[dpdk-dev] [PATCH 1/1] eal/linux: do not create user mem map repeatedly when it exists

wangyunjian wangyunjian at huawei.com
Mon Jul 20 04:00:48 CEST 2020


> -----Original Message-----
> From: Burakov, Anatoly [mailto:anatoly.burakov at intel.com]
> Sent: Friday, July 17, 2020 10:24 PM
> To: wangyunjian <wangyunjian at huawei.com>; dev at dpdk.org;
> david.marchand at redhat.com
> Cc: Lilijun (Jerry) <jerry.lilijun at huawei.com>; xudingke
> <xudingke at huawei.com>; stable at dpdk.org
> Subject: Re: [dpdk-dev] [PATCH 1/1] eal/linux: do not create user mem map
> repeatedly when it exists
> 
> On 17-Jul-20 3:19 PM, Burakov, Anatoly wrote:
> > On 16-Jul-20 2:38 PM, wangyunjian wrote:
> >> From: Yunjian Wang <wangyunjian at huawei.com>
> >>
> >> Currently, we will create new user mem map entry for the same memory
> >> segment, but in fact it has already been added to the user mem maps.
> >> It's not necessary to create it twice.
> >>
> >> Fixes: 0cbce3a167f1 ("vfio: skip DMA map failure if already mapped")
> >> Cc: stable at dpdk.org
> >>
> >> Signed-off-by: Yunjian Wang <wangyunjian at huawei.com>
> >> ---
> >>   lib/librte_eal/linux/eal_vfio.c | 7 +++++++
> >>   1 file changed, 7 insertions(+)
> >>
> >> diff --git a/lib/librte_eal/linux/eal_vfio.c
> >> b/lib/librte_eal/linux/eal_vfio.c index abb12a354..d8a8c39ab 100644
> >> --- a/lib/librte_eal/linux/eal_vfio.c
> >> +++ b/lib/librte_eal/linux/eal_vfio.c
> >> @@ -1828,6 +1828,13 @@ container_dma_map(struct vfio_config
> >> *vfio_cfg, uint64_t vaddr, uint64_t iova,
> >>           ret = -1;
> >>           goto out;
> >>       }
> >> +
> >> +    /* we don't need create new user mem map entry
> >> +     * for the same memory segment.
> >> +     */
> >> +    if (errno == EBUSY || errno == EEXIST)
> >> +        goto out;
> >> +
> >
> > I'm not sure i understand this patch. If we get errno, the call has
> > failed, which means we're doing "goto out" from a few lines above. Am
> > i missing something here?
> >
> >>       /* create new user mem map entry */
> >>       new_map =
> &user_mem_maps->maps[user_mem_maps->n_maps++];
> >>       new_map->addr = vaddr;
> >>
> >
> >
> 
> Oh, i see, the actual functions will set errno and return 0.
> 
> I don't think it's an actual issue as compacting will presumably remove the
> extra user mem map anyway. What exactly is being fixed here? Does
> compacting user mem maps not remove the extra entry?

I read the codes about compacting user mem maps. Currently, the function
only merges adjacent user mem maps and does not remove the same entry.

How about removing the same entry in the fuction?

Thanks
Yunjian

> 
> --
> Thanks,
> Anatoly


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