Re: [PATCH] drm/ttm: remove ttm_bo_wait_unreserved

From: "Thomas Hellström (VMware)" <thomas_os@shipmail.org>
To: "Koenig, Christian" <Christian.Koenig@amd.com>,
	Daniel Vetter <daniel@ffwll.ch>
Cc: Thomas Hellstrom <thellstrom@vmware.com>,
	Daniel Vetter <daniel.vetter@ffwll.ch>,
	Intel Graphics Development <intel-gfx@lists.freedesktop.org>,
	DRI Development <dri-devel@lists.freedesktop.org>,
	"Huang, Ray" <Ray.Huang@amd.com>,
	VMware Graphics <linux-graphics-maintainer@vmware.com>,
	Gerd Hoffmann <kraxel@redhat.com>,
	Daniel Vetter <daniel.vetter@intel.com>
Subject: Re: [PATCH] drm/ttm: remove ttm_bo_wait_unreserved
Date: Thu, 22 Aug 2019 16:30:19 +0200	[thread overview]
Message-ID: <13618321-f250-f46d-1ad8-c638f9c0f9e7@shipmail.org> (raw)
In-Reply-To: <dbf459df-e22a-7b20-6413-37cfa70c22cf@shipmail.org>

On 8/22/19 4:24 PM, Thomas Hellström (VMware) wrote:
> On 8/22/19 4:02 PM, Koenig, Christian wrote:
>> Am 22.08.19 um 15:06 schrieb Daniel Vetter:
>>> On Thu, Aug 22, 2019 at 07:56:56AM +0000, Koenig, Christian wrote:
>>>> Am 22.08.19 um 08:49 schrieb Daniel Vetter:
>>>>> With nouveau fixed all ttm-using drives have the correct nesting of
>>>>> mmap_sem vs dma_resv, and we can just lock the buffer.
>>>>>
>>>>> Assuming I didn't screw up anything with my audit of course.
>>>>>
>>>>> v2:
>>>>> - Dont forget wu_mutex (Christian König)
>>>>> - Keep the mmap_sem-less wait optimization (Thomas)
>>>>> - Use _lock_interruptible to be good citizens (Thomas)
>>>>>
>>>>> Reviewed-by: Christian König <christian.koenig@amd.com>
>>> btw I realized I didn't remove your r-b, since v1 was broken.
>>>
>>> For formality, can you pls reaffirm, or still something broken?
>> My r-b is still valid.
>>
>> Only problem I see is that neither of us seems to have a good idea about
>> the different VM_FAULT_* replies.
>
> I took a look in mm/gup.c. It seems like when using get_user_pages, 
> VM_FAULT_RETRY will retry 

s/retry/return/


> to a requesting caller telling it that a long wait was expected and 
> not performed, whereas VM_FAULT_NOPAGE will just keep get_user_pages 
> to spin. So the proposed patch should be correct from my understanding.
>
> If the fault originates from user-space, I guess either is fine.
>
> /Thomas

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