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From: Olivier MATZ <olivier.matz@6wind.com>
To: Neil Horman <nhorman@tuxdriver.com>,
	 "vadim.suraev@gmail.com" <vadim.suraev@gmail.com>
Cc: dev@dpdk.org
Subject: Re: [dpdk-dev] [PATCH v2] rte_mbuf: mbuf bulk alloc/free functions added + unittest
Date: Thu, 19 Mar 2015 09:41:25 +0100
Message-ID: <550A8BB5.9040104@6wind.com> (raw)
In-Reply-To: <20150318205856.GA5151@neilslaptop.think-freely.org>

Hi Neil,

On 03/18/2015 09:58 PM, Neil Horman wrote:
>> +/**
>> + * Free a bulk of mbufs into its original mempool.
>> + * This function assumes:
>> + * - refcnt equals 1
>> + * - mbufs are direct
>> + * - all mbufs must belong to the same mempool
>> + *
>> + * @param mbufs
>> + *    Array of pointers to mbuf
>> + * @param count
>> + *    Array size
>> + */
>> +static inline void rte_pktmbuf_bulk_free(struct rte_mbuf **mbufs,
>> +					 unsigned count)
>> +{
>> +	unsigned idx;
>> +
>> +	RTE_MBUF_ASSERT(count > 0);
>> +
>> +	for (idx = 0; idx < count; idx++) {
>> +		RTE_MBUF_ASSERT(mbufs[idx]->pool == mbufs[0]->pool);
>> +		RTE_MBUF_ASSERT(rte_mbuf_refcnt_read(mbufs[idx]) == 1);
>> +		rte_mbuf_refcnt_set(mbufs[idx], 0);
> This is really a misuse of the API.  The entire point of reference counting is
> to know when an mbuf has no more references and can be freed.  By forcing all
> the reference counts to zero here, you allow the refcnt infrastructure to be
> circumvented, causing memory leaks.
>
> I think what you need to do here is enhance the underlying pktmbuf interface
> such that an rte_mbuf structure has a destructor method association with it
> which is called when its refcnt reaches zero.  That way the
> rte_pktmbuf_bulk_free function can just decrement the refcnt on each
> mbuf_structure, and the pool as a whole can be returned when the destructor
> function discovers that all mbufs in that bulk pool are freed.

I don't really understand what's the problem here. The API explicitly
describes the conditions for calling this functions: the segments are
directs, they belong to the same mempool, and their refcnt is 1.

This function could be useful in a driver which knows that the mbuf
it allocated matches this conditions. I think an application that
only uses direct mbufs and one mempool could also use this function.

Regards,
Olivier

  reply	other threads:[~2015-03-19  8:41 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-03-18 20:21 vadim.suraev
2015-03-18 20:58 ` Neil Horman
2015-03-19  8:41   ` Olivier MATZ [this message]
2015-03-19 10:06     ` Ananyev, Konstantin
2015-03-19 13:16     ` Neil Horman
2015-03-23 16:44       ` Olivier MATZ
2015-03-23 17:31         ` Vadim Suraev
2015-03-23 23:48           ` Ananyev, Konstantin
2015-03-24  7:53             ` Vadim Suraev
     [not found]               ` <2601191342CEEE43887BDE71AB977258214071C0@irsmsx105.ger.corp.intel.com>
2015-03-24 11:00                 ` Ananyev, Konstantin
2015-03-23 18:45         ` Neil Horman
2015-03-30 19:04   ` Vadim Suraev
2015-03-30 20:15     ` Neil Horman
  -- strict thread matches above, loose matches on Subject: below --
2015-03-17 21:36 vadim.suraev
2015-03-17 23:46 ` Ananyev, Konstantin
2015-03-18  5:19   ` Vadim Suraev
     [not found]     ` <2601191342CEEE43887BDE71AB977258213F7053@irsmsx105.ger.corp.intel.com>
2015-03-18  9:56       ` Ananyev, Konstantin
2015-03-18 10:41         ` Vadim Suraev
     [not found]           ` <2601191342CEEE43887BDE71AB977258213F7136@irsmsx105.ger.corp.intel.com>
2015-03-18 15:13             ` Ananyev, Konstantin
2015-03-19  8:13               ` Olivier MATZ
2015-03-19 10:47                 ` Ananyev, Konstantin
2015-03-19 10:54                   ` Olivier MATZ

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