Hi, KVM developer: A correction to my previous post. I found that NOT all page fault in the guest could cause kvm_page_fault event in the hypervisor. For example, my array access microbencharmk touches 1024 pages (as an integer array). In the guest VM, I can trace 1024 page fault events. However, in the hypervisor host, I can only trace about 50 kvm_page_fault events. Could anyone explain why the those page faults in the guest are not exposed to the hypervisor? Thanks. The KVM module has disabled ept and host kernel is 3.2.14. - Hui On Sun, Oct 19, 2014 at 2:19 AM, Steven <wangwangkang@xxxxxxxxx> wrote: > Hi, Paolo, > As you said the memory pages may have already be touched by the guest, > although it still cause page fault from the VM. > > So my question is will KVM pre-allocate some physical pages (by > calling get_user_page_fast) to the guest? > If so, when a user-space program in the guest requests for pages, how > does KVM decide which pre-allocated physical pages are to be > allocated? > > Because in this microbenchmark, for each virtual page fault in the > guest, I can trace there is a corresponding kvm_page_fault event, but > not mm_alloc_page event (which is the function of allocating page by > the buddy allocator). > > Thanks in advance. > > - Steven > > On Wed, Sep 17, 2014 at 3:22 PM, Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote: >> Il 17/09/2014 19:19, Steven ha scritto: >>> I think get_user_pages or get_user_pages finally will call >>> mm_page_alloc, right?. >>> However, for the small size array, I observer many >>> kmem_cache_alloc_node and kmalloc_node physical page allocation, but >>> very few mm_page_alloc trace. So will the host kernel assign the >>> memory to the VM from slab allocator? Thanks. >> >> I don't think so. Likely the memory had already been touched by the guest. >> >> Paolo -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
