Red Hat Bugzilla – Bug 1308744
[RFE] PAPR Hash Page Table (HPT) resizing (RHEV) [blocked on platform bugs]
Last modified: 2017-05-11 09:57:21 EDT
RHEV should determine if the guest supports HPT resizing, then increase the default max size of memory. +++ This bug was initially created as a clone of Bug #1308743 +++ In case libvirt requires changes to support HPT resizing. If no changes required, set this BZ to TestOnly. +++ This bug was initially created as a clone of Bug #1305398 +++ Description of problem: Allow the hash page table (HPT) of PAPR guests to be resized at runtime. This is important for practical memory hotplug. Without this the HPT needs to be sized for the guest's maximum possible memory - since RHEV wants to set that to 4T, this can result in a much bigger than necessary HPT which wastes host resources and can cause allocation failures. With HV KVM the HPT is unswappable, contiguous host memory. This BZ covers the qemu parts of this including TCG and PR KVM implementation of the necessary hypercalls, feature negotation with the guest and enabling the necessary KVM host pieces. --- Additional comment from David Gibson on 2016-02-07 19:52:00 EST --- An RFC has been posted upstream: https://lists.gnu.org/archive/html/qemu-devel/2016-01/msg05852.html
*** Bug 1308746 has been marked as a duplicate of this bug. ***
The resize-hpt=required machine option in qemu might be useful for RHEV to determine if the guest supports HPT resizing. With that option qemu will refuse to boot a guest which does not support it (exiting with an error during boot). So, RHEV could boot with that option, then if the boot fails adjust the max memory size down and restart with without the option to run the non-HPT-resize aware guest. Obviously RHEV might then want to cache the value, and/or pre-populate it when it knows the distro / version of the guest.