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==Huge 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: "[http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.3.2392 Transparent Operating System Support for Superpages]". | 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: "[http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.3.2392 Transparent Operating System Support for Superpages]". | ||
===Linux=== | ===Linux=== | ||
* They were a [http://lwn.net/Articles/40840/ 2003 Kernel Summit] topic | * They were a [http://lwn.net/Articles/40840/ 2003 Kernel Summit] topic, after seeing first [http://kerneltrap.org/node/418 introduction] in Linux 2.5.36 ([http://linuxgazette.net/155/krishnakumar.html LinuxGazette] primer article) | ||
* <tt>get_large_pages(2)</tt> and <tt>shared_large_pages(2)</tt>, as covered in [http://lwn.net/Articles/6969/ this LWN article] | * <tt>alloc_hugepages</tt>, <tt>free_hugepages</tt>, <tt>get_large_pages(2)</tt> and <tt>shared_large_pages(2)</tt>, as covered in [http://lwn.net/Articles/6969/ this LWN article] and present in kernels 2.5.36-2.5.54, were a first attempt to provide explicit large page support to applications. | ||
* [http://www.mjmwired.net/kernel/Documentation/vm/hugetlbpage.txt hugetlbfs] and assorted infrastructure replaced these. Mel Gorman's [http://linux-mm.org/HugePages Linux MM wiki] has a good page on hugetlbfs. | |||
===Applications=== | |||
* [[MySQL]] can use hugetlbfs via the <tt>large-pages</tt> option | |||
* [[kvm]] can use hugetlbfs with the <tt>--mem-path</tt> option since [http://www.linux-kvm.com/content/get-performance-boost-backing-your-kvm-guest-hugetlbfs kvm-62], released in late 2008 | * [[kvm]] can use hugetlbfs with the <tt>--mem-path</tt> option since [http://www.linux-kvm.com/content/get-performance-boost-backing-your-kvm-guest-hugetlbfs kvm-62], released in late 2008 | ||
==Page Clustering== | |||
Page clustering (implemented by [http://lwn.net/Articles/23785/ William Lee Irwin] for Linux in 2003, and not to be confused with page-granularity [http://lwn.net/Articles/297299/ swap-out clustering]). There's good coverage in this [http://kerneltrap.org/node/620 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, "[http://ols.fedoraproject.org/OLS/Reprints.../Reprint-Irwin-OLS2003.pdf A 2.5 Page Clustering Implementation]". | Page clustering (implemented by [http://lwn.net/Articles/23785/ William Lee Irwin] for Linux in 2003, and not to be confused with page-granularity [http://lwn.net/Articles/297299/ swap-out clustering]). There's good coverage in this [http://kerneltrap.org/node/620 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, "[http://ols.fedoraproject.org/OLS/Reprints.../Reprint-Irwin-OLS2003.pdf A 2.5 Page Clustering Implementation]". | ||
Revision as of 05:37, 19 June 2009
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)
- alloc_hugepages, free_hugepages, get_large_pages(2) and shared_large_pages(2), as covered in this LWN article and present in kernels 2.5.36-2.5.54, were a first attempt to provide explicit large page support to applications.
- 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".
