| 2019-01-15 16:48:41 |
Stephen Finucane |
description |
libvirt < 4.3.0 had an issue whereby assigning more than 4 GB of huge pages would result in an incorrect value for the number of hugepages. This was tracked and fixed via rhbz#1569678 and the fixes appear to have been backported to the libvirt versions for RHEL 7.4+. However, this is still an issue with the versions of libvirt available on Ubuntu 16.04, 18.04 and who knows what else. We should either alert the user that the bug exists or, better again, work around the issue using the rest of the (correct) values for different page sizes.
# Incorrect value (Ubuntu 16.04, libvirt 4.0.0)
$ virsh capabilities | xmllint --xpath /capabilities/host/topology/cells/cell[1] -
<cell id="0">
<memory unit="KiB">16298528</memory>
<pages unit="KiB" size="4">3075208</pages>
<pages unit="KiB" size="2048">4000</pages>
<pages unit="KiB" size="1048576">0</pages>
...
</cell>
(3075208 * 4) + (4000 * 2048) != 16298528
# Correct values (Fedora ??, libvirt 4.10)
$ virsh capabilities | xmllint --xpath /capabilities/host/topology/cells/cell[1] -
<cell id='0'>
<memory unit='KiB'>32359908</memory>
<pages unit='KiB' size='4'>8038777</pages>
<pages unit='KiB' size='2048'>100</pages>
<pages unit='KiB' size='1048576'>0</pages>
...
</cell>
(8038777 * 4) + (100 * 2048) == 32359908
[1] https://bugzilla.redhat.com/show_bug.cgi?id=1569678 |
libvirt < 4.3.0 had an issue whereby assigning more than 4 GB of huge pages would result in an incorrect value for the number of 4k (small) pages. This was tracked and fixed via rhbz#1569678 and the fixes appear to have been backported to the libvirt versions for RHEL 7.4+. However, this is still an issue with the versions of libvirt available on Ubuntu 16.04, 18.04 and who knows what else. We should either alert the user that the bug exists or, better again, work around the issue using the rest of the (correct) values for different page sizes.
# Incorrect value (Ubuntu 16.04, libvirt 4.0.0)
$ virsh capabilities | xmllint --xpath /capabilities/host/topology/cells/cell[1] -
<cell id="0">
<memory unit="KiB">16298528</memory>
<pages unit="KiB" size="4">3075208</pages>
<pages unit="KiB" size="2048">4000</pages>
<pages unit="KiB" size="1048576">0</pages>
...
</cell>
(3075208 * 4) + (4000 * 2048) != 16298528
# Correct values (Fedora ??, libvirt 4.10)
$ virsh capabilities | xmllint --xpath /capabilities/host/topology/cells/cell[1] -
<cell id='0'>
<memory unit='KiB'>32359908</memory>
<pages unit='KiB' size='4'>8038777</pages>
<pages unit='KiB' size='2048'>100</pages>
<pages unit='KiB' size='1048576'>0</pages>
...
</cell>
(8038777 * 4) + (100 * 2048) == 32359908
[1] https://bugzilla.redhat.com/show_bug.cgi?id=1569678 |
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