Pkg xen devel - Feb 2019 - Bug#880554: Bug#880554: #880554: max grant frames problem

Hi,

Our Buster TODO [1] has a TODO item for me about adding a paragraph in
the "Known Issues" section of the Debian README / NEWS / or wherever
it
will go about the grant frames issue.

It would be very nice to have some WARN_ONCE code in the linux kernel
exactly at the place where this issue happens, but nobody has been
adding that yet, so for now, if this happens, domUs will just still hang
without meaningful stuff in dmesg.

I also have a suspicion that this issue will be showing up less when
using Xen 4.11+ and Linux 4.19+ in dom0 and domU (so, yay, upgrade all
the things!). Newer Linux kernel versions have patches that also
actually release frame stuff when it's no longer actually in use, which
might end the 'only-going-up' behaviour of the number we see.

Anyway, I'm planning to add some "known issue" documentation about
this
to the Xen 4.11 packaging, together with a clear short description of
what to change where in what configuration (because in Xen 4.11+ it's
different than in 4.4 or 4.8 again), and then mark this bts as closed
while that upload happens.

Digging around in kernel code to find out where this happens and adding
this WARN_ONCE is still a nice kernel coding exercise, but I don't want
this bts to track if that ends up on top of my TODO list or not.

Hans

[1] https://salsa.debian.org/xen-team/debian-xen/issues/24