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

[Ferruh Yigit <ferruh.yigit@intel.com>]

On 3/10/2016 8:37 AM, Olivier MATZ wrote:
> 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
> 
With --no-huge (since patch updates that part), it gives:
  header_size=64
  elt_size=64
  trailer_size=0
  total_obj_size=128
  private_data_size=3904

1- private_data still rounds to page size, not sure if this is a problem.
2- with MEMPOOL_DEBUG=y, trailer_size is 0, comment in code says it
should keep cookie, not sure if this is a problem.

Regards,
ferruh