[dpdk-dev] [PATCH] mempool: avoid memory waste with large pagesize
Olivier MATZ
olivier.matz at 6wind.com
Wed Mar 9 18:49:45 CET 2016
On 03/09/2016 03:29 AM, 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.
You should specify that it only affects runs with "--no-huge".
> --- a/lib/librte_mempool/rte_mempool.c
> +++ b/lib/librte_mempool/rte_mempool.c
> @@ -300,18 +300,24 @@ 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) {
> + unsigned page_size = getpagesize();
> + uint32_t orig_size, new_size;
> +
> + orig_size = sz->header_size + sz->elt_size;
> + new_size = rte_align32pow2(orig_size);
> + if (new_size > page_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);
> return 0;
> }
> - sz->trailer_size = new_size;
> +
> + sz->trailer_size = (new_size - orig_size)
> + / (page_size / new_size);
> }
Looks it does not work, did I miss something?
Examples:
# start with --no-huge
mp = rte_mempool_create("test", 128,
35, 0, 0, NULL, NULL, NULL, NULL, SOCKET_ID_ANY, 0);
rte_mempool_dump(stdout, mp);
shows:
header_size=64
elt_size=40
trailer_size=0
total_obj_size=104 <<<<< should be 128?
# start with --no-huge
mp = rte_mempool_create("test", 128,
191, 0, 0, NULL, NULL, NULL, NULL, SOCKET_ID_ANY,
MEMPOOL_F_NO_CACHE_ALIGN);
rte_mempool_dump(stdout, mp);
shows:
header_size=8
elt_size=192
trailer_size=3
total_obj_size=203 <<<<< should be 256?
The RFC I've just submitted also aims to fix this issue
(but differently).
Regards,
Olivier
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