Re: [PATCH 4/4] vhost: avoid populate guest memory

[Maxime Coquelin <maxime.coquelin@redhat.com>]

Hi Jianfeng,

On 02/14/2018 05:01 AM, Jianfeng Tan wrote:
> It's not necessary to polulate guest memory from vhost side.
> 
> Cc: maxime.coquelin@redhat.com
> Cc: yliu@fridaylinux.org
> 
> Signed-off-by: Jianfeng Tan <jianfeng.tan@intel.com>
> ---
>   lib/librte_vhost/vhost_user.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/librte_vhost/vhost_user.c b/lib/librte_vhost/vhost_user.c
> index 90ed211..9bd0391 100644
> --- a/lib/librte_vhost/vhost_user.c
> +++ b/lib/librte_vhost/vhost_user.c
> @@ -644,6 +644,7 @@ vhost_user_set_mem_table(struct virtio_net *dev, struct VhostUserMsg *pmsg)
>   	uint64_t mmap_offset;
>   	uint64_t alignment;
>   	uint32_t i;
> +	int populate;
>   	int fd;
>   
>   	if (dev->mem && !vhost_memory_changed(&memory, dev->mem)) {
> @@ -714,8 +715,9 @@ vhost_user_set_mem_table(struct virtio_net *dev, struct VhostUserMsg *pmsg)
>   		}
>   		mmap_size = RTE_ALIGN_CEIL(mmap_size, alignment);
>   
> +		populate = (dev->dequeue_zero_copy) ? MAP_POPULATE : 0;
>   		mmap_addr = mmap(NULL, mmap_size, PROT_READ | PROT_WRITE,
> -				 MAP_SHARED | MAP_POPULATE, fd, 0);
> +				 MAP_SHARED | populate, fd, 0);
>   
>   		if (mmap_addr == MAP_FAILED) {
>   			RTE_LOG(ERR, VHOST_CONFIG,
> 

Wouldn't not populating all the guest memory have a bad impact on 0%
acceptable loss use-cases?

Thanks,
Maxime