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New: memory ballooning doesn't take on boot since approx kernel 4.5.3

Bug 190211 [email protected] 1 participant 3 messages Dec 13, 2016 – Dec 14, 2016 KVM

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https://bugzilla.kernel.org/show_bug.cgi?id=190211

            Bug ID: 190211
           Summary: memory ballooning doesn't take on boot since approx
                    kernel 4.5.3
           Product: Virtualization
           Version: unspecified
    Kernel Version: 4.9, 4.8.14, 4.8.1, 4.7.2, 4.6.2
          Hardware: All
                OS: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: kvm
          Assignee: [email protected]
          Reporter: [email protected]
        Regression: No

Just noticed that on restart or bootup memory ballooning stopped working. The guest boots with the maximum allowed memory rather than the "current" setting in libvirt.

If I request a memory shrink after boot, the balloon works and memory available shrinks as requested.

I went through the following guest kernels: 4.9, 4.8.14, 4.8.1, 4.7.2, 4.6.2, 4.5.3 (worked), 4.4.4 (worked). These were custom compiles. Debian official kernels for 4.8.0 and 4.7.0 also failed.

I used libvirt 2.5.0, 2.4.0 and 1.2.20

Qemu versions: 2.5 and 2.7

Debian stretch for the guest, wheezy and stretch for the host.

Host kernels 4.3.3, 4.8.6 and 4.8.14

The fact that dropping kernel versions made it work once I hit 4.5.3 makes me think there's an issue kernel-side.

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[Bug 190211] memory ballooning doesn't take on boot since approx kernel 4.5.3

In reply to [email protected]

https://bugzilla.kernel.org/show_bug.cgi?id=190211

--- Comment #1 from [email protected] ---
I've done a bit more poking around with kernel 4.9.

It appears that enabling NUMA on the guest kernel but /not/ using it (ie I've not configured numa use via libvirt in qemu) is enough to fix this. The kernel gets the lowered memory on reboot and on boot.

Is this how it is meant to function or is this still a bug?

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