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Disable KSM merging for build guests and isolate IO on dedicated threads - #66
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Host KSM merges the guest's identical pages (zeroed buffers, repeated data) and write-protects them; the next guest write then stalls on an unmerge fault serialized behind ksmd locks. Under install load this produced repeated 20-50s soft lockups on every vcpu and stretched the unattended install to ~90 minutes. Verified on the built template: with nosharepages set, the churn test went from 4-5 stalls/60s and ~6MB/s writes to zero stalls and >1GB/s.
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Host KSM merges the guest's identical pages (zeroed buffers, repeated
data) and write-protects them; the next guest write then stalls on an
unmerge fault serialized behind ksmd locks. Under install load this
produced repeated 20-50s soft lockups on every vcpu and stretched the
unattended install to ~90 minutes. Verified on the built template: with
nosharepages set, the churn test went from 4-5 stalls/60s and ~6MB/s
writes to zero stalls and >1GB/s.