Re: [dpdk-dev] [PATCH v4 2/4] mempool: add non-IO flag

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

On Fri, Oct 15, 2021 at 12:33:31PM +0300, Andrew Rybchenko wrote:
> On 10/15/21 12:18 PM, Dmitry Kozlyuk wrote:
> >> -----Original Message-----
> >> From: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>
> >> [...]
> >>> diff --git a/lib/mempool/rte_mempool.c b/lib/mempool/rte_mempool.c
> >>> index 51c0ba2931..2204f140b3 100644
> >>> --- a/lib/mempool/rte_mempool.c
> >>> +++ b/lib/mempool/rte_mempool.c
> >>> @@ -371,6 +371,8 @@ rte_mempool_populate_iova(struct rte_mempool *mp,
> >>> char *vaddr,
> >>>
> >>>       STAILQ_INSERT_TAIL(&mp->mem_list, memhdr, next);
> >>>       mp->nb_mem_chunks++;
> >>> +     if (iova == RTE_BAD_IOVA)
> >>> +             mp->flags |= MEMPOOL_F_NON_IO;
> >>
> >> As I understand rte_mempool_populate_iova() may be called few times for
> >> one mempool. The flag must be set if all invocations are done with
> >> RTE_BAD_IOVA. So, it should be set by default and just removed when iova
> >> != RTE_BAD_IOVA happens.
> > 
> > I don't agree at all. If any object of the pool is unsuitable for IO,
> > the pool cannot be considered suitable for IO. So if there's a single
> > invocation with RTE_BAD_IOVA, the flag must be set forever.
> 
> If so, some objects may be used for IO, some cannot be used.
> What should happen if an application allocates an object
> which is suitable for IO and try to use it this way?

If the application can predict if the allocated object is usable for IO
before allocating it, I would be surprised to have it used for IO. I agree
with Dmitry here.