[Qemu-devel] Re: [PATCH] add MADV_DONTFORK to guest physical memory

[Michael S. Tsirkin]

On Wed, Sep 15, 2010 at 07:08:24PM +0200, Andrea Arcangeli wrote:
> From: Andrea Arcangeli <address@hidden>
> 
> All allocated guest physical memory shall be marked MADV_DONTFORK, otherwise
> fork will fail because of accounting issues preventing migration or netdev_add
> when the guest allocated more than half of host physical memory.
> 
> Signed-off-by: Andrea Arcangeli <address@hidden>
> ---
> 
> diff --git a/exec.c b/exec.c
> index 380dab5..e2bdf19 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -2861,6 +2861,9 @@ ram_addr_t qemu_ram_alloc_from_ptr(DeviceState *dev, 
> const char *name,
>  #ifdef MADV_MERGEABLE
>              madvise(new_block->host, size, MADV_MERGEABLE);
>  #endif
> +#ifdef MADV_DONTFORK
> +            madvise(new_block->host, size, MADV_DONTFORK);
> +#endif
>          }
>      }

Is this always a number of full host pages? If not, we'd get trouble
when trying to call helpers.

-- 
MST