From: "Thomas Hellström (Intel)" <thomas_os@shipmail.org>
To: "Christian König" <christian.koenig@amd.com>,
"Jason Gunthorpe" <jgg@nvidia.com>
Cc: David Airlie <airlied@linux.ie>,
linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org,
linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [RFC PATCH 1/2] mm,drm/ttm: Block fast GUP to TTM huge pages
Date: Thu, 25 Mar 2021 14:31:20 +0100 [thread overview]
Message-ID: <9e924f37-c638-afc7-0354-7258836772b1@shipmail.org> (raw)
In-Reply-To: <fc548803-7e12-83d7-10b8-4774cae4747f@amd.com>
Hi,
On 3/25/21 2:02 PM, Christian König wrote:
>
>
> Am 25.03.21 um 13:36 schrieb Thomas Hellström (Intel):
>>
>> On 3/25/21 1:09 PM, Christian König wrote:
>>> Am 25.03.21 um 13:01 schrieb Jason Gunthorpe:
>>>> On Thu, Mar 25, 2021 at 12:53:15PM +0100, Thomas Hellström (Intel)
>>>> wrote:
>>>>
>>>>> Nope. The point here was that in this case, to make sure mmap uses
>>>>> the
>>>>> correct VA to give us a reasonable chance of alignement, the
>>>>> driver might
>>>>> need to be aware of and do trickery with the huge page-table-entry
>>>>> sizes
>>>>> anyway, although I think in most cases a standard helper for this
>>>>> can be
>>>>> supplied.
>>>> Of course the driver needs some way to influence the VA mmap uses,
>>>> gernally it should align to the natural page size of the device
>>>
>>> Well a mmap() needs to be aligned to the page size of the CPU, but
>>> not necessarily to the one of the device.
>>>
>>> So I'm pretty sure the device driver should not be involved in any
>>> way the choosing of the VA for the CPU mapping.
>>>
>>> Christian.
>>>
>> We've had this discussion before and at that time I managed to
>> convince you by pointing to the shmem helper for this,
>> shmem_get_umapped_area().
>
> No, you didn't convinced me. I was just surprised that this is
> something under driver control.
>
>>
>> Basically there are two ways to do this. Either use a standard helper
>> similar to shmem's, and then the driver needs to align physical
>> (device) huge page boundaries to address space offset huge page
>> boundaries. If you don't do that you can just as well use a custom
>> function that adjusts for you not doing that
>> (drm_get_unmapped_area()). Both require driver knowledge of the size
>> of huge pages.
>
> And once more, at least for GPU drivers that looks like the totally
> wrong approach to me.
>
> Aligning the VMA so that huge page allocations become possible is the
> job of the MM subsystem and not that of the drivers.
>
Previous discussion here
https://www.spinics.net/lists/linux-mm/msg205291.html
>>
>> Without a function to adjust, mmap will use it's default (16 byte?)
>> alignment and chance of alignment becomes very small.
>
> Well it's 4KiB at least.
Yes :/ ...
>
> Regards,
> Christian.
>
Thanks,
Thomas
next prev parent reply other threads:[~2021-03-25 13:31 UTC|newest]
Thread overview: 63+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-21 18:45 [RFC PATCH 0/2] mm,drm/ttm: Always block GUP to TTM pages Thomas Hellström (Intel)
2021-03-21 18:45 ` [RFC PATCH 1/2] mm,drm/ttm: Block fast GUP to TTM huge pages Thomas Hellström (Intel)
2021-03-23 11:34 ` Daniel Vetter
2021-03-23 16:34 ` Thomas Hellström (Intel)
2021-03-23 16:37 ` Jason Gunthorpe
2021-03-23 16:59 ` Christoph Hellwig
2021-03-23 17:06 ` Thomas Hellström (Intel)
2021-03-24 9:56 ` Daniel Vetter
2021-03-24 12:24 ` Jason Gunthorpe
2021-03-24 12:35 ` Thomas Hellström (Intel)
2021-03-24 12:41 ` Jason Gunthorpe
2021-03-24 13:35 ` Thomas Hellström (Intel)
2021-03-24 13:48 ` Jason Gunthorpe
2021-03-24 15:50 ` Thomas Hellström (Intel)
2021-03-24 16:38 ` Jason Gunthorpe
2021-03-24 18:31 ` Christian König
2021-03-24 20:07 ` Thomas Hellström (Intel)
2021-03-24 23:14 ` Jason Gunthorpe
2021-03-25 7:48 ` Thomas Hellström (Intel)
2021-03-25 8:27 ` Christian König
2021-03-25 9:51 ` Thomas Hellström (Intel)
2021-03-25 11:30 ` Jason Gunthorpe
2021-03-25 11:53 ` Thomas Hellström (Intel)
2021-03-25 12:01 ` Jason Gunthorpe
2021-03-25 12:09 ` Christian König
2021-03-25 12:36 ` Thomas Hellström (Intel)
2021-03-25 13:02 ` Christian König
2021-03-25 13:31 ` Thomas Hellström (Intel) [this message]
2021-03-25 12:42 ` Jason Gunthorpe
2021-03-25 13:05 ` Christian König
2021-03-25 13:17 ` Jason Gunthorpe
2021-03-25 13:26 ` Christian König
2021-03-25 13:33 ` Jason Gunthorpe
2021-03-25 13:54 ` Christian König
2021-03-25 13:56 ` Jason Gunthorpe
2021-03-25 7:49 ` Christian König
2021-03-25 9:41 ` Daniel Vetter
2021-03-23 13:52 ` Jason Gunthorpe
2021-03-23 15:05 ` Thomas Hellström (Intel)
2021-03-23 19:52 ` Williams, Dan J
2021-03-23 20:42 ` Thomas Hellström (Intel)
2021-03-24 9:58 ` Daniel Vetter
2021-03-24 10:05 ` Thomas Hellström (Intel)
[not found] ` <75423f64-adef-a2c4-8e7d-2cb814127b18@intel.com>
2021-03-24 20:22 ` Thomas Hellström (Intel)
2021-03-24 20:25 ` Dave Hansen
2021-03-25 17:51 ` Thomas Hellström (Intel)
2021-03-25 17:55 ` Jason Gunthorpe
2021-03-25 18:13 ` Thomas Hellström (Intel)
2021-03-25 18:24 ` Jason Gunthorpe
2021-03-25 18:42 ` Thomas Hellström (Intel)
2021-03-26 9:08 ` Thomas Hellström (Intel)
2021-03-26 11:46 ` Jason Gunthorpe
2021-03-26 12:33 ` Thomas Hellström (Intel)
2021-03-21 18:45 ` [RFC PATCH 2/2] mm,drm/ttm: Use VM_PFNMAP for TTM vmas Thomas Hellström (Intel)
2021-03-22 7:47 ` Christian König
2021-03-22 8:13 ` Thomas Hellström (Intel)
2021-03-23 11:57 ` Christian König
2021-03-23 11:47 ` Daniel Vetter
2021-03-23 14:04 ` Jason Gunthorpe
2021-03-23 15:51 ` Thomas Hellström (Intel)
2021-03-23 14:00 ` Jason Gunthorpe
2021-03-23 15:46 ` Thomas Hellström (Intel)
2021-03-23 16:06 ` Jason Gunthorpe
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