We've been looking at a patch that landed some months ago and have spotted some issues: https://review.openstack.org/#/c/532168 In summary, that patch is intended to make the memory check for instances memory pagesize aware. The logic it introduces looks something like this: If the instance requests a specific pagesize (#1) Check if each host cell can provide enough memory of the pagesize requested for each instance cell Otherwise If the host has hugepages (#2) Check if each host cell can provide enough memory of the smallest pagesize available on the host for each instance cell Otherwise (#3) Check if each host cell can provide enough memory for each instance cell, ignoring pagesizes This also has the side-effect of allowing instances with hugepages and instances with a NUMA topology but no hugepages to co-exist on the same host, because the latter will now be aware of hugepages and won't consume them. However, there are a couple of issues with this: 1. It breaks overcommit for instances without pagesize request running on hosts with different pagesizes. This is because we don't allow overcommit for hugepages, but case (#2) above means we are now reusing the same functions previously used for actual hugepage checks to check for regular 4k pages 2. It doesn't fix the issue when non-NUMA instances exist on the same host as NUMA instances with hugepages. The non-NUMA instances don't run through any of the code above, meaning they're still not pagesize aware We could probably fix issue (1) by modifying those hugepage functions we're using to allow overcommit via a flag that we pass for case (#2). We can mitigate issue (2) by advising operators to split hosts into aggregates for 'hw:mem_page_size' set or unset (in addition to 'hw:cpu_policy' set to dedicated or shared/unset). I need to check but I think this may be the case in some docs (sean-k-mooney said Intel used to do this. I don't know about Red Hat's docs or upstream). In addition, we did actually called that out in the original spec: https://specs.openstack.org/openstack/nova-specs/specs/juno/approved/virt-dr... However, if we're doing that for non-NUMA instances, one would have to question why the patch is necessary/acceptable for NUMA instances. For what it's worth, a longer fix would be to start tracking hugepages in a non-NUMA aware way too but that's a lot more work and doesn't fix the issue now. As such, my question is this: should be look at fixing issue (1) and documenting issue (2), or should we revert the thing wholesale until we work on a solution that could e.g. let us track hugepages via placement and resolve issue (2) too. Thoughts? Stephen