> From: Konstantin Ananyev [mailto:[email protected]]
> Sent: Wednesday, 11 March 2026 11.52
>
> > > 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.
I assume the names are allocated as part of the structures to make them part of
the shared memory, to be searchable by secondary processes.
I guess someone once thought 32 characters would be enough.
Furthermore, these startup-only parts of the structures really should be
clearly marked as such, to ensure that they remain in dedicated cache lines,
not mixed with hot fields in the same structures.
As I mentioned below, when building for 32 bit architectures, the cache_size
field - which is accessed by the mempool fastpath functions - is in a cache
line shared with the name, instead of the cache line with the local_cache field
pointing to the local cache; i.e. causing two cache misses instead of one, when
getting or putting objects from/to a mempool cache.
I agree that this should be cleaned up at a future big API breakage.
>
> > >
> > > >
> > > > 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
> > > >
