From: Ralph Campbell <rcampbell@nvidia.com>
To: Jason Gunthorpe <jgg@mellanox.com>
Cc: Christoph Hellwig <hch@lst.de>,
Andrew Morton <akpm@linux-foundation.org>,
Jerome Glisse <jglisse@redhat.com>,
John Hubbard <jhubbard@nvidia.com>, Shuah Khan <shuah@kernel.org>,
"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>,
"linux-kselftest@vger.kernel.org"
<linux-kselftest@vger.kernel.org>
Subject: Re: [PATCH v4 2/2] mm/hmm/test: add self tests for HMM
Date: Mon, 18 Nov 2019 10:32:18 -0800 [thread overview]
Message-ID: <912f9f23-fa2a-1dd7-3f91-f7175094c2e2@nvidia.com> (raw)
In-Reply-To: <20191115140619.GC3873@mellanox.com>
On 11/15/19 6:06 AM, Jason Gunthorpe wrote:
> On Thu, Nov 14, 2019 at 03:06:05PM -0800, Ralph Campbell wrote:
>>
>> On 11/13/19 5:51 AM, Christoph Hellwig wrote:
>>> On Tue, Nov 12, 2019 at 11:45:52PM +0000, Jason Gunthorpe wrote:
>>>>> Well, it would mean registering for the whole process address space.
>>>>> I'll give it a try.
>>>>
>>>> I'm not sure it makes much sense that this testing is essentially
>>>> modeled after nouveau's usage which is very strange compared to the
>>>> other drivers.
>>>
>>> Which means we really should make the test cases fit the proper usage.
>>> Maybe defer the tests for 5.5 and just merge the first patch for now?
>>>
>>
>> I think this a good point to discuss.
>> Some devices will want to register for all changes to the process address
>> space because there is no requirement to preregister regions that the
>> device can access verses devices like InfiniBand where a range of addresses
>> have to be registered before the device can access those addresses.
>
> But this is a very bad idea to register and do HW actions for ranges
> that can't possibly have any pages registered. It slows down the
> entire application
>
> I think the ODP approach might be saner, when it mirrors the entire
> address space it chops it up into VA chunks, and once a page is
> registered on the HW the VA chunk goes into the interval tree.
>
> Presumably the GPU also has some kind of page table tree and you could
> set one of the levels as the VA interval when there are populated children
>
> Jason
I wasn't suggesting that HW invalidates happen in two places.
I'm suggesting the two styles of invalidates can work together.
For example, what if a driver calls mmu_notifier_register(mn, mm)
to register for address space wide invalidations, then some time
later there is a device page table fault and the driver calls
mmu_range_notifier_insert() but with a NULL ops.invalidate.
The fault handler follows the nouveau/test_hmm pattern to call
mmu_range_read_begin()
hmm_range_fault()
device lock
mmu_range_read_retry()
update device page tables
device unlock
mmu_range_notifier_remove()
The global invalidate() callback would get the device lock and
call into mm to update the sequence number of any affected ranges
instead of having a range invalidate callback, and then do the HW
invalidations.
next prev parent reply other threads:[~2019-11-18 18:32 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-04 22:21 [PATCH v4 0/2] HMM tests and minor fixes Ralph Campbell
2019-11-04 22:21 ` [PATCH v4 1/2] mm/hmm: make full use of walk_page_range() Ralph Campbell
2019-11-12 15:18 ` Christoph Hellwig
2019-11-12 22:21 ` Ralph Campbell
2019-11-14 14:24 ` Jason Gunthorpe
2019-11-04 22:21 ` [PATCH v4 2/2] mm/hmm/test: add self tests for HMM Ralph Campbell
2019-11-12 15:25 ` Christoph Hellwig
2019-11-12 21:51 ` Ralph Campbell
2019-11-12 23:45 ` Jason Gunthorpe
2019-11-13 13:51 ` Christoph Hellwig
2019-11-14 23:06 ` Ralph Campbell
2019-11-15 14:06 ` Jason Gunthorpe
2019-11-18 18:32 ` Ralph Campbell [this message]
2019-11-18 18:42 ` Jason Gunthorpe
2019-11-13 0:08 ` Andrew Morton
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