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Committed 27 Jan 2026 02:16PM UTC coverage: 80.459%. Remained the same

Job # 21400617348.1

Build Type

push

github

Committed by

web-flow

Commit Message

CA-423172: Xen uses ~294 pages/vCPU, not 256 (#6854)

Measured the actual increase in host memory usage when increasing the
number of vCPUs on a VM from 1 to 64:

```
delta vcpu,delta memory_overhead_pages,coeff
1,264,264
3,724,241.333
7,1848,264
15,3960,264
31,8186,264.065
63,16635,264.048
```

Ran the test on both an AMD and Intel host and got similar results.

Currently XAPI uses 256*vcpu, which is an underestimate.

This can lead to internal errors raised by xenguest, or
NOT_ENOUGH_FREE_MEMORY errors raised by xenopsd, after
`assert_can_boot_here` has already replied yes, even when booting VMs
sequentially.
It could also lead XAPI to choose the wrong host to evacuate a VM too,
which could lead to RPU migration failures.

This is a pre-existing bug, affecting both the versions of Xen in XS8
and XS9.

PR to feature branch because this will need testing together with all
the other NUMA changes, it may expose latent bugs elsewhere.

The new testcase will get its own PR because it is quite large.

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