From: Jason Gunthorpe <jgg@mellanox.com>
To: Ralph Campbell <rcampbell@nvidia.com>
Cc: Jerome Glisse <jglisse@redhat.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>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v3 3/3] mm/hmm/test: add self tests for HMM
Date: Thu, 31 Oct 2019 17:34:42 +0000 [thread overview]
Message-ID: <20191031173438.GL22766@mellanox.com> (raw)
In-Reply-To: <a6b49a4e-a194-ce0b-685f-5e597072aeee@nvidia.com>
On Thu, Oct 31, 2019 at 10:28:12AM -0700, Ralph Campbell wrote:
> > > > > > It seems especially over-complicated to use a full page table layout
> > > > > > for this, wouldn't something simple like an xarray be good enough for
> > > > > > test purposes?
> > > > >
> > > > > Possibly. A page table is really just a lookup table from virtual address
> > > > > to pfn/page. Part of the rationale was to mimic what a real device
> > > > > might do.
> > > >
> > > > Well, but the details of the page table layout don't see really
> > > > important to this testing, IMHO.
> > >
> > > One problem with XArray is that on 32-bit machines the value would
> > > need to be u64 to hold a pfn which won't fit in a ULONG_MAX.
> > > I guess we could make the driver 64-bit only.
> >
> > Why would a 32 bit machine need a 64 bit pfn?
> >
>
> On x86, Physical Address Extension (PAE) uses a 64 bit PTE.
> See arch/x86/include/asm/pgtable_32_types.h which includes
> arch/x86/include/asm/pgtable-3level_types.h.
That is the content of the PTE, not the address of the PTE. In this
case the xarray index is the 'virtual' address of the fictional device
and it can easily be 32 bits with no problem
Jason
next prev parent reply other threads:[~2019-10-31 17:34 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-23 19:55 [PATCH v3 0/3] HMM tests and minor fixes Ralph Campbell
2019-10-23 19:55 ` [PATCH v3 1/3] mm/hmm: make full use of walk_page_range() Ralph Campbell
2019-10-29 17:40 ` Jason Gunthorpe
2019-10-23 19:55 ` [PATCH v3 2/3] mm/hmm: allow snapshot of the special zero page Ralph Campbell
2019-10-23 20:27 ` Jerome Glisse
2019-10-24 9:27 ` David Hildenbrand
2019-10-29 17:27 ` Jason Gunthorpe
2019-10-23 19:55 ` [PATCH v3 3/3] mm/hmm/test: add self tests for HMM Ralph Campbell
2019-10-23 20:28 ` Jerome Glisse
2019-10-23 21:55 ` Ralph Campbell
2019-10-29 17:58 ` Jason Gunthorpe
2019-10-29 21:16 ` Ralph Campbell
2019-10-29 23:12 ` Jason Gunthorpe
2019-10-31 0:14 ` Ralph Campbell
2019-10-31 12:42 ` Jason Gunthorpe
2019-10-31 17:28 ` Ralph Campbell
2019-10-31 17:34 ` Jason Gunthorpe [this message]
2019-10-31 17:48 ` Ralph Campbell
2019-10-30 18:34 ` Qian Cai
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