[Question] mm/resource: a mistake to use IORESOURCE_SYSRAM instead of IORESOURCE_SYSTEM_RAM?

[Eric Ren <renzhengeek@gmail.com>]

Hi David,

I feel confused on this piece of code:

```
void release_mem_region_adjustable(resource_size_t start, 
resource_size_t size)
{
... snip
/*
          * All memory regions added from memory-hotplug path have the
          * flag IORESOURCE_SYSTEM_RAM. If the resource does not have
          * this flag, we know that we are dealing with a resource coming
          * from HMM/devm. HMM/devm use another mechanism to add/release
          * a resource. This goes via devm_request_mem_region and
          * devm_release_mem_region.
          * HMM/devm take care to release their resources when they want,
          * so if we are dealing with them, let us just back off here.
          */
         if (!(res->flags & IORESOURCE_SYSRAM)) {
             break;
         }
```

The comment says IORESOURCE_SYSTEM_RAM while IORESOURCE_SYSRAM is 
actually used.
Is this a mistake?

The reason why I come to read about this is that, I got -EEXIST error from
add_memory_driver_managed() when I want to virtio_mem regions sitting on 
Reserved
memory region like this in /proc/iomem:
```
fffc0000-183fffffff : Reserved
   100000000-183fffffff : System RAM (virtio_mem)
     1820000000-183fffffff : System RAM (virtio_mem) // --> plugged MB
```

EEXIST error happens after plug -> unplug -> plug testing, because the
hot-added region remains after unplug. The hot-added region is under
Reserved region. The IORESOURCE_SYSRAM flag check will skips to handle
children of the Reserved region.
Thanks in advance!
Eric