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From: Olivier MATZ <olivier.matz@6wind.com>
To: "Ananyev, Konstantin" <konstantin.ananyev@intel.com>,
	 "vadim.suraev@gmail.com" <vadim.suraev@gmail.com>
Cc: "dev@dpdk.org" <dev@dpdk.org>
Subject: Re: [dpdk-dev] [PATCH v2] rte_mbuf: mbuf bulk alloc/free functions added + unittest
Date: Thu, 19 Mar 2015 09:13:01 +0100
Message-ID: <550A850D.9010309@6wind.com> (raw)
In-Reply-To: <2601191342CEEE43887BDE71AB977258213F7188@irsmsx105.ger.corp.intel.com>

Hi Konstantin,

On 03/18/2015 04:13 PM, Ananyev, Konstantin wrote:
>
>> From: Vadim Suraev [mailto:vadim.suraev@gmail.com]
>> Sent: Wednesday, March 18, 2015 10:41 AM
>> To: Ananyev, Konstantin
>> Cc: dev@dpdk.org
>> Subject: Re: [PATCH v2] rte_mbuf: mbuf bulk alloc/free functions added + unittest
>>
>> Hi, Konstantin,
>>
>> Got it. To make the same, nulling the next should be inside of the block as you said.
>> One question raises here: If a segment in the chain has refcnt > 1 (so its next is not assigned NULL), and the next segment has refcnt
>> == 1 (so it is freed), do you think this scenario is real/should be considered? If so, the former can be safely freed only by calling
>> rte_pktmbuf_free_seg which does not iterate. So why to keep next pointing to something?
>
> I think we need it, not just to keep things the same with  rte_pktmbuf_free(), but because it is a right thing to do.
> Let say you have a packet in 2 mbufs chained together, both mbufs have refcnt==2.
> Then:
> rte_pktmbuf_free(firs_mbuf);
> rte_pktmbuf_free(firs_mbuf);
>
> Would work correctly and free both mbufs back to the mempool.
>
> While after:
> rte_pktmbuf_free_chain(first_mbuf);
> rte_pktmbuf_free_chain(first_mbuf);
>
> We would have first_mbuf freed back into the mempool, while second would get lost(memory leaking).
> Basically free() shouldn't modify any filed inside mbuf, except refcnt if rte_mbuf_refcnt_update(m, -1) > 0
>
> About your case, when: first_mbuf->refcnt==2 and second_mbuf->refcnt==1.
> Right now, rte_pktmbuf_free() can't handle such cases properly,
> and, as I know, such situation is not considered as valid one.

I'm not sure I understand what you are saying. To me, the case you are
describing is similar to the case below, and it should work properly:

	/* allocate a packet and clone it. After that, m1 has a
	 * refcnt of 2 */
	m1 = rte_pktmbuf_alloc();
	clone1 = rte_pktmbuf_clone(m1);

	/* allocate another packet */
	m2 = rte_pktmbuf_alloc();

	/* chain m2 after m1, updating fields like total length.
	 * After that, m1 has 2 segments, the first one has a refcnt
	 * of 1 and the second has a refcnt of 2 */
	mbuf_concat(m1, m2);

	/* This will decrement the refcnt on the first segment and
	 * free the second segment */
	rte_pktmbuf_free(m1);

	/* free the indirect mbuf, and as the refcnt is 1 on the
	 * direct mbuf (m1), also release it */
	rte_pktmbuf_free(clone1);

Am I missing something?

Thanks,
Olivier

  reply	other threads:[~2015-03-19  8:13 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
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 [this message]
2015-03-19 10:47                 ` Ananyev, Konstantin
2015-03-19 10:54                   ` Olivier MATZ
2015-03-18 20:21 vadim.suraev
2015-03-18 20:58 ` Neil Horman
2015-03-19  8:41   ` Olivier MATZ
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

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