From: Jerome Glisse <jglisse@redhat.com>
To: Jason Gunthorpe <jgg@mellanox.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>,
John Hubbard <jhubbard@nvidia.com>,
Christoph Hellwig <hch@lst.de>,
"linux-rdma@vger.kernel.org" <linux-rdma@vger.kernel.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>
Subject: Re: [PATCH v2 2/3] mm/hmm: allow snapshot of the special zero page
Date: Tue, 22 Oct 2019 13:52:59 -0400 [thread overview]
Message-ID: <20191022175259.GA5942@redhat.com> (raw)
In-Reply-To: <20191022174107.GM22766@mellanox.com>
On Tue, Oct 22, 2019 at 05:41:11PM +0000, Jason Gunthorpe wrote:
> 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.
Yes that would work too but i do not know of any upstream driver
that does that.
> 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.
Well you can always ask for new stuff to your beloved hardware
engineers, they never say no right ? :)
Cheers,
Jérôme
next prev parent reply other threads:[~2019-10-22 17:53 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-15 20:48 [PATCH v2 0/3] HMM tests and minor fixes Ralph Campbell
2019-10-15 20:48 ` [PATCH v2 1/3] mm/hmm: make full use of walk_page_range() Ralph Campbell
2019-10-21 18:32 ` Jason Gunthorpe
2019-10-21 20:32 ` Ralph Campbell
2019-10-15 20:48 ` [PATCH v2 2/3] mm/hmm: allow snapshot of the special zero page Ralph Campbell
2019-10-21 18:08 ` Jason Gunthorpe
2019-10-21 20:08 ` Ralph Campbell
2019-10-21 18:49 ` Jerome Glisse
2019-10-21 20:54 ` Ralph Campbell
2019-10-22 2:45 ` Jerome Glisse
2019-10-22 15:05 ` Jason Gunthorpe
2019-10-22 17:06 ` Jerome Glisse
2019-10-22 17:09 ` Jason Gunthorpe
2019-10-22 17:30 ` Jerome Glisse
2019-10-22 17:41 ` Jason Gunthorpe
2019-10-22 17:52 ` Jerome Glisse [this message]
2019-10-15 20:48 ` [PATCH v2 3/3] mm/hmm/test: add self tests for HMM Ralph Campbell
2019-10-21 18:50 ` Jerome Glisse
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