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To:     Oscar Salvador <osalvador@suse.de>
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        Andrew Morton <akpm@linux-foundation.org>,
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References: <20210322160200.19633-1-david@redhat.com>
 <20210322160200.19633-2-david@redhat.com> <20210324111835.GA18855@linux>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat GmbH
Subject: Re: [PATCH v1 1/3] kernel/resource: make walk_system_ram_res() find
 all busy IORESOURCE_SYSTEM_RAM resources
Message-ID: <8aa6af09-6f8b-1f50-820f-90eab0993f1c@redhat.com>
Date:   Wed, 24 Mar 2021 12:28:21 +0100
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On 24.03.21 12:18, Oscar Salvador wrote:
> On Mon, Mar 22, 2021 at 05:01:58PM +0100, David Hildenbrand wrote:
>> It used to be true that we can have busy system RAM only on the first level
>> in the resourc tree. However, this is no longer holds for driver-managed
>> system RAM (i.e., added via dax/kmem and virtio-mem), which gets added on
>> lower levels.
> 
> Let me ask some rookie questions:
> 
> What does "busy" term stand for here?

IORESOURCE_BUSY - here: actually added, not just some reserved range / container.


> Why resources coming from virtio-mem are added at a lower levels?

Some information can be had from ebf71552bb0e690cad523ad175e8c4c89a33c333

commit ebf71552bb0e690cad523ad175e8c4c89a33c333
Author: David Hildenbrand <david@redhat.com>
Date:   Thu May 7 16:01:35 2020 +0200

     virtio-mem: Add parent resource for all added "System RAM"
     
     Let's add a parent resource, named after the virtio device (inspired by
     drivers/dax/kmem.c). This allows user space to identify which memory
     belongs to which virtio-mem device.
     
     With this change and two virtio-mem devices:
             :/# cat /proc/iomem
             00000000-00000fff : Reserved
             00001000-0009fbff : System RAM
             [...]
             140000000-333ffffff : virtio0
               140000000-147ffffff : System RAM
               148000000-14fffffff : System RAM
               150000000-157ffffff : System RAM
             [...]
             334000000-3033ffffff : virtio1
               338000000-33fffffff : System RAM
               340000000-347ffffff : System RAM
               348000000-34fffffff : System RAM
             [...]


For dax/kmem it comes naturally due to the "Persistent Memory" and
device parent resources like:

             140000000-33fffffff : Persistent Memory
               140000000-1481fffff : namespace0.0
               150000000-33fffffff : dax0.0
                 150000000-33fffffff : System RAM (kmem)
             3280000000-32ffffffff : PCI Bus 0000:00


Thanks

-- 
Thanks,

David / dhildenb