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Subject: Re: [PATCH v3 3/6] mm: support THP migration to device private memory
To:     Christoph Hellwig <hch@lst.de>
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From:   Ralph Campbell <rcampbell@nvidia.com>
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On 11/9/20 1:14 AM, Christoph Hellwig wrote:
> On Fri, Nov 06, 2020 at 01:26:50PM -0800, Ralph Campbell wrote:
>>
>> On 11/6/20 12:03 AM, Christoph Hellwig wrote:
>>> I hate the extra pin count magic here.  IMHO we really need to finish
>>> off the series to get rid of the extra references on the ZONE_DEVICE
>>> pages first.
>>
>> First, thanks for the review comments.
>>
>> I don't like the extra refcount either, that is why I tried to fix that up
>> before resending this series. However, you didn't like me just fixing the
>> refcount only for device private pages and I don't know the dax/pmem code
>> and peer-to-peer PCIe uses of ZONE_DEVICE pages well enough to say how
>> long it will take me to fix all the use cases.
>> So I wanted to make progress on the THP migration code in the mean time.
> 
> I think P2P is pretty trivial, given that ZONE_DEVICE pages are used like
> a normal memory allocator.  DAX is the interesting case, any specific
> help that you need with that?

Thanks for the offer. I'm putting a list together... :-)