On Thu, Jul 25, 2013 at 12:11:15PM +0200, 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 <aarca...@redhat.com>
Applied to uq/master, thanks.
> ---
> 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);
--
Gleb.
