Il 06/08/2013 18:55, Andreas Färber ha scritto: > Am 25.07.2013 12:32, schrieb Andrea Arcangeli: >> On Thu, Jul 25, 2013 at 11:16:44AM +0100, Peter Maydell wrote: >>> On 25 July 2013 11:11, Andrea Arcangeli <aarca...@redhat.com> wrote: >>>> diff --git a/exec.c b/exec.c >>>> index c99a883..d3bb58d 100644 >>>> --- a/exec.c >>>> +++ b/exec.c >>>> @@ -1162,6 +1162,7 @@ ram_addr_t qemu_ram_alloc_from_ptr(ram_addr_t size, >>>> void *host, >>>> >>>> qemu_ram_setup_dump(new_block->host, size); >>>> qemu_madvise(new_block->host, size, QEMU_MADV_HUGEPAGE); >>>> + qemu_madvise(new_block->host, size, QEMU_MADV_DONTFORK); >>>> >>>> if (kvm_enabled()) >>>> kvm_setup_guest_memory(new_block->host, size); >>>> >>> >>> kvm_setup_guest_memory() already calls >>> qemu_madvise(start, size, QEMU_MADV_DONTFORK) >>> so why do we need to do it here as well? >> >> That only runs if kvm is enabled and mmu is not sync. But we need it >> in the common case too, to prevent -ENOMEM (if MADV_DONTFORK is >> available in the host OS, otherwise well we'll just do best effort and >> skip). See commit message for more details. > > So if we add the DONTFORK unconditionally here, why not drop it in said > kvm_setup_guest_memory()? That would make the patch more > self-documenting while at it.
This is mentioned in the commit message: "In the common case we can ignore the error if MADV_DONTFORK is not available. Leave a second invocation that errors out in the KVM path if MMU notifiers are missing and KVM is enabled, to abort in such case". Paolo
