Re: [libvirt] [PATCH] qemu: Drop qemuDomainMemoryLimit
On Fri, Aug 09, 2013 at 07:13:58AM -0600, Eric Blake wrote:
On 08/09/2013 06:56 AM, Michal Privoznik wrote:
> This function is to guess the correct limit for maximal memory
> usage by qemu for given domain. This can never be guessed
> correctly, not to mention all the pains and sleepless nights this
> code has caused. Once somebody discovers algorithm to solve the
> Halting Problem, we can compute the limit algorithmically. But
> till then, this code should never see the light of the release
> again.
> ---
> src/qemu/qemu_cgroup.c | 3 +--
> src/qemu/qemu_command.c | 2 +-
> src/qemu/qemu_domain.c | 49 -------------------------------------------------
> src/qemu/qemu_domain.h | 2 --
> src/qemu/qemu_hotplug.c | 2 +-
> 5 files changed, 3 insertions(+), 55 deletions(-)
ACK. Users that put an explicit limit in their XML are taking on their
own risk at guessing correctly; all other users should not be forced to
suffer from a bad guess on our part killing their domain.
If we don't understand how to calculate a default limit that works,
how are users with even less knowledge than us, suppose to calculate
an explicit level of their own ?
This limit was designed so that the hosts are not vulnerable to DOS
attack from a compromised QEMU, so removing this is arguably introducing
a security weakness in our default deployment.
I think I'd like to see some feedback / agreement from QEMU developers
that this problem really can't be solved, before we remove it.
Daniel
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