[Qemu-devel] PING for-1.6 Re: [PATCH] KVM: always use MADV_DONTFORK

[Paolo Bonzini <pbonzini@redhat.com>]

On 07/25/2013 12:11 PM, Andrea Arcangeli wrote:
> MADV_DONTFORK prevents fork to fail with -ENOMEM if the default
> overcommit heuristics decides there's too much anonymous virtual
> memory allocated. If the KVM secondary MMU is synchronized with MMU
> notifiers or not, doesn't make a difference in that regard.
>
> Secondly it's always more efficient to avoid copying the guest
> physical address space in the fork child (so we avoid to mark all the
> guest memory readonly in the parent and so we skip the establishment
> and teardown of lots of pagetables in the child).
>
> 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.
>
> Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
> ---
>   exec.c | 1 +
>   1 file changed, 1 insertion(+)
>
> 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);
>
>

PING.

Benoit reported this on IRC, too.

Paolo