From: Ralph Campbell <rcampbell@nvidia.com>
To: Jason Gunthorpe <jgg@mellanox.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 10:48:18 -0700 [thread overview]
Message-ID: <8ed8f207-42be-8f86-1778-67fbd4f81370@nvidia.com> (raw)
In-Reply-To: <20191031173438.GL22766@mellanox.com>
On 10/31/19 10:34 AM, Jason Gunthorpe wrote:
> 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
>
Oh, I see. You mean use a 32-bit user virtual address for the index
and store a pointer to the 64-bit PTE which of course would be
32 bit. That should work.
I was stuck on thinking the PTE needed to be stored.
next prev parent reply other threads:[~2019-10-31 17:48 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
2019-10-31 17:48 ` Ralph Campbell [this message]
2019-10-30 18:34 ` Qian Cai
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