Silicon Graphics, Incorporated

Narayanan Ganapathy

Curt F Schimmel

Luis F Stevens

Bhanuprakash Subramanya

A method, system and computer program product for dynamically allocating large memory pages of different sizes. Each process can select multiple page sizes. An algorithm referred to as a &ldquo;Coalescing Daemon&rdquo; is used to allocate large pages. &ldquo;High water marks&rdquo; are specified to the operating system. A high water mark is the maximum percentage of total system memory that the Coalescing Daemon coalesces for a given page size. The high water marks are used to allocate a number of free memory pages for each specified page size. Separate freelists are created and maintained for each page size. Each freelist comprises a linked list of data structures that represent free physical memory pages. A bitmap is set-up by the operating system to represent all memory available to processes. The bitmap is used for determining which memory pages are free during coalescing. The Coalescing Daemon allocates memory pages using a weak, mild and strong coalescing policy. The weak policy is performed first, followed by the mild and the strong policies. The mild and strong policies are performed only if the preceding policy or policies fail. The weak policy searches the bitmap for free contiguous areas of memory and inserts an entry into the associated freelist if found. If the weak policy is unsuccessful, the mild policy attempts to find a suitable chunk of memory which is used to create a contiguous chunk of free memory by migrating busy base pages to other areas. The mild coalescing policy searches the bitmap for a chunk of memory in which the set bits (i.e. the free base pages) are above a tunable predetermined threshold value. Thus, a limited amout of migration is performed according to predetermined threshold. If the mild coalescing policy fails the strong coalescing policy is performed. In the strong coalescing policy, base pages are migrated to create a free chunk, regardless of a threshold amount.

Method, system and computer program product for dynamically allocating large memory pages of different sizes

A system, method and computer program product for virtual memory support for TLBs with multiple page sizes that require only minor revisions to existing operating system code and remains compatible with existing applications. The virtual memory support provided herein is transparent to many existing operating system procedures and application programs. Various page sizes such as 4 KB, 64 KB, 256 KB, 1 MB, 4 MB and 16 MB page sizes can be used by application programs and each process can use multiple page sizes. Base page sized PTEs and data structures associated with physical pages (PFDATs) are maintained. Maintaining PFDATs and PTEs at a base page level facilitates upgrading and downgrading of memory pages. In addition, different processes can have different views of the same data. Support is provided for upgrading and downgrading memory pages. Examples of operating system methods that can be used for virtual memory support for multiple page sized TLBs are provided herein. Such examples include downgrading and upgrading memory pages, large page faulting and prefaulting, large page validation and page table entry setup.

Method, system and computer program product for virtual memory support

A system, method and computer program product for reverse mapping a page of memory to one or more data structure references, such as page table entries, that reference the page of memory. A number m of fields of a page frame data structure are reserved for storing reverse mapping data for a page of memory. Each reserved field can store a reverse map entry for pointing to a data structure reference, such as a page table entry, that references the page of memory that is represented by the page frame data structure. Where a number n of references to the page of memory is greater than the number m of reserved fields, a reverse map table is generated for storing additional reverse map entries. When a reverse map table is generated, one of the reverse map entries in one of the reserved fields of the page frame data structure is moved to the reverse map table. A pointer to the reverse map table is placed in the now-vacant reserved field. Indexes in the page table entries are used to identify and remove the reverse map entries when a page table is deallocated. Reverse map tables can be generated as needed and can be dynamically sized to accommodate any number of reverse map entries.

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San Jose, CA, United States of America

Narayanan Ganapathy