Re: [dpdk-stable] [dpdk-dev] [PATCH v2] eal/linux: do not create user mem map repeatedly when it exists

["Burakov, Anatoly" <anatoly.burakov@intel.com>]

On 23-Jul-20 3:48 PM, wangyunjian wrote:
> From: Yunjian Wang <wangyunjian@huawei.com>
> 
> Currently, we will create new user mem map entry for the same memory
> segment, but in fact it has already been added to the user mem maps.
> It's not necessary to create it twice.
> 
> To resolve the issue, add support to remove the same entry in the
> function compact_user_maps().
> 
> Fixes: 0cbce3a167f1 ("vfio: skip DMA map failure if already mapped")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Yunjian Wang <wangyunjian@huawei.com>
> ---
> v2:
> * Remove the same entry in the function compact_user_maps()
> ---
>   lib/librte_eal/linux/eal_vfio.c | 5 +++++
>   1 file changed, 5 insertions(+)
> 
> diff --git a/lib/librte_eal/linux/eal_vfio.c b/lib/librte_eal/linux/eal_vfio.c
> index abb12a354..df99307b7 100644
> --- a/lib/librte_eal/linux/eal_vfio.c
> +++ b/lib/librte_eal/linux/eal_vfio.c
> @@ -167,6 +167,10 @@ adjust_map(struct user_mem_map *src, struct user_mem_map *end,
>   static int
>   merge_map(struct user_mem_map *left, struct user_mem_map *right)
>   {
> +	/* merge the same maps into one */
> +	if (memcmp(left, right, sizeof(struct user_mem_map)) == 0)
> +		goto out;
> +

merge_map looks for adjacent maps only, but does not handle maps that 
are wholly contained within one another ("the same map" also matches 
this definition). wouldn't it be better to check for that instead of 
*just* handling identical maps?

>   	if (left->addr + left->len != right->addr)
>   		return 0;
>   	if (left->iova + left->len != right->iova)
> @@ -174,6 +178,7 @@ merge_map(struct user_mem_map *left, struct user_mem_map *right)
>   
>   	left->len += right->len;
>   
> +out:
>   	memset(right, 0, sizeof(*right));
>   
>   	return 1;
> 


-- 
Thanks,
Anatoly