Address space sparsity and fine granularity

Abstract

To fully exploit the potential of large address spaces, e.g. 2 64 -byte, the sparsity problem has to be solved in an efficient manner. Current address translation schemes either cause enormous space overhead (page table trees) or do not support address space structuring, object grouping and mixed page sizes (inverted page tables). Furthermore, an essential handicap of current virtual address spaces is their coarse granularity. It restricts the concept's relevance to low level OS technology. Without this constraint, mapping could be a vertically integrating paradigm, useful on all levels from hardware up to application programming.Guarded page tables help solving both problems. They permit significant extensions of the current programming model without performance degradation: sparse occupation and coarse-grain (4K) pages can be handled by purely conventional hardware; fine-grain (down to 16-byte) pages without fine-grain aliasing become also possible using conventional cache and TLB technology combined with stochastically colored allocation. Unrestricted aliasing and unlimited user level mapping without performance degradation may become possible by hardware innovation.