RE: mempool name size incorrect?

[Konstantin Ananyev <konstantin.ananyev@huawei.com>]

> > 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.

As a generic thought: might be it is time to make the length across these
structs (mempool, ring, etc.) arbitrary?
At our next big API breakage or so.

> >
> > >
> > > 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
> > >