On 27/05/20 16:26, Igor Mammedov wrote: > On Wed, 27 May 2020 15:06:28 +0200 > Paolo Bonzini <pbonz...@redhat.com> wrote: > >> On 27/05/20 14:25, Igor Mammedov wrote: >>>> (2) we loose a gigabyte page. >>> I'm not sure waht exactly we loose in this case. >>> Lets assume we allocating guest 5G of continuous RAM using 1G >>> huge pages, >>> in this case I'd think that on host side MMIO overlay won't >>> affect RAM blob >>> on guest side pagetables will be fragmented due to MMIO holes, >>> but guest still >>> could use huge pages smaller ones in fragmented area and 1G where >>> there is no fragmentation. >> >> Access to the 3G-4G area would not be able to use 1G EPT pages. > Could it use 2Mb pages instead of 1Gb?
Yes, probably a mix of 2 MiB pages and 4 KiB pages around the memslot splits. > Do we really care about 1 gigabyte huge page in microvm intended usecase? > (fast starting VMs for microservices like FaaS, which unlikely would use much > memory to begin with) I honestly don't think it's measurable, but at least in theory we care because such workloads could have more TLB misses (relative to the execution time) than long-lasting VMs. Paolo
