[Xen-devel] Xen 4.9 + kernel 4.13rc2 -- ballooning regression? reappearance of "Over-allocation for domain 1" errors

[PGNet Dev <pgnet.dev@xxxxxxxxx>]

I've upgraded a Xen server's

        xen-4.9.0_08-517.2.x86_64
        xen-libs-4.9.0_08-517.2.x86_64

kernel from 4.12x to 4.13x

        uname -rm
                4.13.0-rc2-2.gb545b87-default x86_64

After upgrading, I see in my Dom0-attached serial console, a steady stream of,

        ...
        (XEN) [2017-07-27 18:00:25] d1v0 Over-allocation for domain 1: 524545 > 
524544
        (XEN) [2017-07-27 18:00:58] d1v0 Over-allocation for domain 1: 524545 > 
524544
        (XEN) [2017-07-27 18:01:31] d1v0 Over-allocation for domain 1: 524545 > 
524544
        (XEN) [2017-07-27 18:02:04] d1v0 Over-allocation for domain 1: 524545 > 
524544
        (XEN) [2017-07-27 18:02:36] d1v0 Over-allocation for domain 1: 524545 > 
524544
        ...

every 32-33 seconds.

I've seen these b4, they went away afaict after mv to 4.12 kernel, and now have 
reappeared.

I didn't know 'back then' what use, or harm, these were -- and now am not clear 
if there's a new/returned problem, or just resurfaced log noise.

#irc, I was told

        Q: Any insight on what these are telling me?
        A: dom1 can't count, and is trying to grab more memory from Xen than it 
is permitted to have

This seemed possibly relevant https://patchwork.kernel.org/patch/9506769/

        "...
        I should say that this is all a gross hack, and is in desperate need of 
a proper API to make rings entirely outside of the gfn space, but this hack 
should work for now.
        ..."

I rec'd a 'simpler' suggestion, to set mem != max for dom0,

-       dom0_mem=4G,max:4G
+       dom0_mem=4016M,max:4096M

No difference.

Still getting the errors.

@ irc, suggested

        sounds like there is a new regression in the ballooning driver
        probably best email xen-devel@ and see if anyone has any ideas

Is this a real/returned problem -- or just noise?



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