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Efficient Segment Rounding for Mapped Files

IP.com Disclosure Number: IPCOM000062194D
Original Publication Date: 1986-Oct-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Duvall, KE: AUTHOR [+4]

Abstract

By minimizing Kernel/Virtual Resource Manager (VRM) fault handling operations of existing memory mapped files, improvements in file size overhead and execution time are realized. A file may be mapped Read/Write, Copy-on-Write or Read Only. In these instances, the file is protected by several mechanisms. For files which are opened Read/Write or Copy-on-Write, the following procedure has been implemented for more efficient file handling: 1. The existing file will have an i-size which may not be on a 2K boundary; a segment is created which is rounded up to the next 64K boundary. 2. Rounding down to the closest 2K boundary is performed. All previous pages are not protected initially in the same manner as the rest of the segment in which the last (partial) page is mapped. For example, a 4.

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Efficient Segment Rounding for Mapped Files

By minimizing Kernel/Virtual Resource Manager (VRM) fault handling operations of existing memory mapped files, improvements in file size overhead and execution time are realized. A file may be mapped Read/Write, Copy-on- Write or Read Only. In these instances, the file is protected by several mechanisms. For files which are opened Read/Write or Copy-on-Write, the following procedure has been implemented for more efficient file handling: 1. The existing file will have an i-size which may not be on a 2K boundary; a segment is created which is rounded up to the next 64K boundary. 2. Rounding down to the closest 2K boundary is performed. All previous pages are not protected initially in the same manner as the rest of the segment in which the last (partial) page is mapped. For example, a 4.2K file will cause the creation of a 64K segment. The first two pages of the file (pages 1 and 2, assuming that the file has pages 1-32) will not be protected. The remaining pages (3-32) will be protected Read Only. 3. If a Write is issued to the last page, it is detected that a page is actually mapped in memory, and the file size is modified up to the next 2K boundary. Therefore, the page is unprotected so that the Write operation can be completed successfully. A Copy-on-Write case will be performed in a similar manner. Using this technique, optimal execution time utilization of the directory, kernel and VRM resources for write access fil...