From: "Ananyev, Konstantin" <konstantin.ananyev@intel.com>
To: Olivier MATZ <olivier.matz@6wind.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 10:47:50 +0000 [thread overview]
Message-ID: <2601191342CEEE43887BDE71AB977258213F749B@irsmsx105.ger.corp.intel.com> (raw)
In-Reply-To: <550A850D.9010309@6wind.com>
Hi Olivier,
> -----Original Message-----
> From: Olivier MATZ [mailto:olivier.matz@6wind.com]
> Sent: Thursday, March 19, 2015 8:13 AM
> To: Ananyev, Konstantin; vadim.suraev@gmail.com
> Cc: dev@dpdk.org
> Subject: Re: [dpdk-dev] [PATCH v2] rte_mbuf: mbuf bulk alloc/free functions added + unittest
>
> 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?
The scenario you described would work I believe, as second reference for m1 is from indirect mbuf.
So rte_pktmbuf_free(clone1) would just call __rte_mbuf_raw_free(m1).
The scenario I am talking about is:
No indirect mbufs pointing to m1 data buffer.
m1->next == m2; m1->refcnt==2;
m2->next == NULL; m2->rectn==1;
And then:
rte_pktmbuf_free(m1); //after that m2 is freed, but m1->next == m2
rte_pktmbuf_free(m1); //would call rte_pktmbuf_free_seg(m2)
That one would not work correctly, and I think considered as invalid case right now.
Konstantin
>
> Thanks,
> Olivier
next prev parent reply other threads:[~2015-03-19 10:49 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
2015-03-19 10:47 ` Ananyev, Konstantin [this message]
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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