Re: [dpdk-dev] [PATCH 2/4] mempool: detect physical contiguous object in pool

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

On Wed, 21 Jun 2017 17:32:46 +0000, Santosh Shukla <santosh.shukla@caviumnetworks.com> wrote:
> HW mempool blocks may need physical contiguous obj in a pool.

This should be clarified: the memory area containing all the
objects must be physically contiguous, right?

> Introducing MEMPOOL_F_POOL_CONTIG flag for such use-case.  The flag
> useful to detect whether all buffer fits within a hugepage or not. If
> not then return -ENOSPC. This way, we make sure that all object within a
> pool is contiguous.
> 
> Signed-off-by: Santosh Shukla <santosh.shukla@caviumnetworks.com>
> Signed-off-by: Jerin Jacob <jerin.jacob@caviumnetworks.com>
> ---
>  lib/librte_mempool/rte_mempool.c | 8 ++++++++
>  lib/librte_mempool/rte_mempool.h | 1 +
>  2 files changed, 9 insertions(+)
> 
> diff --git a/lib/librte_mempool/rte_mempool.c b/lib/librte_mempool/rte_mempool.c
> index 045baef45..7dec2f51d 100644
> --- a/lib/librte_mempool/rte_mempool.c
> +++ b/lib/librte_mempool/rte_mempool.c
> @@ -368,6 +368,14 @@ rte_mempool_populate_phys(struct rte_mempool *mp, char *vaddr,
>  
>  	total_elt_sz = mp->header_size + mp->elt_size + mp->trailer_size;
>  
> +	/* Detect nb_mbuf fit in hugepage */
> +	if (mp->flags & MEMPOOL_F_POOL_CONTIG) {
> +		if (len < total_elt_sz * mp->size) {
> +			RTE_LOG(ERR, MEMPOOL, "nb_mbufs not fitting in one hugepage,..exit\n");
> +			return -ENOSPC;
> +		}
> +	}
> +

We should not reference mbuf, we are in mempool code, dealing with
any kind of object.

Also, len is not necessarily the size of a hugepage, but the size of the
physical area passed to te_mempool_populate_phys().

>  	memhdr = rte_zmalloc("MEMPOOL_MEMHDR", sizeof(*memhdr), 0);
>  	if (memhdr == NULL)
>  		return -ENOMEM;
> diff --git a/lib/librte_mempool/rte_mempool.h b/lib/librte_mempool/rte_mempool.h
> index c3cdc77e4..fd8722e69 100644
> --- a/lib/librte_mempool/rte_mempool.h
> +++ b/lib/librte_mempool/rte_mempool.h
> @@ -266,6 +266,7 @@ struct rte_mempool {
>  #define MEMPOOL_F_SC_GET         0x0008 /**< Default get is "single-consumer".*/
>  #define MEMPOOL_F_POOL_CREATED   0x0010 /**< Internal: pool is created. */
>  #define MEMPOOL_F_NO_PHYS_CONTIG 0x0020 /**< Don't need physically contiguous objs. */
> +#define MEMPOOL_F_POOL_CONTIG    0x0040 /**< Detect physcially contiguous objs */

We must highlight here that it's a capability flag.
Following my other comments on the first patch, this define should be
renamed in something else. I suggest:

#define RTE_MEMPOOL_CAPA_PHYS_CONTIG 0x0001

The description should be longer and more accurate.

I'm also a bit puzzled because this is more a limitation than a
capability.

>  
>  /**
>   * @internal When debug is enabled, store some statistics.