On 2/9/19 4:49 PM, Michael S. Tsirkin wrote: > On Mon, Feb 04, 2019 at 10:15:52AM -0800, Alexander Duyck wrote: >> From: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx> >> >> Add guest support for providing free memory hints to the KVM hypervisor for >> freed pages huge TLB size or larger. I am restricting the size to >> huge TLB order and larger because the hypercalls are too expensive to be >> performing one per 4K page. > Even 2M pages start to get expensive with a TB guest. Yeah, but we don't allocate and free TB's of memory at a high frequency. > Really it seems we want a virtio ring so we can pass a batch of these. > E.g. 256 entries, 2M each - that's more like it. That only makes sense for a system that's doing high-frequency, discontiguous frees of 2M pages. Right now, a 2M free/realloc cycle (THP or hugetlb) is *not* super-high frequency just because of the latency for zeroing the page. A virtio ring seems like an overblown solution to a non-existent problem.
