On 4/15/19 3:47 PM, Martin Kletzander wrote:
On Wed, Apr 10, 2019 at 06:10:44PM +0200, Michal Privoznik wrote:
It's funny how this went unnoticed for such a long time. Long
story short, if a domain is configured with
VIR_DOMAIN_NUMATUNE_MEM_STRICT libvirt doesn't really honour
that. This is because of 7e72ac787848 after which libvirt allowed
qemu to allocate memory just anywhere and only after that it used
some magic involving cpuset.memory_migrate and cpuset.mems to
move the memory to desired NUMA nodes. This was done in order to
work around some KVM bug where KVM would fail if there wasn't a
DMA zone available on the NUMA node. Well, while the work around
might stopped libvirt tickling the KVM bug it also caused a bug
on libvirt side: if there is not enough memory on configured NUMA
node(s) then any attempt to start a domain must fail. Because of
the way we play with guest memory domains can start just happily.
The solution is to move the child we've just forked into emulator
cgroup, set up cpuset.mems and exec() qemu only after that.
So you are saying this was a bug in KVM? Is it fixed now? I am not
against
this patch, I hated that I had to do the workaround, but I just want to
be sure
we won't start hitting that again.
Yes, that's what I'm saying. Looks like the KVM bug is fixed now because
with a Fedora 29 on a NUMA machine I can start domains just fine.
Signed-off-by: Michal Privoznik <mprivozn@xxxxxxxxxx>
---
src/qemu/qemu_process.c | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)
diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
index 47d8ca2ff1..076ec18e21 100644
--- a/src/qemu/qemu_process.c
+++ b/src/qemu/qemu_process.c
@@ -6653,6 +6653,14 @@ qemuProcessLaunch(virConnectPtr conn,
if (qemuProcessInitCpuAffinity(vm) < 0)
goto cleanup;
+ VIR_DEBUG("Setting emulator tuning/settings");
+ if (qemuProcessSetupEmulator(vm) < 0)
+ goto cleanup;
+
+ VIR_DEBUG("Setting up post-init cgroup restrictions");
This is not post-init any more, but more importantly,
+ if (qemuSetupCpusetMems(vm) < 0)
This function does a subset of what qemuProcessSetupEmulator() called right
before, does, so I see no reason for it being called here, or to keep
existing
in the codebase for that matter.
Ah, good point. I'll send v3.
Michal
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