IBM Power System POWER7 Series, Optimization And Tuning Manual

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POWER7 and Optimization and Tuning Guide
While 16 MB and 16 GB pages are intended only for particularly high performance
environments, 64 KB pages are considered general purpose, and most workloads benefit
from using 64 KB pages rather than 4 KB pages.
Multipage size support on Linux
On Power Systems running Linux, the default page size is 64 KB, so most, but not all,
applications are expected to see a performance benefit from this default. There are cases in
which an application uses many small files, which can mean that each file is loaded into a
64 KB page, resulting in poor memory utilization.
Support for 16 MB pages (
hugepages
in Linux terminology) is available through various
mechanisms and is typically used for databases, Java engines, and high-performance
computing (HPC) applications. The libhugetlbfs package is available in Linux distributions,
and using this package gives you the most benefit from 16 MB pages.
Multipage size support on AIX
The pagesize -a command on AIX determines all of the page sizes that are supported by AIX
on a particular system.
IBM AIX 5L™ Version 5.3 with the 5300-04 Technology Level supports up to four different
page sizes, but the actual page sizes that are supported by a particular system vary, based
on processor chip type.
AIX V6.1 supports segments with two page sizes: 4 KB and 64 KB. By default, processes use
these variable page size segments. This configuration is overridden by the existing page size
selection mechanism. Page sizes are an attribute of an individual segment (whether single
page size or mixed per segment). A process address space can consist of a mix of segments
of varying page sizes. For example, the process text segment can be 4 KB pages, and its
stack and heap segments can be 64 KB page size segments.
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Because the 64 KB page size is easy to use, and because it is expected that many
applications perform better when they use the 64 KB page size rather than the 4 KB page
size, AIX has rich support for the 64 KB page size. No system configuration changes are
necessary to enable a system to use the 64 KB page size. On systems that support the 64 KB
page size, the AIX kernel automatically configures the system to use it. Table 2-3 and
Table 2-4 on page 27 list the page size specifications for Power Systems.
Table 2-3 Page size support for Power HW and AIX configuration support
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Multiple page size support, available at:
http://pic.dhe.ibm.com/infocenter/aix/v7r1/topic/com.ibm.aix.prftungd/doc/prftungd/multiple_page_siz
e_support.htm
Page size Required hardware Requires user configuration Restricted
4 KB ALL No No
64 KB or later No No
16 MB POWER4 or later Yes Yes
16 GB or later Yes Yes
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