Re: [dpdk-stable] [dpdk-dev] [PATCH v2] eal/linux: do not create user mem map repeatedly when it exists

[wangyunjian <wangyunjian@huawei.com>]

> -----Original Message-----
> From: Burakov, Anatoly [mailto:anatoly.burakov@intel.com]
> Sent: Friday, July 31, 2020 7:55 PM
> To: wangyunjian <wangyunjian@huawei.com>; dev@dpdk.org;
> david.marchand@redhat.com
> Cc: Lilijun (Jerry) <jerry.lilijun@huawei.com>; xudingke
> <xudingke@huawei.com>; stable@dpdk.org
> Subject: Re: [dpdk-dev] [PATCH v2] eal/linux: do not create user mem map
> repeatedly when it exists
> 
> On 30-Jul-20 2:16 PM, wangyunjian wrote:
> >> -----Original Message-----
> >> From: Burakov, Anatoly [mailto:anatoly.burakov@intel.com]
> >> Sent: Monday, July 27, 2020 5:24 PM
> >> To: wangyunjian <wangyunjian@huawei.com>; dev@dpdk.org;
> >> david.marchand@redhat.com
> >> Cc: Lilijun (Jerry) <jerry.lilijun@huawei.com>; xudingke
> >> <xudingke@huawei.com>; stable@dpdk.org
> >> Subject: Re: [dpdk-dev] [PATCH v2] eal/linux: do not create user mem map
> >> repeatedly when it exists
> >>
> >> On 25-Jul-20 10:59 AM, wangyunjian wrote:
> >>>> -----Original Message-----
> >>>> From: Burakov, Anatoly [mailto:anatoly.burakov@intel.com]
> >>>> Sent: Friday, July 24, 2020 9:25 PM
> >>>> To: wangyunjian <wangyunjian@huawei.com>; dev@dpdk.org;
> >>>> david.marchand@redhat.com
> >>>> Cc: Lilijun (Jerry) <jerry.lilijun@huawei.com>; xudingke
> >>>> <xudingke@huawei.com>; stable@dpdk.org
> >>>> Subject: Re: [dpdk-dev] [PATCH v2] eal/linux: do not create user mem
> >>>> map repeatedly when it exists
> >>>>
> >>>> On 23-Jul-20 3:48 PM, wangyunjian wrote:
> >>>>> From: Yunjian Wang <wangyunjian@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.
> >>>>>
> >>>>> To resolve the issue, add support to remove the same entry in the
> >>>>> function compact_user_maps().
> >>>>>
> >>>>> Fixes: 0cbce3a167f1 ("vfio: skip DMA map failure if already mapped")
> >>>>> Cc: stable@dpdk.org
> >>>>>
> >>>>> Signed-off-by: Yunjian Wang <wangyunjian@huawei.com>
> >>>>> ---
> >>>>> v2:
> >>>>> * Remove the same entry in the function compact_user_maps()
> >>>>> ---
> >>>>>     lib/librte_eal/linux/eal_vfio.c | 5 +++++
> >>>>>     1 file changed, 5 insertions(+)
> >>>>>
> >>>>> diff --git a/lib/librte_eal/linux/eal_vfio.c
> >>>>> b/lib/librte_eal/linux/eal_vfio.c index abb12a354..df99307b7 100644
> >>>>> --- a/lib/librte_eal/linux/eal_vfio.c
> >>>>> +++ b/lib/librte_eal/linux/eal_vfio.c
> >>>>> @@ -167,6 +167,10 @@ adjust_map(struct user_mem_map *src,
> struct
> >>>> user_mem_map *end,
> >>>>>     static int
> >>>>>     merge_map(struct user_mem_map *left, struct user_mem_map
> >> *right)
> >>>>>     {
> >>>>> +	/* merge the same maps into one */
> >>>>> +	if (memcmp(left, right, sizeof(struct user_mem_map)) == 0)
> >>>>> +		goto out;
> >>>>> +
> >>>>
> >>>> merge_map looks for adjacent maps only, but does not handle maps that
> >>>> are wholly contained within one another ("the same map" also matches
> >>>> this definition). wouldn't it be better to check for that instead of
> >>>> *just* handling identical maps?
> >>>
> >>> What about using the initial implementation?
> >>> We don't create new user mem map entry for the same memory segment.
> >>
> >> I don't like this implementation because it relies on particulars of how VFIO
> >> mapping work without explicitly specifying them. I.e. it's prone to breaking
> >> when changing code. That's not even mentioning that we have no
> guarantees
> >> on kernel behavior in that particular case being identical on all supported
> >> platforms.
> >>
> >> I would honestly prefer an explicit compaction over implicit one.
> >
> > What about this implementation?
> 
> Again, this works, but i feel like specializing it to just merge the
> exact same maps is missing an opportunity to provide a more general
> solution that merges same *and* subset maps.

Currently, the problem that I encounter is that a container has many
devices and the application will map the same memory many times.
The kernel driver returns EEXIST as long as there are overlapping memory
areas. Therefore, the application needs to ensure that the memory blocks
of the DMA do not overlap. Otherwise, it will not work normally.

Could you offer me some ideas or advise to fix it？

Thanks,
Yunjian
> 
> >
> > diff --git a/lib/librte_eal/linux/eal_vfio.c b/lib/librte_eal/linux/eal_vfio.c
> > index e07979936..8dcb04cd9 100644
> > --- a/lib/librte_eal/linux/eal_vfio.c
> > +++ b/lib/librte_eal/linux/eal_vfio.c
> > @@ -179,6 +179,19 @@ merge_map(struct user_mem_map *left, struct
> user_mem_map *right)
> >   	return 1;
> >   }
> >
> > +/* try merging two same maps into one, return 1 if succeeded */
> > +static int
> > +merge_same_map(struct user_mem_map *left, struct user_mem_map
> *right)
> > +{
> > +	if (memcmp(left, right, sizeof(struct user_mem_map)) != 0) {
> > +		return 0;
> > +	}
> > +
> > +	memset(right, 0, sizeof(*right));
> > +
> > +	return 1;
> > +}
> > +
> >   static struct user_mem_map *
> >   find_user_mem_map(struct user_mem_maps *user_mem_maps,
> uint64_t addr,
> >   		uint64_t iova, uint64_t len)
> > @@ -232,7 +245,7 @@ compact_user_maps(struct user_mem_maps
> *user_mem_maps)
> >   		if (is_null_map(l) || is_null_map(r))
> >   			continue;
> >
> > -		if (merge_map(l, r))
> > +		if (merge_map(l, r) || merge_same_map(l, r))
> >   			n_merged++;
> >   	}
> >
> > Thanks,
> > Yunjian
> >
> >>
> >>>
> >>> @@ -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;
> >>> +
> >>>    	/* create new user mem map entry */
> >>>    	new_map =
> >> &user_mem_maps->maps[user_mem_maps->n_maps++];
> >>>    	new_map->addr = vaddr;
> >>>
> >>> Thanks,
> >>> Yunjian
> >>>>
> >>>>>     	if (left->addr + left->len != right->addr)
> >>>>>     		return 0;
> >>>>>     	if (left->iova + left->len != right->iova) @@ -174,6 +178,7 @@
> >>>>> merge_map(struct user_mem_map *left, struct
> >>>> user_mem_map *right)
> >>>>>
> >>>>>     	left->len += right->len;
> >>>>>
> >>>>> +out:
> >>>>>     	memset(right, 0, sizeof(*right));
> >>>>>
> >>>>>     	return 1;
> >>>>>
> >>>>
> >>>>
> >>>> --
> >>>> Thanks,
> >>>> Anatoly
> >>
> >>
> >> --
> >> Thanks,
> >> Anatoly
> 
> 
> --
> Thanks,
> Anatoly