Re: [dpdk-dev] [PATCH, v2] mempool: avoid memory waste with large pagesize

[Olivier MATZ <olivier.matz@6wind.com>]

Hello,

On 03/09/2016 10:12 PM, Stephen Hemminger wrote:
> If page size is large (like 64K on ARM) and object size is small
> then don't waste lots of memory by rounding up to page size.
> Instead, round up so that 1 or more objects all fit in a page.
> 
> This preserves the requirement that an object must not a page
> or virt2phys would break, and makes sure 62K is not wasted per mbuf.
> 
> Also, fix invalid use of printf (versus log) for error reporting.
> 
> Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
> ---
> v2 - fix trailer_size calculation, and replace printf with log
> 
>  lib/librte_mempool/rte_mempool.c | 23 ++++++++++++++---------
>  1 file changed, 14 insertions(+), 9 deletions(-)
> 
> diff --git a/lib/librte_mempool/rte_mempool.c b/lib/librte_mempool/rte_mempool.c
> index f8781e1..ff08a1a 100644
> --- a/lib/librte_mempool/rte_mempool.c
> +++ b/lib/librte_mempool/rte_mempool.c
> @@ -300,18 +300,23 @@ rte_mempool_calc_obj_size(uint32_t elt_size, uint32_t flags,
>  	if (! rte_eal_has_hugepages()) {
>  		/*
>  		 * compute trailer size so that pool elements fit exactly in
> -		 * a standard page
> +		 * a standard page. If elements are smaller than a page
> +		 * then allow multiple elements per page
>  		 */
> -		int page_size = getpagesize();
> -		int new_size = page_size - sz->header_size - sz->elt_size;
> -		if (new_size < 0 || (unsigned int)new_size < sz->trailer_size) {
> -			printf("When hugepages are disabled, pool objects "
> -			       "can't exceed PAGE_SIZE: %d + %d + %d > %d\n",
> -			       sz->header_size, sz->elt_size, sz->trailer_size,
> -			       page_size);
> +		unsigned new_size, orig_size, page_size;
> +
> +		page_size = getpagesize();
> +		orig_size = sz->header_size + sz->elt_size;
> +		new_size = rte_align32pow2(orig_size);
> +		if (new_size > page_size) {
> +			RTE_LOG(ERR, MEMPOOL,
> +				"When hugepages are disabled, pool objects "
> +				"can't exceed PAGE_SIZE: %u + %u + %u > %u\n",
> +				sz->header_size, sz->elt_size, sz->trailer_size,
> +				page_size);
>  			return 0;
>  		}
> -		sz->trailer_size = new_size;
> +		sz->trailer_size = new_size - orig_size;
>  	}
>  
>  	/* this is the size of an object, including header and trailer */
> 

It still does not work. When CONFIG_RTE_LIBRTE_MEMPOOL_DEBUG=y:

mp = rte_mempool_create("test", 128,
	64, 0, 0, NULL, NULL, NULL, NULL, SOCKET_ID_ANY, 0);
rte_mempool_dump(stdout, mp);

  populated_size=128
  header_size=64
  elt_size=64
  trailer_size=64
  total_obj_size=192


Regards,
Olivier