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Date: Tue, 16 Jan 2018 14:51:55 +0100
From: Olivier Matz <olivier.matz@6wind.com>
To: Hemant Agrawal <hemant.agrawal@nxp.com>
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Subject: Re: [dpdk-dev] [PATCH 1/2] mempool: indicate the usages of multi
	memzones
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On Fri, Dec 22, 2017 at 09:48:01PM +0530, Hemant Agrawal wrote:
> On 12/22/2017 7:29 PM, Olivier MATZ wrote:
> > On Wed, Dec 20, 2017 at 05:29:59PM +0530, Hemant Agrawal wrote:
> > > On 12/19/2017 6:38 PM, Hemant Agrawal wrote:
> > > > 
> > > > > That's true, I commented too fast :)
> > > > > And what about using mp->nb_mem_chunks instead? Would it do the job
> > > > > in your use-case?
> > > > 
> > > > It should work.  Let me check it out.
> > > 
> > > There is a slight problem with nb_mem_chunks.
> > > 
> > > It is getting incremented in the end of "rte_mempool_populate_phys",
> > > while the elements are getting populated before it in the call of
> > > mempool_add_elem.
> > > 
> > > I can use nb_mem_chunks are '0' check. However it can break in future if
> > > mempool_populate_phys changes.
> > 
> > Sorry, I'm not sure I'm getting what you say.
> > 
> > My question was about using mp->nb_mem_chunks instead of a new flag in the
> > dppa driver. Am I missing something?
> > 
> 
> mp->nb_mem_chunks gets finalized when the mempool is fully created. It's
> value is transient before that i.e. it will keep on changing on the every
> call to rte_mempool_populate_phys.
> 
> However, we need this information on the very first element allocation. So,
> nb_mem_chunks will not work.

I see 2 other alternatives:

1/ in your driver, register a callback rte_mempool_ops_register_memory_area()
   that sets a private flag if (len < total_elt_sz * mp->size).

2/ Move
    STAILQ_INSERT_TAIL(&mp->mem_list, memhdr, next);
    mp->nb_mem_chunks++;
   before the calls to mempool_add_elem(), and in your driver check if
   SLIST_FIRST(&mp->mem_list)->len < total_elt_sz * mp->size

If we can avoid to again create another flag, it is better.