Re: [PATCH v2 2/3] mm/hmm: allow snapshot of the special zero page

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On Tue, Oct 22, 2019 at 01:30:26PM -0400, Jerome Glisse wrote:

> > Smart drivers can test somehow for pfn == zero_page and optimize?
> 
> There is nothing to optimize here, i do not know any hardware that
> have a special page table entry that make all memory access return
> zero.

Presumably any GPU could globally dedicate one page of internal memory
as a zero page and remap CPU zero page to that internal memory page?
This is basically how the CPU zero page works.

I suspect mlx5 could do the same with its internal memory, but the
internal memory is too limited to make this worth while.

mlx5 also has a specially 'zero MR' that always reads as zero (and
discards writes), but it doesn't quite fit well into the ODP flow.

Jason





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