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I ran a KVM VM on my CentOS host and found that after performing a HDD-intensive operation, it used all of the host's memory I assigned to it. However, free on the guest suggests that the memory's only cached. Does the host also cache the hard disk blocks the guest used? If so, can I somehow disable HDD buffering in the guest, assuming that the VM host is going to perform it anyway?

  • you usually can't trust anything that a guest tells you about itself. – Jesse K Apr 1 '16 at 15:41
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    You can choose KVM/qemu's i/o and caching methods to tune performance. See, for example, the serverfault question serverfault.com/questions/425607/… – Mark Plotnick Apr 1 '16 at 17:29

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