mempool name size incorrect?

[Andrew Rybchenko]

On 3/10/26 5:10 PM, Morten Brørup wrote:
> Isn't the RTE_MEMPOOL_NAMESIZE too short?
> 
> Looking at the names sizes:
> 
> RTE_MEMZONE_NAMESIZE = 32,
> RTE_RING_NAMESIZE = RTE_MEMZONE_NAMESIZE - (sizeof("RG_")=4) + 1 = 29,
> RTE_MEMPOOL_NAMESIZE = RTE_RING_NAMESIZE - (sizeof("MP_")=4) + 1 = 26
> 
> Referring to [1], I think it should be fixed as:
> - #define RTE_MEMPOOL_NAMESIZE (RTE_RING_NAMESIZE - \
> 			      sizeof(RTE_MEMPOOL_MZ_PREFIX) + 1)
> + #define RTE_MEMPOOL_NAMESIZE (RTE_MEMZONE_NAMESIZE - \
> 			      sizeof(RTE_MEMPOOL_MZ_PREFIX) + 1)
> 
> There is no ring involved, so I guess it is some kind of copy-paste-search-replace error.
> 

I guess ring is involved in fact since the default mempool driver is
ring.

See drivers/mempool/ring/rte_mempool_ring.c ring_alloc().

Yes, it is not ideal, but at least it explains why RTE_RING_NAMESIZE
is used.

> 
> Looking at the rte_mempool structure [2]:
> struct __rte_cache_aligned rte_mempool {
> 	char name[RTE_MEMPOOL_NAMESIZE]; /**< Name of mempool. */
> 	union {
> 		void *pool_data;         /**< Ring or pool to store objects. */
> 		uint64_t pool_id;        /**< External mempool identifier. */
> 	};
> 
> 
> Due to the 8-byte alignment of the pool_id field following the name field, fixing the length as suggested doesn't change the memory layout for 64 bit CPU architectures.
> But it does for 32 bit CPU architectures, which will only 4-byte align the pool_id field.
> 
> [1]: https://elixir.bootlin.com/dpdk/v26.03-rc1/source/lib/mempool/rte_mempool.h#L128
> [2]: https://elixir.bootlin.com/dpdk/v26.03-rc1/source/lib/mempool/rte_mempool.h#L230
> 
> 
> Another thing:
> On 32 bit CPU architectures, the cache_size and local_cache fields in the rte_mempool structure are not in the same cache line.
> But I guess we don't really care about 32 bit CPU architectures.
> 
> 
> Venlig hilsen / Kind regards,
> -Morten Brørup
>