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The Question is:
Dear Wizard,
I have a memroy-mapped file ($crmpsc, global section, mapped into the P0
address space) which is 6714 pages (of 8K size each) on an Alpha running
OpenVMS V7.1-2. I am using this as a store for several balanced binary-trees,
which will be accessed by sever
al jobs.
I am in a process of making some modifications to this global section to store
more information. This certainly needs an increase in the size of the global
section. It will grow upto 5 or 6 times its current size! But, if we increase
the size of the globa
l section, there will definitely be some impact on the system resources and
hence the performance. (This is a real-time system).
Any suggestions or thoughts?
Also, how do I calculate the optimum value for the GBLPAGES parameter?
Here are some information about my system:
------------------------------------------
$SHOW CPU
<My Machine>, a AlphaServer DS20 500 MHz
Multiprocessing is ENABLED. Streamlined synchronization image loaded.
Minimum multiprocessing revision levels: CPU = 1
PRIMARY CPU = 00
Active CPUs: 00
Configured CPUs: 00 01
$SHOW MEMORY
System Memory Resources on 24-MAR-2000 10:56:16.67
Physical Memory Usage (pages): Total Free In Use Modified
Main Memory (2176.00Mb) 278528 184980 87962 5586
Virtual I/O Cache (Kbytes): Total Free In Use
Cache Memory 3200 504 2696
Granularity Hint Regions (pages): Total Free In Use Released
Execlet code region 512 0 373 139
Execlet data region 80 1 79 0
S0/S1 Executive data region 641 0 641 0
S2 Executive data region 1360 0 1360 0
Resident image code region 1024 0 320 704
Slot Usage (slots): Total Free Resident Swapped
Process Entry Slots 221 158 63 0
Balance Set Slots 219 158 61 0
Dynamic Memory Usage (bytes): Total Free In Use Largest
Nonpaged Dynamic Memory 10231808 6382848 3848960 2880640
Paged Dynamic Memory 2686976 1028544 1658432 1000736
Buffer Object Usage (pages): In Use Peak
32-bit System Space Windows (S0/S1) 0 3
64-bit System Space Windows (S2) 0 0
Memory Reservations (pages): Reserved In Use Type
Total (0 Mb reserved) 0 0
Paging File Usage (blocks): Free Reservable Total
DISK$<My Node>_V71-2:[SYS0.SYSEXE]SWAPFILE.SYS
28288 28288 28288
DISK$<My Node>_V71-2:[SYS0.SYSEXE]PAGEFILE.SYS
99664 93824 99968
LOGGINGDISK:[SYS0.SYSEXE]PAGEFILE3.SYS;1
2111536 1996768 2113408
LOGGINGDISK:[SYS0.SYSEXE]PAGEFILE4.SYS;1
2111536 1997424 2113408
Of the physical pages in use, 70631 pages are permanently allocated to OpenVMS.
$SHOW MEMORY/POOL/FULL
System Memory Resources on 24-MAR-2000 11:20:12.89
Nonpaged Dynamic Memory (Lists + Variable)
Current Size (bytes) 10231808 Current Size (pagelets) 19984
Initial Size 4956160 Initial Size (pagelets) 9680
Maximum Size 20840448 Maximum Size (pagelets) 40704
Free Space (bytes) 6408512 Space in Use (bytes) 3823296
Largest Variable Block 2880640 Smallest Variable Block 64
Number of Free Blocks 1529 Free Blocks LEQU 64 Bytes 365
Free Blocks on Lookasides 463 Lookaside Space (bytes) 392320
(No Bus Addressable Memory allocated)
Paged Dynamic Memory
Current Size (PAGEDYN) 2686976 Current Size (pagelets) 5248
Free Space (bytes) 1028544 Space in Use (bytes) 1658432
Largest Variable Block 1000736 Smallest Variable Block 16
Number of Free Blocks 287 Free Blocks LEQU 64 Bytes 275
$INSTALL LIST/GLOBAL
System Global Sections
. . .
DB (00000000) WRT PRM SYS
Pgltcnt/Refcnt=107424/13428
. . .
597 Global Sections Used, 343312/76336 Global Pagelets Used/Unused.
Sysgen Parameters:
-----------------
Parameters in use: Active
Parameter Name Current Default Min. Max. Unit Dynami`
PFCDEFAULT 64 64 0 2032 Pagelets D
internal value 4 4 0 127 Pages D
GBLSECTIONS 1240 250 80 65535 Sections
GBLPAGES 419635 30720 10240 -1 Pagelets D
internal value 26228 1920 640 -1 Pages D
GBLPAGFIL 3072 128 32 -1 Pages D
WSMAX 354208 4096 1024 8388608 Pagelets
internal value 22138 256 64 524288 Pages
NPAGEDYN 4956160 1048576 163840 -1 Bytes
NPAGEVIR 20840448 8388608 163840 -1 Bytes
PAGEDYN 2686976 212992 65536 -1 Bytes
WSINC 2400 2400 0 -1 Pagelets D
internal value 150 150 0 -1 Pages D
WSDEC 4000 4000 0 -1 Pagelets D
internal value 250 250 0 -1 Pages D
GROWLIM 239 63 0 -1 Pages D
BORROWLIM 239 300 0 -1 Pages D
NPAG_INTERVAL 30 30 0 -1 Seconds D
NPAG_GENTLE 85 85 0 100 Percent D
NPAG_AGGRESSIVE 50 50 0 100 Percent D
NPAG_BAP_MIN 0 0 0 -1 Bytes
NPAG_BAP_MAX 0 0 0 -1 Bytes
NPAG_BAP_MAX_PA 0 -1 0 -1 PhysAddr
NPAG_RING_SIZE 2048 2048 0 -1 Entries
FREELIM 239 32 16 -1 Pages
Thanks in advance!
Regards,
GK
The Answer is : Six times the existing 6714 pages (at 8 kilobytes per page) is roughly 300 megabytes, which is not particularly large as OpenVMS files go. Actually, 300 megabytes of data is on the smaller side as far as many common OpenVMS environments go... The GBLPAGES settings is a "blade guard", and has no optimal setting or tuning significance -- the parameter exists solely to ensure that no accidently allocates more than the specified amount... The value of WSMAX does have a potential performance impact. Those processes mapping to a 300MB global section would optimally have a working set larger than that of the section, otherwise you will tend to see pagefaulting -- most faults will probably be soft faults, but this is still overhead. If this global section is that single biggest memory-consuming application on the system, and is garantueed to have the 'right' to this memory all the time, then you should consider using RESERVED MEMORY for it -- this does have potential for a positive performance impact. (The single biggest drawback of reserved memory is that is is reserved. That is, you can not use it for anything else if the application is not there to use it. Another lesser drawback involves the need for a reboot in order to adjust the reserved memory settings.) A three megabyte virtual I/O cache on a 2 gigabyte system is rather low. If this application is heavily I/O bound, you will want to experiment with a larger VIOC setting -- somewhere closer to 3% to 10% of the total system memory. Depending on the particular file access required, also seriously consider using RMS files and RMS global buffer support -- by implementing your own file system and caching, you get to deal with the issues around memory caching and interlocking (see topic 2681), and you cannot easily extend a scheme based on global sections out into an OpenVMS Cluster. By the time you get all this working correctly and reliably, you may well have implemented everything that RMS files and global buffers already provides for you. Also please see existing discussions including topics (6960), (4487), (4051), (3791), (3635), (3365), (2486), (2637), (2181), (860), and others -- these are discussions that can be relevent to correct operations of shared memory on OpenVMS.
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