From: "Christian König" <ckoenig.leichtzumerken@gmail.com>
To: "Andrey Grodzovsky" <Andrey.Grodzovsky@amd.com>,
"Daniel Vetter" <daniel.vetter@ffwll.ch>,
"Christian König" <christian.koenig@amd.com>
Cc: "Alex Deucher" <alexdeucher@gmail.com>,
"Michel Dänzer" <michel@daenzer.net>,
"amd-gfx list" <amd-gfx@lists.freedesktop.org>,
"Pekka Paalanen" <ppaalanen@gmail.com>,
dri-devel <dri-devel@lists.freedesktop.org>
Subject: Re: [PATCH v2 1/8] drm: Add dummy page per device or GEM object
Date: Sat, 14 Nov 2020 09:41:03 +0100 [thread overview]
Message-ID: <fefd0ae2-7776-0e57-cc97-805f6237c82f@gmail.com> (raw)
In-Reply-To: <a13a7893-a3dd-c4f6-0a0f-0fce8c005e53@amd.com>
Am 13.11.20 um 21:52 schrieb Andrey Grodzovsky:
>
> On 6/22/20 1:50 PM, Daniel Vetter wrote:
>> On Mon, Jun 22, 2020 at 7:45 PM Christian König
>> <christian.koenig@amd.com> wrote:
>>> Am 22.06.20 um 16:32 schrieb Andrey Grodzovsky:
>>>> On 6/22/20 9:18 AM, Christian König wrote:
>>>>> Am 21.06.20 um 08:03 schrieb Andrey Grodzovsky:
>>>>>> Will be used to reroute CPU mapped BO's page faults once
>>>>>> device is removed.
>>>>>>
>>>>>> Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
>>>>>> ---
>>>>>> drivers/gpu/drm/drm_file.c | 8 ++++++++
>>>>>> drivers/gpu/drm/drm_prime.c | 10 ++++++++++
>>>>>> include/drm/drm_file.h | 2 ++
>>>>>> include/drm/drm_gem.h | 2 ++
>>>>>> 4 files changed, 22 insertions(+)
>>>>>>
>>>>>> diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c
>>>>>> index c4c704e..67c0770 100644
>>>>>> --- a/drivers/gpu/drm/drm_file.c
>>>>>> +++ b/drivers/gpu/drm/drm_file.c
>>>>>> @@ -188,6 +188,12 @@ struct drm_file *drm_file_alloc(struct
>>>>>> drm_minor *minor)
>>>>>> goto out_prime_destroy;
>>>>>> }
>>>>>> + file->dummy_page = alloc_page(GFP_KERNEL | __GFP_ZERO);
>>>>>> + if (!file->dummy_page) {
>>>>>> + ret = -ENOMEM;
>>>>>> + goto out_prime_destroy;
>>>>>> + }
>>>>>> +
>>>>>> return file;
>>>>>> out_prime_destroy:
>>>>>> @@ -284,6 +290,8 @@ void drm_file_free(struct drm_file *file)
>>>>>> if (dev->driver->postclose)
>>>>>> dev->driver->postclose(dev, file);
>>>>>> + __free_page(file->dummy_page);
>>>>>> +
>>>>>> drm_prime_destroy_file_private(&file->prime);
>>>>>> WARN_ON(!list_empty(&file->event_list));
>>>>>> diff --git a/drivers/gpu/drm/drm_prime.c
>>>>>> b/drivers/gpu/drm/drm_prime.c
>>>>>> index 1de2cde..c482e9c 100644
>>>>>> --- a/drivers/gpu/drm/drm_prime.c
>>>>>> +++ b/drivers/gpu/drm/drm_prime.c
>>>>>> @@ -335,6 +335,13 @@ int drm_gem_prime_fd_to_handle(struct
>>>>>> drm_device *dev,
>>>>>> ret = drm_prime_add_buf_handle(&file_priv->prime,
>>>>>> dma_buf, *handle);
>>>>>> +
>>>>>> + if (!ret) {
>>>>>> + obj->dummy_page = alloc_page(GFP_KERNEL | __GFP_ZERO);
>>>>>> + if (!obj->dummy_page)
>>>>>> + ret = -ENOMEM;
>>>>>> + }
>>>>>> +
>>>>> While the per file case still looks acceptable this is a clear NAK
>>>>> since it will massively increase the memory needed for a prime
>>>>> exported object.
>>>>>
>>>>> I think that this is quite overkill in the first place and for the
>>>>> hot unplug case we can just use the global dummy page as well.
>>>>>
>>>>> Christian.
>>>>
>>>> Global dummy page is good for read access, what do you do on write
>>>> access ? My first approach was indeed to map at first global dummy
>>>> page as read only and mark the vma->vm_flags as !VM_SHARED assuming
>>>> that this would trigger Copy On Write flow in core mm
>>>> (https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Felixir.bootlin.com%2Flinux%2Fv5.7-rc7%2Fsource%2Fmm%2Fmemory.c%23L3977&data=02%7C01%7CAndrey.Grodzovsky%40amd.com%7C3753451d037544e7495408d816d4c4ee%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637284450384586120&sdata=ZpRaQgqA5K4jRfidOiedey0AleeYQ97WNUkGA29ERA0%3D&reserved=0)
>>>>
>>>> on the next page fault to same address triggered by a write access but
>>>> then i realized a new COW page will be allocated for each such mapping
>>>> and this is much more wasteful then having a dedicated page per GEM
>>>> object.
>>> Yeah, but this is only for a very very small corner cases. What we need
>>> to prevent is increasing the memory usage during normal operation to
>>> much.
>>>
>>> Using memory during the unplug is completely unproblematic because we
>>> just released quite a bunch of it by releasing all those system memory
>>> buffers.
>>>
>>> And I'm pretty sure that COWed pages are correctly accounted towards
>>> the
>>> used memory of a process.
>>>
>>> So I think if that approach works as intended and the COW pages are
>>> released again on unmapping it would be the perfect solution to the
>>> problem.
>>>
>>> Daniel what do you think?
>> If COW works, sure sounds reasonable. And if we can make sure we
>> managed to drop all the system allocations (otherwise suddenly 2x
>> memory usage, worst case). But I have no idea whether we can
>> retroshoehorn that into an established vma, you might have fun stuff
>> like a mkwrite handler there (which I thought is the COW handler
>> thing, but really no idea).
>>
>> If we need to massively change stuff then I think rw dummy page,
>> allocated on first fault after hotunplug (maybe just make it one per
>> object, that's simplest) seems like the much safer option. Much less
>> code that can go wrong.
>> -Daniel
>
>
> Regarding COW, i was looking into how to properly implement it from
> within the fault handler (i.e. ttm_bo_vm_fault)
> and the main obstacle I hit is that of exclusive access to the
> vm_area_struct, i need to be able to modify
> vma->vm_flags (and vm_page_prot) to remove VM_SHARED bit so COW can
> be triggered on subsequent write access
> fault (here
> https://elixir.bootlin.com/linux/latest/source/mm/memory.c#L4128)
> but core mm takes only read side mm_sem (here for example
> https://elixir.bootlin.com/linux/latest/source/drivers/iommu/amd/iommu_v2.c#L488)
> and so I am not supposed to modify vm_area_struct in this case. I am
> not sure if it's legit to write lock tthe mm_sem from this point.
> I found some discussions about this here
> http://lkml.iu.edu/hypermail/linux/kernel/1909.1/02754.html but it
> wasn't really clear to me
> what's the solution.
>
> In any case, seems to me that easier and more memory saving solution
> would be to just switch to per ttm bo dumy rw page that
> would be allocated on demand as you suggested here. This should also
> take care of imported BOs and flink cases.
> Then i can drop the per device FD and per GEM object FD dummy BO and
> the ugly loop i am using in patch 2 to match faulting BO to the right
> dummy page.
>
> Does this makes sense ?
I still don't see the information leak as much of a problem, but if
Daniel insists we should probably do this.
But could we at least have only one page per client instead of per BO?
Thanks,
Christian.
>
> Andrey
>
>
>>
>>> Regards,
>>> Christian.
>>>
>>>> We can indeed optimize by allocating this dummy page on the first page
>>>> fault after device disconnect instead on GEM object creation.
>>>>
>>>> Andrey
>>>>
>>>>
>>>>>> mutex_unlock(&file_priv->prime.lock);
>>>>>> if (ret)
>>>>>> goto fail;
>>>>>> @@ -1006,6 +1013,9 @@ void drm_prime_gem_destroy(struct
>>>>>> drm_gem_object *obj, struct sg_table *sg)
>>>>>> dma_buf_unmap_attachment(attach, sg, DMA_BIDIRECTIONAL);
>>>>>> dma_buf = attach->dmabuf;
>>>>>> dma_buf_detach(attach->dmabuf, attach);
>>>>>> +
>>>>>> + __free_page(obj->dummy_page);
>>>>>> +
>>>>>> /* remove the reference */
>>>>>> dma_buf_put(dma_buf);
>>>>>> }
>>>>>> diff --git a/include/drm/drm_file.h b/include/drm/drm_file.h
>>>>>> index 19df802..349a658 100644
>>>>>> --- a/include/drm/drm_file.h
>>>>>> +++ b/include/drm/drm_file.h
>>>>>> @@ -335,6 +335,8 @@ struct drm_file {
>>>>>> */
>>>>>> struct drm_prime_file_private prime;
>>>>>> + struct page *dummy_page;
>>>>>> +
>>>>>> /* private: */
>>>>>> #if IS_ENABLED(CONFIG_DRM_LEGACY)
>>>>>> unsigned long lock_count; /* DRI1 legacy lock count */
>>>>>> diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h
>>>>>> index 0b37506..47460d1 100644
>>>>>> --- a/include/drm/drm_gem.h
>>>>>> +++ b/include/drm/drm_gem.h
>>>>>> @@ -310,6 +310,8 @@ struct drm_gem_object {
>>>>>> *
>>>>>> */
>>>>>> const struct drm_gem_object_funcs *funcs;
>>>>>> +
>>>>>> + struct page *dummy_page;
>>>>>> };
>>>>>> /**
>>
> _______________________________________________
> amd-gfx mailing list
> amd-gfx@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/amd-gfx
_______________________________________________
amd-gfx mailing list
amd-gfx@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/amd-gfx
next prev parent reply other threads:[~2020-11-14 8:41 UTC|newest]
Thread overview: 97+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-21 6:03 [PATCH v2 0/8] RFC Support hot device unplug in amdgpu Andrey Grodzovsky
2020-06-21 6:03 ` [PATCH v2 1/8] drm: Add dummy page per device or GEM object Andrey Grodzovsky
2020-06-22 9:35 ` Daniel Vetter
2020-06-22 14:21 ` Pekka Paalanen
2020-06-22 14:24 ` Daniel Vetter
2020-06-22 14:28 ` Pekka Paalanen
2020-11-09 20:34 ` Andrey Grodzovsky
2020-11-15 6:39 ` Andrey Grodzovsky
2020-06-22 13:18 ` Christian König
2020-06-22 14:23 ` Daniel Vetter
2020-06-22 14:32 ` Andrey Grodzovsky
2020-06-22 17:45 ` Christian König
2020-06-22 17:50 ` Daniel Vetter
2020-11-09 20:53 ` Andrey Grodzovsky
2020-11-13 20:52 ` Andrey Grodzovsky
2020-11-14 8:41 ` Christian König [this message]
2020-11-14 9:51 ` Daniel Vetter
2020-11-14 9:57 ` Daniel Vetter
2020-11-16 9:42 ` Michel Dänzer
2020-11-15 6:34 ` Andrey Grodzovsky
2020-11-16 9:48 ` Christian König
2020-11-16 19:00 ` Andrey Grodzovsky
2020-11-16 20:36 ` Christian König
2020-11-16 20:42 ` Andrey Grodzovsky
2020-11-19 10:01 ` Christian König
2020-06-21 6:03 ` [PATCH v2 2/8] drm/ttm: Remap all page faults to per process dummy page Andrey Grodzovsky
2020-06-22 9:41 ` Daniel Vetter
2020-06-24 3:31 ` Andrey Grodzovsky
2020-06-24 7:19 ` Daniel Vetter
2020-11-10 17:41 ` Andrey Grodzovsky
2020-06-22 19:30 ` Christian König
2020-06-21 6:03 ` [PATCH v2 3/8] drm/ttm: Add unampping of the entire device address space Andrey Grodzovsky
2020-06-22 9:45 ` Daniel Vetter
2020-06-23 5:00 ` Andrey Grodzovsky
2020-06-23 10:25 ` Daniel Vetter
2020-06-23 12:55 ` Christian König
2020-06-22 19:37 ` Christian König
2020-06-22 19:47 ` Alex Deucher
2020-06-21 6:03 ` [PATCH v2 4/8] drm/amdgpu: Split amdgpu_device_fini into early and late Andrey Grodzovsky
2020-06-22 9:48 ` Daniel Vetter
2020-11-12 4:19 ` Andrey Grodzovsky
2020-11-12 9:29 ` Daniel Vetter
2020-06-21 6:03 ` [PATCH v2 5/8] drm/amdgpu: Refactor sysfs removal Andrey Grodzovsky
2020-06-22 9:51 ` Daniel Vetter
2020-06-22 11:21 ` Greg KH
2020-06-22 16:07 ` Andrey Grodzovsky
2020-06-22 16:45 ` Greg KH
2020-06-23 4:51 ` Andrey Grodzovsky
2020-06-23 6:05 ` Greg KH
2020-06-24 3:04 ` Andrey Grodzovsky
2020-06-24 6:11 ` Greg KH
2020-06-25 1:52 ` Andrey Grodzovsky
2020-11-10 17:54 ` Andrey Grodzovsky
2020-11-10 17:59 ` Greg KH
2020-11-11 15:13 ` Andrey Grodzovsky
2020-11-11 15:34 ` Greg KH
2020-11-11 15:45 ` Andrey Grodzovsky
2020-11-11 16:06 ` Greg KH
2020-11-11 16:34 ` Andrey Grodzovsky
2020-12-02 15:48 ` Andrey Grodzovsky
2020-12-02 17:34 ` Greg KH
2020-12-02 18:02 ` Andrey Grodzovsky
2020-12-02 18:20 ` Greg KH
2020-12-02 18:40 ` Andrey Grodzovsky
2020-06-22 13:19 ` Christian König
2020-06-21 6:03 ` [PATCH v2 6/8] drm/amdgpu: Unmap entire device address space on device remove Andrey Grodzovsky
2020-06-22 9:56 ` Daniel Vetter
2020-06-22 19:38 ` Christian König
2020-06-22 19:48 ` Alex Deucher
2020-06-23 10:22 ` Daniel Vetter
2020-06-23 13:16 ` Christian König
2020-06-24 3:12 ` Andrey Grodzovsky
2020-06-21 6:03 ` [PATCH v2 7/8] drm/amdgpu: Fix sdma code crash post device unplug Andrey Grodzovsky
2020-06-22 9:55 ` Daniel Vetter
2020-06-22 19:40 ` Christian König
2020-06-23 5:11 ` Andrey Grodzovsky
2020-06-23 7:14 ` Christian König
2020-06-21 6:03 ` [PATCH v2 8/8] drm/amdgpu: Prevent any job recoveries after device is unplugged Andrey Grodzovsky
2020-06-22 9:53 ` Daniel Vetter
2020-11-17 18:38 ` Andrey Grodzovsky
2020-11-17 18:52 ` Daniel Vetter
2020-11-17 19:18 ` Andrey Grodzovsky
2020-11-17 19:49 ` Daniel Vetter
2020-11-17 20:07 ` Andrey Grodzovsky
2020-11-18 7:39 ` Daniel Vetter
2020-11-18 12:01 ` Christian König
2020-11-18 15:43 ` Luben Tuikov
2020-11-18 16:20 ` Andrey Grodzovsky
2020-11-19 7:55 ` Christian König
2020-11-19 15:02 ` Andrey Grodzovsky
2020-11-19 15:29 ` Daniel Vetter
2020-11-19 21:24 ` Andrey Grodzovsky
2020-11-18 0:46 ` Luben Tuikov
2020-06-22 9:46 ` [PATCH v2 0/8] RFC Support hot device unplug in amdgpu Daniel Vetter
2020-06-23 5:14 ` Andrey Grodzovsky
2020-06-23 9:04 ` Michel Dänzer
2020-06-24 3:21 ` Andrey Grodzovsky
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=fefd0ae2-7776-0e57-cc97-805f6237c82f@gmail.com \
--to=ckoenig.leichtzumerken@gmail.com \
--cc=Andrey.Grodzovsky@amd.com \
--cc=alexdeucher@gmail.com \
--cc=amd-gfx@lists.freedesktop.org \
--cc=christian.koenig@amd.com \
--cc=daniel.vetter@ffwll.ch \
--cc=dri-devel@lists.freedesktop.org \
--cc=michel@daenzer.net \
--cc=ppaalanen@gmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).