RE: mempool name size incorrect?

["Morten Brørup" <mb@smartsharesystems.com>]

> From: Andrew Rybchenko [mailto:andrew.rybchenko@oktetlabs.ru]
> Sent: Wednesday, 11 March 2026 10.47
> 
> 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.

Thanks, that explains it. Bad layer violation...
Let's hope no future mempool driver adds anything longer than "RG_" to the name of any memzone it creates.

Looking into the associated string length checks, using a too long name will fail with ENAMETOOLONG.
So, using a long mempool name might succeed with some mempool drivers and fail with others. :-(

I guess there's no simple fix for that.
And I was wrong to think that the RTE_MEMPOOL_NAMESIZE should be increased from 26 to 29.

> 
> >
> > 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
> >