Browse Prior Art Database

Large Pages Using Power PC BATs

IP.com Disclosure Number: IPCOM000123196D
Original Publication Date: 1998-Jun-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 1 page(s) / 35K

Publishing Venue

IBM

Related People

Melaey, BG: AUTHOR [+2]

Abstract

A method to use PowerPC BATs to simulate large pages. This mechanism minimizes changes to the operating systems.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 86% of the total text.

Large Pages Using Power PC BATs

   A method to use PowerPC BATs to simulate large
pages.  This mechanism minimizes changes to the operating systems.

   On large servers, database applications tend to use very
large address spaces.  The address spaces tend to be many times
larger than the number of translation lookaside entries (TLBs) in
the hardware which manage the translation from virtual addresses to
physical addresses.  When the number of pages used becomes much
larger than the number of TLB's available, the system slows down as
translation misses occur.

   The PowerPC architecture includes a number of mechanisms
for virtual to physical translation.  One of them is block address
translation (BAT).  This mechanism allows translation of contiguous
virtual addresses without the use of the TLB.  The mechanism
requires that the pages managed by the BAT are not also managed by
the TLB.  Thus, pages mapped by BAT are typically pinned in memory
(not paged by the AIX virtual memory manager).  Because they are not
managed as typical pages, AIX I/O routines do not allow access to the
pages.

   The invention is to take contiguous physical memory and
make it into logical 'large pages'.  Since a BAT may map up to 256
megabytes of storage, we can use the available BAT's to create some
number of 256 MByte 'pages'.  The 'pages' need to be mapped to AIX
segments which, while not managing the storage as typically is done
in AIX likely by mapping each page in the segment w...