From: Anshuman Khandual <khandual@linux.vnet.ibm.com>
To: Jerome Glisse <jglisse@redhat.com>, Dave Hansen <dave.hansen@intel.com>
Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
linux-mm@kvack.org, John Hubbard <jhubbard@nvidia.com>,
Dan Williams <dan.j.williams@intel.com>,
Ross Zwisler <ross.zwisler@linux.intel.com>
Subject: Re: [HMM v14 05/16] mm/ZONE_DEVICE/unaddressable: add support for un-addressable device memory
Date: Mon, 26 Dec 2016 14:42:07 +0530 [thread overview]
Message-ID: <5860DEE7.5040505@linux.vnet.ibm.com> (raw)
In-Reply-To: <2093258630.3273244.1481229443563.JavaMail.zimbra@redhat.com>
On 12/09/2016 02:07 AM, Jerome Glisse wrote:
>> On 12/08/2016 08:39 AM, Jerome Glisse wrote:
>>>> > >> On 12/08/2016 08:39 AM, JA(C)rA'me Glisse wrote:
>>>>>>> > >>> > > Architecture that wish to support un-addressable device memory should
>>>>>>> > >>> > > make
>>>>>>> > >>> > > sure to never populate the kernel linar mapping for the physical
>>>>>>> > >>> > > range.
>>>>> > >> >
>>>>> > >> > Does the platform somehow provide a range of physical addresses for this
>>>>> > >> > unaddressable area? How do we know no memory will be hot-added in a
>>>>> > >> > range we're using for unaddressable device memory, for instance?
>>> > > That's what one of the big issue. No platform does not reserve any range so
>>> > > there is a possibility that some memory get hotpluged and assign this
>>> > > range.
>>> > >
>>> > > I pushed the range decision to higher level (ie it is the device driver
>>> > > that
>>> > > pick one) so right now for device driver using HMM (NVidia close driver as
>>> > > we don't have nouveau ready for that yet) it goes from the highest physical
>>> > > address and scan down until finding an empty range big enough.
>> >
>> > I don't think you should be stealing physical address space for things
>> > that don't and can't have physical addresses. Delegating this to
>> > individual device drivers and hoping that they all get it right seems
>> > like a recipe for disaster.
> Well i expected device driver to use hmm_devmem_add() which does not take
> physical address but use the above logic to pick one.
>
>> >
>> > Maybe worth adding to the changelog:
>> >
>> > This feature potentially breaks memory hotplug unless every
>> > driver using it magically predicts the future addresses of
>> > where memory will be hotplugged.
> I will add debug printk to memory hotplug in case it fails because of some
> un-addressable resource. If you really dislike memory hotplug being broken
> then i can go down the way of allowing to hotplug memory above the max
> physical memory limit. This require more changes but i believe this is
> doable for some of the memory model (sparsemem and sparsemem extreme).
Did not get that. Hotplug memory request will come within the max physical
memory limit as they are real RAM. The address range also would have been
specified. How it can be added beyond the physical limit irrespective of
which we memory model we use.
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next prev parent reply other threads:[~2016-12-26 9:12 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-08 16:39 [HMM v14 00/16] HMM (Heterogeneous Memory Management) v14 Jérôme Glisse
2016-12-08 16:39 ` [HMM v14 01/16] mm/free_hot_cold_page: catch ZONE_DEVICE pages Jérôme Glisse
2016-12-08 16:39 ` [HMM v14 02/16] mm/memory/hotplug: convert device bool to int to allow for more flags v2 Jérôme Glisse
2016-12-08 16:39 ` [HMM v14 03/16] mm/ZONE_DEVICE/devmem_pages_remove: allow early removal of device memory Jérôme Glisse
2016-12-08 16:39 ` [HMM v14 04/16] mm/ZONE_DEVICE/free-page: callback when page is freed Jérôme Glisse
2016-12-08 16:39 ` [HMM v14 05/16] mm/ZONE_DEVICE/unaddressable: add support for un-addressable device memory Jérôme Glisse
2016-12-08 16:21 ` Dave Hansen
2016-12-08 16:39 ` Jerome Glisse
2016-12-08 20:07 ` Dave Hansen
2016-12-08 20:37 ` Jerome Glisse
2016-12-26 9:12 ` Anshuman Khandual [this message]
2016-12-26 19:02 ` Jerome Glisse
2016-12-08 16:39 ` [HMM v14 06/16] mm/ZONE_DEVICE/x86: " Jérôme Glisse
2016-12-08 16:39 ` [HMM v14 07/16] mm/hmm: heterogeneous memory management (HMM for short) Jérôme Glisse
2016-12-08 16:39 ` [HMM v14 08/16] mm/hmm/mirror: mirror process address space on device with HMM helpers Jérôme Glisse
2016-12-08 16:39 ` [HMM v14 09/16] mm/hmm/mirror: helper to snapshot CPU page table Jérôme Glisse
2016-12-08 16:39 ` [HMM v14 10/16] mm/hmm/mirror: device page fault handler Jérôme Glisse
2016-12-08 16:39 ` [HMM v14 11/16] mm/hmm/migrate: support un-addressable ZONE_DEVICE page in migration Jérôme Glisse
2016-12-08 16:39 ` [HMM v14 12/16] mm/hmm/migrate: add new boolean copy flag to migratepage() callback Jérôme Glisse
2016-12-08 16:39 ` [HMM v14 13/16] mm/hmm/migrate: new memory migration helper for use with device memory v2 Jérôme Glisse
2016-12-08 16:39 ` [HMM v14 14/16] mm/hmm/migrate: optimize page map once in vma being migrated Jérôme Glisse
2016-12-08 16:39 ` [HMM v14 15/16] mm/hmm/devmem: device driver helper to hotplug ZONE_DEVICE memory Jérôme Glisse
2016-12-08 16:39 ` [HMM v14 16/16] mm/hmm/devmem: dummy HMM device as an helper for " Jérôme Glisse
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