What were you trying to do that didn't work?

Enable balloon polling and then enlarge or envict guest memory via balloon device, after memory is stable checking the guest memory size. Some times, the memory couldn't get to the expected size, the gap is almost 380-648M.

Please provide the package NVR for which the bug is seen:

virtio-win-prewhql-0.1-293

How reproducible is this bug?:

It can't be reproduced consistenly.  It sometimes shows up in acceptance tests.

Steps to reproduce

1. Enable balloon polling and set the interval to 2s. 

 {"execute": "qom-set", "arguments":

 , "id": "fg4J7YWH"}

2. get guest memory inside guest and get the memory size via qemu monitor

2025-10-20 10:18:02: 192.168.122.46Available Physical Memory: 11,770 MB

2025-10-20 10:17:58,176 avocado.virttest.qemu_monitor qemu_monitor     L1993 DEBUG| (monitor avocado-vt-vm1.qmp1)    actual: 13917749248

3. change vm memory to 5891

2025-10-20 10:18:02,798 avocado.virttest.qemu_monitor qemu_monitor L2074 DEBUG| Send command: {"execute": "balloon", "arguments":

, "id": "xiPBDEuN"}

4. When the memory is stable, check the memory in guest and qemu monitor

2025-10-20 10:18:13: 192.168.122.46Virtual Memory: Available: 7,784 MB

2025-10-20 10:18:08,815 avocado.virttest.qemu_monitor qemu_monitor     L1993 DEBUG| (monitor avocado-vt-vm1.qmp1)    actual: 6177161216

[stdlog] 2025-10-20 10:18:13,400 avocado.test balloon_check L0459 ERROR| Memory size mismatch after evict memory:

[stdlog] 2025-10-20 10:18:13,401 avocado.test balloon_check L0465 ERROR| Wanted to be changed: -7382.0 [stdlog] Changed in monitor: -7382.0

[stdlog] Changed in guest: -8030

The gap is 648M

Expected results

No big gap after balloon function

Note:

Checking the previous test runs, win11, win2016, win2022 have all encountered this issue before.

The automation logs:

http://virtqetools.lab.eng.pek2.redhat.com/autotest_static_job_log/11916394/test-results/104-Host_RHEL.m9.u4.ovmf.qcow2.virtio_blk.up.virtio_net.Guest.Win2022.x86_64.io-github-autotest-qemu.balloon_service.small_polling_interval.q35/

http://10.73.156.41/pub/logs/virtio-win-1.9.49-0.el9_6-win1032-win2016/test-results/198-Host_RHEL.m9.u6.qcow2.virtio_blk.up.virtio_net.Guest.Win2016.x86_64.io-github-autotest-qemu.balloon_servic e.small_polling_interval.q35/ 

http://virtqetools.lab.eng.pek2.redhat.com/autotest_static_job_log/11760609/test-results/33-Host_RHEL.m10.u1.ovmf.qcow2.virtio_scsi.up.virtio_net.Guest.WinNext.x86_64.io-github-autotest-qemu.balloon_service.small_polling_interval.q35/