Wikipedia says the “Principle of least astonishment” is that systems
(software) should behave in a manner consistent with how users of that
component are likely to expect it to behave, i.e., users should not be
astonished at the way it behaves.
I’m trying to apply this principle to memory operations on z/VM and Linux
in zoom line commands.
I believe Linux running on z/VM has 3 types of memory, all of which can be
different:
1) That defined in the user directory
2) That defined in CP for a running system
3) That defined in and used by a running Linux
While they can all be different, it's probably best to keep all three in
sync so you can say "That Linux system has <amount> of memory."
Then to complicate matters, there are maximum and 'standby' amounts, the
latter of which is necessary if memory is to be added dynamically to
running Linux systems. The initial, maximum and standby can also get out of
sync in the user directory and again it's probably best that they don't
First some terminology.
-) 'soft reboot' - Linux 'init 6' - does not log off/on virtual machine
-) 'hard reboot' - Linux halt, logoff, logon, boot
So, for some hopefully intuitively named line commands, is this how you'd
expect them to behave?
zaddmemory linux1,linux2 1g
Add 1g to user directory initial, CP and Linux memory on nodes linux1 and
linux2.
If 'COMMAND DEF STOR <init> STANDBY <stby>' is found, add to <init>,
subtract from <stby>
zrmmemory linux1,linux2 1g
Remove 1g from user directory initial, CP and Linux memory on nodes
linux1 and linux2.
If 'COMMAND DEF STOR <init> STANDBY <stby>' is found, subtract from
<init>, add to <stby>
zaddmemory --initial linux1 1g
Add 1g to user directory initial only => take effect after hard reboot.
If 'COMMAND DEF STOR <init> STANDBY <stby>' is found, add to <init>,
subtract from <stby>
zaddmemory --temp linux1 1g
Add 1g to running linux1 only => will be gone after hard or soft reboot,
no change to user directory.
zsetmemory --maximum linux1 8g
Set linux1 maximum meomory to 8G in user directory.
If 'COMMAND DEF STOR <init> STANDBY <stby>' is found, set <stby> to <max>
- <init>.
zsetmemory --standby linux1 7G
Set linux1 standby memory only to 7G.
Let me add some feedback as I think about the last example - setting
STANDBY only would by definition get settings out of sync, so maybe it
would be astonishing to allow such an option.
Thanks for any feedback.
-Mike MacIsaac
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