RE: [Xen-devel] [PATCH] linux/balloon: don't allow ballooningdowna domain below a reasonable limit

["Dan Magenheimer" <dan.magenheimer@xxxxxxxxxx>]

> From: Keir Fraser [mailto:keir.fraser@xxxxxxxxxxxxx]
> Okay, I will comment when I see it. I'm not sure what design you are working
> on: perhaps extract memory stats from the guest via xenbus and implement
> ballooning policy in dom0? That is what I would prefer to see. The Novell
> ballooning-limit checks were only added as a safety backstop in the guest
> itself. Apart from tweaking it to make it less conservative where we are
> confident that is safe, any more complicated policy, and of course and
> cross-domain global optimisation, doesn't belong in the 
> individual guests.

(cc's removed due to topic drift)

I was planning on providing both Model C and Model D (see below),
but let me know if you will only accept Model C (or even Model B)
and I will adjust accordingly. 

===============
MODEL A (current):

Domain 0 sez: "Hey guest A, I have no clue how much memory you have
(though you may or may not have obeyed a previous request) or how much
you need, but change your memory usage to 150MB"
Guest A (silently): "(Silly domain 0 wants me to reduce my memory
usage to 150MB but my minimum is 160MB.  Well, I guess I'll do
my best.)"
===============
MODEL B (guest provides info when prodded):

Domain 0 sez: "Hey guest A, tell me how much memory you have and how
much you need"
Guest A sez: "I have 198MB but I really only need 129MB"
Domain 0 sez: "Guest A, reduce your memory usage to 129MB"
Guest A (silently): "(My min is 150MB but I'll do my best)"
Domain 0 sez: "Hey guest A, tell me how much memory you have and how
much you need"
Guest A sez: "I have 150MB but I really only need 129MB"
[etc]
===============
MODEL C (guest provides info regularly):

Guest A sez: "I have 198 MB, I really only need 180MB, and my
minimum is 150MB.  I'll provide another update in a second."
[one second later]
Guest A sez: "I have 198 MB, I really only need 129MB, and my
minimum is 150MB.  I'll provide another update in a second."
Domain 0 sez: "Guest A, reduce your memory to 150MB"
Guest A (silently): "(ballooning down now to 150MB)"
[one second later]
Guest A sez: "I have 150MB, I really need 250MB and my minimum
is 150MB. I'll provide another update in a second."
Domain 0 sez: "Guest A, increase your memory to 250MB"
===============
MODEL D (autoballooning):

Domain 0 sez: "Hey Guest A, do the right thing with your memory"
Guest A sez: "I have 198MB, I really only need 129MB, and my
minimum is 150MB"
Guest A (silently): "(ballooning down now to 150MB)"
[one second later]
Guest A sez: "I have 150MB, I really need 250MB, and my
minimum is 150MB"
Guest A (silently): "(ballooning up now to 250MB... oops looks
like I can't get that much but I'll take what I can get)"
[one second later]
Guest A sez: "I have 200MB, I really need 300MB, and my
minimum is 150MB"
Guest A (silently): "(ballooning up now to 250MB... oops looks
like I can't get any more... time to start swapping)"


===================================
Thanks... for the memory
I really could use more / My throughput's on the floor
The balloon is flat / My swap disk's fat / I've O-O-M's in store
Overcommitted we are
(with apologies to the late great Bob Hope)


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