Kernel Memory Allocation

ManualsBrandsHP ManualsSoftwareHP-UX vPars and Integrity VM v6

How kernel memory is allocated and may be

controlled in a vPar PA-RISC environment

Version 3.0 4/16/08

I. Introduction

This white paper provides an explanation on how HP-UX Virtual Partitions (vPars) running on PA-RISC

architecture reserve/allocate memory. Specifically, it attempts to explain the allocation of the lower 2GB of

memory address space and the rules for its use. This is not intended to replace the existing customer

viewable document titled “Installing and Managing HP-UX Virtual Partitions” on the

http://docs.hp.com

website. This is intended to explain how you can explicitly specify memory

addresses/ranges in order to overcome the problems of running out of kernel space.

II. The “Rule” or Limitation

The PA-RISC HP-UX kernel is required to be loaded into memory below 2GB and be contiguous because

some heavily accessed low-level machine code kernel routines were written with 32-bit displacements in

order to preserve performance relative to the 32-bit version of HP-UX. There are currently no plans to

change this on PA-RISC. On the Itanium version of HP-UX there is no such optimization so kernels can be

loaded anywhere in memory. Therefore, Itanium servers with the Integrity HP-UX kernel are not required to

be loaded into memory below 2GB.

This PA-RISC HP-UX Kernel requirement also applies in a Virtual Partitions environment with the addition that

ALL vPars kernels’ text and data (added together) must fit under the 2GB lower address space and each

kernel must reside in contiguous memory. This restriction usually isn't a problem unless you significantly

increase some of the tunable parameters that affect the data segment. As the vPar monitor is loading

kernels (booting vPars), if one or more of the kernels won’t fit, the load will fail with a message like this in

the monitor log:

INFO:CPU2:MON:No error free contiguous memory in the system to load the kernel below 2GB

So, in summary, all PA-RISC HP-UX vPar kernels added together must not only fit within the lower 2GB

address space but each kernel must reside in contiguous memory as well. This requirement does not apply

to Integrity HP-UX vPar kernels and for the rest of this document any reference to “kernel” only apples to the

PA-RISC (not Integrity) kernel.

Also note that vPars A.03 has a fixed 64MB memory “granularity”. vPars A.04 and A.05 have a user

defineable memory granularity. All references in this document to 64MB chuncks are refering to the fixed

vPars A.03 memory granularity but may be adjusted for a vPars A.04/A.05 user defined granularity.

Alan Hymes, Solution Architect, America’s Presales

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Summary of content (5 pages)

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How kernel memory is allocated and may be controlled in a vPar PA-RISC environment 1 Version 3.0 I. 4/16/08 Introduction This white paper provides an explanation on how HP-UX Virtual Partitions (vPars) running on PA-RISC architecture reserve/allocate memory. Specifically, it attempts to explain the allocation of the lower 2GB of memory address space and the rules for its use.
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How kernel memory is allocated and may be controlled in a vPar PA-RISC environment III. How the Virtual Partition Monitor allocates memory As each vPar's kernel is loaded, the monitor will first look at the kernel size and in 64MB chunks with vPars A.03 and in whatever the granularity size is with vPars A.04 and A.05, allocate memory from the lower 2GB address space. The monitor will then allocate the rest of the requested memory for the vPar from the upper memory address space.
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How kernel memory is allocated and may be controlled in a vPar PA-RISC environment 1. If the change in size of the kernel does not cross a 64MB boundry, when the monitor loads the new kernel (ie. on reboot of the vPar) it will load the new kernel back into the same spot. Or at the very least it may not be the same spot but you are guaranteed that it will fit because the size hasn’t crossed another 64MB boundry and the vPar owned enough lower 2GB address space originally. 2.
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How kernel memory is allocated and may be controlled in a vPar PA-RISC environment A. Initially creating vPars Create each vPar defining the base and range of memory to be some value that you are sure the kernel will not grow beyond. For example, if the current kernel is using 192MB of contiguous space, then specify a range of 256MB or whatever you think the kernel could possibly grow to in 64MB chunks.
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How kernel memory is allocated and may be controlled in a vPar PA-RISC environment 4096 - (2048-768) = 2816 2816 = vpar_mem_max which is the user assignable memory allowed which leaves 4096 – 2816 = 1184 MB in the lower 2GB free By using this process, as long as all of your kernels don’t use up all of the lower 2GB address space, then you will always have the maximum lower 2GB address space free to either extend existing vPar kernels or add new vPars.