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

["Burakov, Anatoly" <anatoly.burakov@intel.com>]

On 17-Jul-20 3:19 PM, Burakov, Anatoly wrote:
> On 16-Jul-20 2:38 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.
>>
>> Fixes: 0cbce3a167f1 ("vfio: skip DMA map failure if already mapped")
>> Cc: stable@dpdk.org
>>
>> Signed-off-by: Yunjian Wang <wangyunjian@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?

-- 
Thanks,
Anatoly