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Method for managing concurrent access to virtual memory data structures
| Details |
Inventors: Schimmel, Curt F.;
Assignee: Silicon Graphics, Inc. (Mountain View, CA)
Primary Examiner: Kim; Matthew
Assistant Examiner: Anderson; Matthew D.
Attorney, Agent or Firm: Schwegman, Lundberg, Woessner & Kluth, P.A.
In a method for providing concurrent access to virtual memory data structures, a lock bit for locking a virtual page data structure is provided in a page table entry of a page table. The page table is configured to map virtual pages to physical pages. Then, a first thread specifying an operation on the virtual page data structure is received. The first thread is provided exclusive access to the virtual page data structure by setting the lock bit in the page table entry such that other threads are prevented from accessing the virtual page data structure. A wait bit also may be provided in the page table entry to indicate that one or more of the other threads are in a wait queue when the first thread has exclusive access to the data structure. When the first thread no longer needs exclusive access to the data structure, a second thread is selected from among the other threads and is provided with exclusive access to the data structure. |
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DETAILED DESCRIPTION Broadly speaking, the present invention fills these needs by providing methods for managing concurrent access to the kernel data structures for a virtual page in memory.
It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device, a method, or a computer readable medium.
Several inventive embodiments of the present invention are described below.
The present invention provides methods for providing concurrent access to a virtual page data structure in a computer system.
A lock bit for locking a virtual page data structure is provided in a page table entry of a page table.
The page table is configured to map virtual pages to physical pages.
Then, a first thread specifying an operation on the virtual page data structure is received.
The first thread is provided exclusive access to the virtual page data structure by setting the lock bit in the page table entry such that other threads are prevented from accessing the virtual page data structure.
Preferably, a wait bit also is provided in the page table entry to indicate that one or more of the other threads are in a wait queue when the first thread has exclusive access to the page.
When the first thread no longer needs exclusive access to the page, a second thread is selected from among the other threads and is provided with exclusive access to the page.
Alternatively, the waiting threads may be placed in a spin loop to wait for the lock bit to become available.
In this case, the wait bit need not be used.
By thus providing a lock in each page table entry, the present invention allows the locks to scale on a one-to-one basis with page table entries and therefore with virtual pages as well.
Furthermore, the methods of the present invention employ a single lock bit in each of the existing page table entries, thereby substantially reducing space requirements and eliminating the need for additional data structures.
The use of a wait bit in the page table entry facilitates efficient locking when more than one thread is waiting to access a data structure associated with the page table entry
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