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Browse Prior Art Database

Translate Look-Aside Buffer Usage in a File System With Virtual Addressing

IP.com Disclosure Number: IPCOM000119835D
Original Publication Date: 1991-Mar-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 2 page(s) / 89K

Publishing Venue

IBM

Related People

Barton, J: AUTHOR [+9]

Abstract

Disclosed is the method and use of a Translation Look-Aside Buffer for a file system that uses relocatable storage addresses for file objects on DASD.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Translate Look-Aside Buffer Usage in a File System With Virtual Addressing

      Disclosed is the method and use of a Translation
Look-Aside Buffer for a file system that uses relocatable storage
addresses for file objects on DASD.

      Traditional file systems support relative byte offset, relative
record offset, or key addressing to reference file data.  These
values are then calculated to physical device location, either via
hashing algorithm or direct pointers. In a file system where the
relative record or relative byte or key value result in a "virtual
file address," a second level of translation is required to translate
the virtual address to a real address (disk address).

      RELOCATION DIRECTORIES

      In a file system whose addresses are treated much like virtual
addressing in virtual operating systems, a technique of associating a
virtual address to a real address is used. Relocation directories,
stored on disk, are used to translate virtual to real addresses.
Whenever a reference to a file object is made, a translation is
required.  The relocation directories are brought into main storage,
and the file reference is resolved.  The overhead related to
translating virtual disk addresses to real disk addresses is
unacceptable in terms of performance.  The additional I/O required to
read the relocation directories each time a file reference is made
can be eliminated by caching successful translations in a Translation
Look-Aside Buffer (TLB) which is cached in CPU main storage.

      The buffer is sub-divided into virtual data groups. Only those
virtual data groups that are referenced have entries in the TLB. For
this disclosure, we will call the data groups "data segments."  These
data segments have a length of 256 4K pages or 1 megabyte.

      Whenever a translation is performed, a complete virtual data
segment is translated.  The assumption is that if a virtual data
segment is referenced once, it is very likely that other virtual data
pages in the virtual data segment will be referenced.  This avoids a
piecemeal translation of virtual data segments, and further optimizes
external storage references.

      CONSISTENT TRANSLATION WITH MULTI-SYSTEM SHA...