Pages

Huge Pages

Making pages larger means fewer TLB misses for a given TLB size (due to more pages being supportable in the same amount of memory, due to narrower page identifiers), large mapping/releasing operations will be faster (due to fewer page table entries needing to be handled), and less memory is devoted to page table entries for a given amount of memory being indexed. The downside is possible wastage of main memory (due to pages not being used as completely). A 2002 paper from Navarro et al at Rice proposed transparent operating system support: "Transparent Operating System Support for Superpages".

Linux

• They were a 2003 Kernel Summit topic, after seeing first introduction in Linux 2.5.36 (LinuxGazette primer article)
• Rohit Seth provided the first explicit large page support to applications as covered in this LWN article
  • alloc_hugepages, free_hugepages, get_large_pages(2) and shared_large_pages(2), present in kernels 2.5.36-2.5.54
• hugetlbfs and assorted infrastructure replaced these. Mel Gorman's Linux MM wiki has a good page on hugetlbfs.

Applications

• MySQL can use hugetlbfs via the large-pages option
• kvm can use hugetlbfs with the --mem-path option since kvm-62, released in late 2008

Page Clustering

Page clustering (implemented by William Lee Irwin for Linux in 2003, and not to be confused with page-granularity swap-out clustering). There's good coverage in this KernelTrap article. This is essentially huge pages without hardware support, and therefore with some overhead and no improvements in TLB-relative performance. It was written up in Irwin's 2003 OLS paper, "A 2.5 Page Clustering Implementation".