way that (1) preserves base page contiguity and (2) ensures that a large page
frame contains pages from only a single memory protection domain. This
mechanism allows the TLB to use large pages, reducing address translation
overhead. During data transfer, this mechanism enables the GPU to transfer only
the base pages that are needed by the application over the system I/O bus,
keeping demand paging overhead low.
