24 research outputs found
FHPM: Fine-grained Huge Page Management For Virtualization
As more data-intensive tasks with large footprints are deployed in virtual
machines (VMs), huge pages are widely used to eliminate the increasing address
translation overhead. However, once the huge page mapping is established, all
the base page regions in the huge page share a single extended page table (EPT)
entry, so that the hypervisor loses awareness of accesses to base page regions.
None of the state-of-the-art solutions can obtain access information at base
page granularity for huge pages. We observe that this can lead to incorrect
decisions by the hypervisor, such as incorrect data placement in a tiered
memory system and unshared base page regions when sharing pages.
This paper proposes FHPM, a fine-grained huge page management for
virtualization without hardware and guest OS modification. FHPM can identify
access information at base page granularity, and dynamically promote and demote
pages. A key insight of FHPM is to redirect the EPT huge page directory entries
(PDEs) to new companion pages so that the MMU can track access information
within huge pages. Then, FHPM can promote and demote pages according to the
current hot page pressure to balance address translation overhead and memory
usage. At the same time, FHPM proposes a VM-friendly page splitting and
collapsing mechanism to avoid extra VM-exits. In combination, FHPM minimizes
the monitoring and management overhead and ensures that the hypervisor gets
fine-grained VM memory accesses to make the proper decision. We apply FHPM to
improve tiered memory management (FHPM-TMM) and to promote page sharing
(FHPM-Share). FHPM-TMM achieves a performance improvement of up to 33% and 61%
over the pure huge page and base page management. FHPM-Share can save 41% more
memory than Ingens, a state-of-the-art page sharing solution, with comparable
performance