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: 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?

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