DPDK 22.11 - How to fix memory leak for KNI - How to debug

[Yasin CANER]

Hello Ferruh,

Thanks for your kind response. Also thanks to Stephen.

Even if 1 packet is consumed from the kernel , each time rx_kni allocates
another 32 units. After a while all mempool is used in alloc_q from kni.
there is not any room for it.

Do you think my mistake is using one and common mempool usage both kni and
eth?

If it needs a separate mempool , i'd like to note in docs.

Best regards.

Ferruh Yigit <ferruh.yigit at amd.com>, 17 May 2023 Çar, 20:53 tarihinde şunu
yazdı:

> On 5/9/2023 12:13 PM, Yasin CANER wrote:
> > Hello,
> >
> > I draw a flow via asciiflow to explain myself better. Problem is after
> > transmitting packets(mbufs) , it never puts in the kni->free_q to back
> > to the original pool. Each cycle, it allocates another 32 units that
> > cause leaks. Or I am missing something.
> >
> > I already tried the rte_eth_tx_done_cleanup() function but it didn't fix
> > anything.
> >
> > I am working on a patch to fix this issue but I am not sure if there
> > is another way.
> >
> > Best regards.
> >
> > https://pastebin.ubuntu.com/p/s4h5psqtgZ/
> > <https://pastebin.ubuntu.com/p/s4h5psqtgZ/>
> >
> >
> > unsigned
> > rte_kni_rx_burst(struct rte_kni *kni, struct rte_mbuf **mbufs, unsigned
> > int num)
> > {
> > unsigned int ret = kni_fifo_get(kni->tx_q, (void **)mbufs, num);
> >
> > /* If buffers removed, allocate mbufs and then put them into alloc_q */
> > /* Question, how to test buffers is removed or not?*/
> > if (ret)
> >     kni_allocate_mbufs(kni);
> >
> > return ret;
> > }
> >
>
> Selam Yasin,
>
>
> You can expect 'kni->alloc_q' fifo to be full, this is not a memory leak.
>
> As you pointed out, number of mbufs consumed by kernel from 'alloc_q'
> and number of mbufs added to 'alloc_q' is not equal and this is expected.
>
> Target here is to prevent buffer underflow from kernel perspective, so
> it will always have available mbufs for new packets.
> That is why new mbufs are added to 'alloc_q' at worst same or sometimes
> higher rate than it is consumed.
>
> You should calculate your mbuf requirement with the assumption that
> 'kni->alloc_q' will be full of mbufs.
>
>
> 'kni->alloc_q' is freed when kni is removed.
> Since 'alloc_q' holds physical address of the mbufs, it is a little
> challenging to free them in the userspace, that is why first kernel
> tries to move mbufs to 'kni->free_q' fifo, please check
> 'kni_net_release_fifo_phy()' for it.
>
> If all moved to 'free_q' fifo, nothing left to in 'alloc_q', but if not,
> userspace frees 'alloc_q' in 'rte_kni_release()', with following call:
> `kni_free_fifo_phy(kni->pktmbuf_pool, kni->alloc_q);`
>
>
> I can see you have submitted fixes for this issue, although as I
> explained above I don't think a defect exist, I will review them
> today/tomorrow.
>
> Regards,
> Ferruh
>
>
> > Stephen Hemminger <stephen at networkplumber.org
> > <mailto:stephen at networkplumber.org>>, 8 May 2023 Pzt, 19:18 tarihinde
> > şunu yazdı:
> >
> >     On Mon, 8 May 2023 09:01:41 +0300
> >     Yasin CANER <yasinncaner at gmail.com <mailto:yasinncaner at gmail.com>>
> >     wrote:
> >
> >     > Hello Stephen,
> >     >
> >     > Thank you for response, it helps me a lot. I understand problem
> >     better.
> >     >
> >     > After reading mbuf library (
> >     > https://doc.dpdk.org/guides/prog_guide/mempool_lib.html
> >     <https://doc.dpdk.org/guides/prog_guide/mempool_lib.html>)  i
> >     realized that
> >     > 31 units allocation memory slot doesn't return to pool!
> >
> >     If receive burst returns 1 mbuf, the other 31 pointers in the array
> >     are not valid. They do not point to mbufs.
> >
> >     > 1 unit mbuf can be freed via rte_pktmbuf_free so it can back to
> pool.
> >     >
> >     > Main problem is that allocation doesn't return to original pool,
> >     act as
> >     > used. So, after following rte_pktmbuf_free
> >     >
> >     <
> http://doc.dpdk.org/api/rte__mbuf_8h.html#a1215458932900b7cd5192326fa4a6902
> <
> http://doc.dpdk.org/api/rte__mbuf_8h.html#a1215458932900b7cd5192326fa4a6902
> >>
> >     > function,
> >     > i realized that there is 2 function to helps to mbufs back to pool.
> >     >
> >     > These are rte_mbuf_raw_free
> >     >
> >     <
> http://doc.dpdk.org/api/rte__mbuf_8h.html#a9f188d53834978aca01ea101576d7432
> <
> http://doc.dpdk.org/api/rte__mbuf_8h.html#a9f188d53834978aca01ea101576d7432
> >>
> >     >  and rte_pktmbuf_free_seg
> >     >
> >     <
> http://doc.dpdk.org/api/rte__mbuf_8h.html#a006ee80357a78fbb9ada2b0432f82f37
> <
> http://doc.dpdk.org/api/rte__mbuf_8h.html#a006ee80357a78fbb9ada2b0432f82f37
> >>.
> >     > I will focus on them.
> >     >
> >     > If there is another suggestion, I will be very pleased.
> >     >
> >     > Best regards.
> >     >
> >     > Yasin CANER
> >     > Ulak
> >
>
>
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