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SubjectRe: [RFC 5/8] mm: Add new flag VM_CDM for coherent device memory

On 25/10/16 04:38, Dave Hansen wrote:
> On 10/23/2016 09:31 PM, Anshuman Khandual wrote:
>> VMAs containing coherent device memory should be marked with VM_CDM. These
>> VMAs need to be identified in various core kernel paths and this new flag
>> will help in this regard.
> ... and it's sticky? So if a VMA *ever* has one of these funky pages in
> it, it's stuck being VM_CDM forever? Never to be merged with other
> VMAs? Never to see the light of autonuma ever again?
> What if a 100TB VMA has one page of fancy pants device memory, and the
> rest normal vanilla memory? Do we really want to consider the whole
> thing fancy?

Those are good review comments to improve the patchset.

> This whole patch set is looking really hackish. If you want things to
> be isolated from the VM, them it should probably *actually* be isolated
> from the VM. As Jerome mentioned, ZONE_DEVICE is probably a better
> thing to use here than to try what you're attempting.

The RFC explains the motivation, this is not fancy pants, it is regular
memory from the systems perspective, with some changes as described

Thanks for the review!
Balbir Singh

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