topic Re: Bus addressable memory in Operating System - OpenVMS

Bus addressable memory

Wim Van den Wyngaert — Tue, 21 Jun 2005 10:09:18 GMT

Anyone an idea what it is used for ?
I have 1 node running 8.2 that has allocated zero bytes for it.

Wim

Re: Bus addressable memory

Volker Halle — Tue, 21 Jun 2005 10:22:16 GMT

Wim,

there are certain IO adapters (CIPCA, CIXCD, KFMSB, and Qlogic 1020ISP), that are limited in addressing physical memory beyond 1GB or 4GB. To overcome this restriction, some data structures used by those adapters have to be allocated in BAP pool (Bus Adressable Pool), which will be configured to reside in physical memory at addresses lower than 1 or 4 GB.

http://h71000.www7.hp.com/doc/73final/6017/6017pro_070.html

The NPAG_BAP_* parameters control this pool.

Volker.

Re: Bus addressable memory

Wim Van den Wyngaert — Tue, 21 Jun 2005 10:52:19 GMT

It seems that autogen put the npag_bap_min and max on 0 when it was standalone but still used something. When I clustered the station with 7.3 nothing was used. I now did an autogen and rebooted and it is using 110 K of the maximum of 128 K (which is npag_bap_max).

Wim

Re: Bus addressable memory

Ian Miller. — Tue, 21 Jun 2005 11:26:02 GMT

because non-paged pool can reach to addresses that some adapaters can not handle (as Volker mentioned) then a seperate pool is created (BAP) which is always placed where it can be accessed by any adaptor. It gets created as a seperate pool by AUTOGEN setting the system paramters to non-zero values if your non-paged pool becomes big enough so that some of it may be in parts of the address space that some adaptors can not access.

Re: Bus addressable memory

Wim Van den Wyngaert — Tue, 21 Jun 2005 15:01:47 GMT

Ian & Volker,

This concerns an AS500 with 128 MB and 512 MB pagefile. Why does it need those structures ? For the disk of 2 GB ?

Wim

Re: Bus addressable memory

Volker Halle — Wed, 22 Jun 2005 00:49:15 GMT

Wim,

I'm seeing similar results on an AlphaServer 1000A V8.2 with 128 MB memory. BAP pool is 128 KB with 17.1 KB used. This system has 2 Qlogic ISP1020 SCSI-2 adapters (see SDA> CLUE CONFIG).

This has nothing to do with disk size or such. Some IO adapters (plugged into PCI or XMI buses) just can't handle 'high' physical memory addresses and as they sometimes need to allocate datastructures from nonpaged pool, the operating system needs to provide bus adressable pool mapped to 'lower' physical addresses.

Use SDA> SHOW POOL/BAP/HEADER to see, which data structures are allocated in BAP pool.

Volker.

Re: Bus addressable memory

Wim Van den Wyngaert — Wed, 22 Jun 2005 01:40:49 GMT

Volker,

OK but what did it do when the usage was zero ? Live without it ?

Wim

Re: Bus addressable memory

Volker Halle — Wed, 22 Jun 2005 02:40:39 GMT

Wim,

with 128 MB of memory, there should be no problem for the IO adapter (assumimg you also have a Qlogic ISP 1020) to address all of physical memory. If there is no BAP, datastructures (for this adapter) would then be allocated from normal nonpaged pool.

Use SEARCH SYS$SYSTEM:AGEN$FEEDBACK.DAT BAP to see which values of BAP AUTOGEN feedback is suggesting.

You can certainly override the NPAG_BAP_* values to prevent BAP pool from being created in this kind of config.

Volker.