Linux Symposium

X-Xen - Hugepage Support in Xen Hypervisor

Aditya Gadre

Huge pages are the memory pages of size 2MB (x86-PAE and x86_64). The number of page walks required for translation from a virtual address to physical 2MB page are reduced as compared to page walks required for translation from a virtual address to physical 4KB page. Also the number of TLB entries per 2MB chunk in memory is reduced by a factor of 512 as compared to 4KB pages. In this way huge pages improve the performance of the applications which perform memory intensive operations. In the context of virtualization, i.e. Xen hypervisor, we propose a design and implementation to support huge pages for paravirtualized guest paging operations.

Our design reserves 2MB pages (MFNs) from the domain's committed memory as per configuration specified before a domain boots. The rest of the memory is continued to be used as 4 KB pages. Thus availability of the huge pages is guaranteed and actual physical huge pages can be provided to the paravirtualized domain. This increases the performance of the applications hosted on the guest operating system which require the huge page support. This design solves the problem of availability of 2MB chunk in guest's physical address space (virtualized) as well as the Xen's physical address space which would otherwise may be unavailable due to fragmentation.

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