[v2,1/2] drm/ttm: Only allocate huge pages with new flag TTM_PAGE_FLAG_TRANSHUGE
diff mbox

Message ID 20180427130811.7642-1-michel@daenzer.net
State New
Headers show

Commit Message

Michel Dänzer April 27, 2018, 1:08 p.m. UTC
From: Michel Dänzer <michel.daenzer@amd.com>

Previously, TTM would always (with CONFIG_TRANSPARENT_HUGEPAGE enabled)
try to allocate huge pages. However, not all drivers can take advantage
of huge pages, but they would incur the overhead for allocating and
freeing them anyway.

Now, drivers which can take advantage of huge pages need to set the new
flag TTM_PAGE_FLAG_TRANSHUGE to get them. Drivers not setting this flag
no longer incur any overhead for allocating or freeing huge pages.

v2:
* Also guard swapping of consecutive pages in ttm_get_pages
* Reword commit log, hopefully clearer now

Cc: stable@vger.kernel.org
Signed-off-by: Michel Dänzer <michel.daenzer@amd.com>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c  |  2 +-
 drivers/gpu/drm/ttm/ttm_page_alloc.c     | 35 +++++++++++++++++-------
 drivers/gpu/drm/ttm/ttm_page_alloc_dma.c |  8 ++++--
 include/drm/ttm/ttm_tt.h                 |  1 +
 4 files changed, 32 insertions(+), 14 deletions(-)

Comments

Ilia Mirkin April 28, 2018, 4:30 p.m. UTC | #1
On Fri, Apr 27, 2018 at 9:08 AM, Michel Dänzer <michel@daenzer.net> wrote:
> From: Michel Dänzer <michel.daenzer@amd.com>
>
> Previously, TTM would always (with CONFIG_TRANSPARENT_HUGEPAGE enabled)
> try to allocate huge pages. However, not all drivers can take advantage
> of huge pages, but they would incur the overhead for allocating and
> freeing them anyway.
>
> Now, drivers which can take advantage of huge pages need to set the new
> flag TTM_PAGE_FLAG_TRANSHUGE to get them. Drivers not setting this flag
> no longer incur any overhead for allocating or freeing huge pages.
>
> v2:
> * Also guard swapping of consecutive pages in ttm_get_pages
> * Reword commit log, hopefully clearer now
>
> Cc: stable@vger.kernel.org
> Signed-off-by: Michel Dänzer <michel.daenzer@amd.com>

Both I and lots of other people, based on reports, are still seeing
plenty of issues with this as late as 4.16.4. Admittedly I'm on
nouveau, but others have reported issues with radeon/amdgpu as well.
It's been going on since the feature was merged in v4.15, with what
seems like little investigation from the authors introducing the
feature.

We now have *two* broken releases, v4.15 and v4.16 (anything that
spews error messages and stack traces ad-infinitum in dmesg is, by
definition, broken). You're putting this behind a flag now (finally),
but should it be enabled anywhere? Why is it being flipped on for
amdgpu by default, despite the still-existing problems?

Reverting this feature without just resetting back to the code in
v4.14 is painful, but why make Joe User suffer by enabling it while
you're still working out the kinks?

  -ilia
Michel Dänzer April 28, 2018, 11:02 p.m. UTC | #2
On 2018-04-28 06:30 PM, Ilia Mirkin wrote:
> On Fri, Apr 27, 2018 at 9:08 AM, Michel Dänzer <michel@daenzer.net> wrote:
>> From: Michel Dänzer <michel.daenzer@amd.com>
>>
>> Previously, TTM would always (with CONFIG_TRANSPARENT_HUGEPAGE enabled)
>> try to allocate huge pages. However, not all drivers can take advantage
>> of huge pages, but they would incur the overhead for allocating and
>> freeing them anyway.
>>
>> Now, drivers which can take advantage of huge pages need to set the new
>> flag TTM_PAGE_FLAG_TRANSHUGE to get them. Drivers not setting this flag
>> no longer incur any overhead for allocating or freeing huge pages.
>>
>> v2:
>> * Also guard swapping of consecutive pages in ttm_get_pages
>> * Reword commit log, hopefully clearer now
>>
>> Cc: stable@vger.kernel.org
>> Signed-off-by: Michel Dänzer <michel.daenzer@amd.com>
> 
> Both I and lots of other people, based on reports, are still seeing
> plenty of issues with this as late as 4.16.4.

"lots of other people", "plenty of issues" sounds a bit exaggerated from
what I've seen. FWIW, while I did see the original messages myself, I
haven't seen any since Christian's original fix (see below), neither
with amdgpu nor radeon, even before this patch you followed up to.


> Admittedly I'm on nouveau, but others have reported issues with
> radeon/amdgpu as well. It's been going on since the feature was merged
> in v4.15, with what seems like little investigation from the authors
> introducing the feature.

That's not a fair assessment. See
https://bugs.freedesktop.org/show_bug.cgi?id=104082#c40 and following
comments.

Christian fixed the original issue in
d0bc0c2a31c95002d37c3cc511ffdcab851b3256 "swiotlb: suppress warning when
__GFP_NOWARN is set". Christian did his best to try and get the fix in
before 4.15 final, but for reasons beyond his control, it was delayed
until 4.16-rc1 and then backported to 4.15.5.

Unfortunately, there was an swiotlb regression (not directly related to
Christian's work) shortly after this fix, also in 4.16-rc1, which is now
fixed in 4.17-rc1 and will be backported to 4.16.y.

It looks like there's at least one more bug left, but it's not clear yet
when that was introduced, whether it's directly related to Christian's
work, or indeed what the impact is. Let's not get ahead of ourselves.


> We now have *two* broken releases, v4.15 and v4.16 (anything that
> spews error messages and stack traces ad-infinitum in dmesg is, by
> definition, broken).

I haven't seen any evidence that there's still an issue in 4.15, is
there any?


> You're putting this behind a flag now (finally),

I wrote this patch because I realized due to some remark I happened to
see you make this week on IRC that the huge page support in TTM was
enabled for all drivers. Instead of making that kind of remark on IRC,
it would have been more constructive, and more conducive to quick
implementation, to suggest making the feature not active for drivers
which don't need it in a mailing list post.


At least, please do more research before making this kind of negative
post.

P.S. You might also want to look into whether nouveau really should be
hitting swiotlb in these cases.
Ilia Mirkin April 28, 2018, 11:56 p.m. UTC | #3
On Sat, Apr 28, 2018 at 7:02 PM, Michel Dänzer <michel@daenzer.net> wrote:
> On 2018-04-28 06:30 PM, Ilia Mirkin wrote:
>> On Fri, Apr 27, 2018 at 9:08 AM, Michel Dänzer <michel@daenzer.net> wrote:
>>> From: Michel Dänzer <michel.daenzer@amd.com>
>>>
>>> Previously, TTM would always (with CONFIG_TRANSPARENT_HUGEPAGE enabled)
>>> try to allocate huge pages. However, not all drivers can take advantage
>>> of huge pages, but they would incur the overhead for allocating and
>>> freeing them anyway.
>>>
>>> Now, drivers which can take advantage of huge pages need to set the new
>>> flag TTM_PAGE_FLAG_TRANSHUGE to get them. Drivers not setting this flag
>>> no longer incur any overhead for allocating or freeing huge pages.
>>>
>>> v2:
>>> * Also guard swapping of consecutive pages in ttm_get_pages
>>> * Reword commit log, hopefully clearer now
>>>
>>> Cc: stable@vger.kernel.org
>>> Signed-off-by: Michel Dänzer <michel.daenzer@amd.com>
>>
>> Both I and lots of other people, based on reports, are still seeing
>> plenty of issues with this as late as 4.16.4.
>
> "lots of other people", "plenty of issues" sounds a bit exaggerated from
> what I've seen. FWIW, while I did see the original messages myself, I
> haven't seen any since Christian's original fix (see below), neither
> with amdgpu nor radeon, even before this patch you followed up to.

Probably a half-dozen reports of it with nouveau, in addition to
another bunch of people talking about it on the bug you mention below,
along with email threads on dri-devel.

I figured I didn't have to raise my own since it was identical to the
others, and, I assumed, was being handled.

>> Admittedly I'm on nouveau, but others have reported issues with
>> radeon/amdgpu as well. It's been going on since the feature was merged
>> in v4.15, with what seems like little investigation from the authors
>> introducing the feature.
>
> That's not a fair assessment. See
> https://bugs.freedesktop.org/show_bug.cgi?id=104082#c40 and following
> comments.
>
> Christian fixed the original issue in
> d0bc0c2a31c95002d37c3cc511ffdcab851b3256 "swiotlb: suppress warning when
> __GFP_NOWARN is set". Christian did his best to try and get the fix in
> before 4.15 final, but for reasons beyond his control, it was delayed
> until 4.16-rc1 and then backported to 4.15.5.

In case it's unclear, let me state this explicitly -- I totally get
that despite best intentions, bugs get introduced. I do it myself.
What I'm having trouble with is the handling once the issue is
discovered.

>
> Unfortunately, there was an swiotlb regression (not directly related to
> Christian's work) shortly after this fix, also in 4.16-rc1, which is now
> fixed in 4.17-rc1 and will be backported to 4.16.y.

https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/commit/?h=v4.16.5&id=2c9dacf5bfe1e45d96dfe97cb71d2b717786a7b9

This guy? Didn't help. I'm running 4.16.4 right now.

> It looks like there's at least one more bug left, but it's not clear yet
> when that was introduced, whether it's directly related to Christian's
> work, or indeed what the impact is. Let's not get ahead of ourselves.

Whether it is directly related to that work or not, the issue
persists. There are two options:

 - When declaring things fixed, no serious attempt was actually made
at reproducing the underlying issues.
 - The authors truly can't reproduce the underlying issues users are
seeing and are taking stabs in the dark.

Given that a number of people are reporting problems, in either
scenario, the reasonable thing is to disable the feature, and figure
out what is going on. Maybe condition it on !CONFIG_SWIOTLB.

>> We now have *two* broken releases, v4.15 and v4.16 (anything that
>> spews error messages and stack traces ad-infinitum in dmesg is, by
>> definition, broken).
>
> I haven't seen any evidence that there's still an issue in 4.15, is
> there any?

Well, I did have a late 4.15 rc kernel in addition to the 'suppress
warning' patch. Now I'm questioning my memory of whether the issue was
resolved there or not. I'm pretty sure that 'not', but no longer 100%.
Either way, I think we all agree v4.15 was broken and more importantly
was *known* to be broken well in advance of the release. A reasonable
option would have been to disable the feature until the other bits
fell into place.

>> You're putting this behind a flag now (finally),
>
> I wrote this patch because I realized due to some remark I happened to
> see you make this week on IRC that the huge page support in TTM was
> enabled for all drivers. Instead of making that kind of remark on IRC,
> it would have been more constructive, and more conducive to quick
> implementation, to suggest making the feature not active for drivers
> which don't need it in a mailing list post.

I see IRC as a much faster and direct way of reaching the authors
and/or people who need to know an issue. As there was already a bug
filed about it and the issue was known about, I didn't really see a
reason to pile on (until now).

> At least, please do more research before making this kind of negative
> post.

Every time I've reported it, I've been told that patch X definitely
solves the issue. There was the original fix from Christian which went
into v4.15 and I'm pretty sure didn't fix it (I had it applied to a
4.15 tree), and then the later issue with the swiotlb logic inversion
bug which also didn't fix it. It's entirely possible that the true
issue lies not in the code that was written as part of this feature
enablement but rather existing code in handling of thp. But the end
result is that I have a broken kernel.

As a user who is not in a position to debug this directly due to lack
of time and knowledge, my options are limited. This issue hasn't
gotten a ton of visibility since it's waved away every time as
"fixed", so I'm trying to turn up the heat a little bit to cause a fix
or revert to happen. I believe the policy in Linux is "no
regressions", unlike many other graphics components where regressions
are welcome as long as they're downstream components of where the
change is made.

> P.S. You might also want to look into whether nouveau really should be
> hitting swiotlb in these cases.

I don't have a strong enough concept of what the swiotlb does and when
it's needed. Hopefully someone that does will take a look.

  -ilia
Koenig, Christian April 29, 2018, 7:02 a.m. UTC | #4
Am 29.04.2018 um 01:02 schrieb Michel Dänzer:
> On 2018-04-28 06:30 PM, Ilia Mirkin wrote:
>> On Fri, Apr 27, 2018 at 9:08 AM, Michel Dänzer <michel@daenzer.net> wrote:
>>> From: Michel Dänzer <michel.daenzer@amd.com>
>>>
>>> Previously, TTM would always (with CONFIG_TRANSPARENT_HUGEPAGE enabled)
>>> try to allocate huge pages. However, not all drivers can take advantage
>>> of huge pages, but they would incur the overhead for allocating and
>>> freeing them anyway.
>>>
>>> Now, drivers which can take advantage of huge pages need to set the new
>>> flag TTM_PAGE_FLAG_TRANSHUGE to get them. Drivers not setting this flag
>>> no longer incur any overhead for allocating or freeing huge pages.
>>>
>>> v2:
>>> * Also guard swapping of consecutive pages in ttm_get_pages
>>> * Reword commit log, hopefully clearer now
>>>
>>> Cc: stable@vger.kernel.org
>>> Signed-off-by: Michel Dänzer <michel.daenzer@amd.com>
>> Both I and lots of other people, based on reports, are still seeing
>> plenty of issues with this as late as 4.16.4.
> "lots of other people", "plenty of issues" sounds a bit exaggerated from
> what I've seen. FWIW, while I did see the original messages myself, I
> haven't seen any since Christian's original fix (see below), neither
> with amdgpu nor radeon, even before this patch you followed up to.
>
>
>> Admittedly I'm on nouveau, but others have reported issues with
>> radeon/amdgpu as well. It's been going on since the feature was merged
>> in v4.15, with what seems like little investigation from the authors
>> introducing the feature.
> That's not a fair assessment. See
> https://bugs.freedesktop.org/show_bug.cgi?id=104082#c40 and following
> comments.
>
> Christian fixed the original issue in
> d0bc0c2a31c95002d37c3cc511ffdcab851b3256 "swiotlb: suppress warning when
> __GFP_NOWARN is set". Christian did his best to try and get the fix in
> before 4.15 final, but for reasons beyond his control, it was delayed
> until 4.16-rc1 and then backported to 4.15.5.
>
> Unfortunately, there was an swiotlb regression (not directly related to
> Christian's work) shortly after this fix, also in 4.16-rc1, which is now
> fixed in 4.17-rc1 and will be backported to 4.16.y.

And that's exactly the reason why I intentionally kept this enabled for 
all users of the TTM DMA page pool and not put it behind a flag.

This change has surfaced quite a number of bugs in the swiotlb code 
which could have caused issues before. It's just that those code path 
where never exercised massively before.

Additional to that using huge pages is beneficial for the MM and CPU TLB 
(not implemented yet) even when the GPU driver can't make much use of it.

> It looks like there's at least one more bug left, but it's not clear yet
> when that was introduced, whether it's directly related to Christian's
> work, or indeed what the impact is. Let's not get ahead of ourselves.

Well my patches surfaced the problems, but the underlying issues where 
present even before those changes and I'm very well involved in fixing 
the underlying issues.

I even considered to just revert the huge page path for the DMA pool 
allocator, but it's just that the TTM patches seem to work exactly as 
they are intended. So that doesn't feel like doing the right thing here.

>> We now have *two* broken releases, v4.15 and v4.16 (anything that
>> spews error messages and stack traces ad-infinitum in dmesg is, by
>> definition, broken).
> I haven't seen any evidence that there's still an issue in 4.15, is
> there any?

Not that I know of, the fix was backported as far as I know.

>> You're putting this behind a flag now (finally),
> I wrote this patch because I realized due to some remark I happened to
> see you make this week on IRC that the huge page support in TTM was
> enabled for all drivers. Instead of making that kind of remark on IRC,
> it would have been more constructive, and more conducive to quick
> implementation, to suggest making the feature not active for drivers
> which don't need it in a mailing list post.

I have to admit that I'm lacking behind taking care of the amdgpu/radeon 
user space issues just because of more important stuff to do, but the 
issues affecting other drivers should be fixed by now.

BTW: The user space problems for amdgpu/radeon seems to come from either 
the DDX or Glamour.

For example try playing a video user firefox with Glamour enabled and 
take a look at how much memory we free/allocate.

It's multiple gigabytes for just a few seconds playback, that strongly 
indicates that we allocate/free a texture for each displayed frame which 
is quite far from optimal.

Regards,
Christian.

>
>
> At least, please do more research before making this kind of negative
> post.
>
> P.S. You might also want to look into whether nouveau really should be
> hitting swiotlb in these cases.
>
Michel Dänzer April 30, 2018, 4:33 p.m. UTC | #5
On 2018-04-29 09:02 AM, Christian König wrote:
> Am 29.04.2018 um 01:02 schrieb Michel Dänzer:
>> On 2018-04-28 06:30 PM, Ilia Mirkin wrote:
>>> On Fri, Apr 27, 2018 at 9:08 AM, Michel Dänzer <michel@daenzer.net>
>>> wrote:
>>>> From: Michel Dänzer <michel.daenzer@amd.com>
>>>>
>>>> Previously, TTM would always (with CONFIG_TRANSPARENT_HUGEPAGE enabled)
>>>> try to allocate huge pages. However, not all drivers can take advantage
>>>> of huge pages, but they would incur the overhead for allocating and
>>>> freeing them anyway.
>>>>
>>>> Now, drivers which can take advantage of huge pages need to set the new
>>>> flag TTM_PAGE_FLAG_TRANSHUGE to get them. Drivers not setting this flag
>>>> no longer incur any overhead for allocating or freeing huge pages.
>>>>
>>>> v2:
>>>> * Also guard swapping of consecutive pages in ttm_get_pages
>>>> * Reword commit log, hopefully clearer now
>>>>
>>>> Cc: stable@vger.kernel.org
>>>> Signed-off-by: Michel Dänzer <michel.daenzer@amd.com>
>>> Both I and lots of other people, based on reports, are still seeing
>>> plenty of issues with this as late as 4.16.4.
>> "lots of other people", "plenty of issues" sounds a bit exaggerated from
>> what I've seen. FWIW, while I did see the original messages myself, I
>> haven't seen any since Christian's original fix (see below), neither
>> with amdgpu nor radeon, even before this patch you followed up to.
>>
>>
>>> Admittedly I'm on nouveau, but others have reported issues with
>>> radeon/amdgpu as well. It's been going on since the feature was merged
>>> in v4.15, with what seems like little investigation from the authors
>>> introducing the feature.
>> That's not a fair assessment. See
>> https://bugs.freedesktop.org/show_bug.cgi?id=104082#c40 and following
>> comments.
>>
>> Christian fixed the original issue in
>> d0bc0c2a31c95002d37c3cc511ffdcab851b3256 "swiotlb: suppress warning when
>> __GFP_NOWARN is set". Christian did his best to try and get the fix in
>> before 4.15 final, but for reasons beyond his control, it was delayed
>> until 4.16-rc1 and then backported to 4.15.5.
>>
>> Unfortunately, there was an swiotlb regression (not directly related to
>> Christian's work) shortly after this fix, also in 4.16-rc1, which is now
>> fixed in 4.17-rc1 and will be backported to 4.16.y.
> 
> And that's exactly the reason why I intentionally kept this enabled for
> all users of the TTM DMA page pool and not put it behind a flag.
> 
> This change has surfaced quite a number of bugs in the swiotlb code
> which could have caused issues before. It's just that those code path
> where never exercised massively before.
> 
> Additional to that using huge pages is beneficial for the MM and CPU TLB
> (not implemented yet) even when the GPU driver can't make much use of it.

Do I understand correctly that you're against this patch?

AFAIU the only benefit of huge pages with a driver which doesn't take
advantage of them directly is "for the MM". Can you describe a bit more
what that benefit is exactly? Is it expected to outweigh the cost of
allocating / freeing huge pages?


>> It looks like there's at least one more bug left, but it's not clear yet
>> when that was introduced, whether it's directly related to Christian's
>> work, or indeed what the impact is. Let's not get ahead of ourselves.
> 
> Well my patches surfaced the problems, but the underlying issues where
> present even before those changes and I'm very well involved in fixing
> the underlying issues.
> 
> I even considered to just revert the huge page path for the DMA pool
> allocator, but it's just that the TTM patches seem to work exactly as
> they are intended. So that doesn't feel like doing the right thing here.

I agree. Has anyone reported this to the DMA/SWIOTLB developers?
Christian König April 30, 2018, 6:22 p.m. UTC | #6
Am 30.04.2018 um 18:33 schrieb Michel Dänzer:
> On 2018-04-29 09:02 AM, Christian König wrote:
>> Am 29.04.2018 um 01:02 schrieb Michel Dänzer:
>>> On 2018-04-28 06:30 PM, Ilia Mirkin wrote:
>>>> On Fri, Apr 27, 2018 at 9:08 AM, Michel Dänzer <michel@daenzer.net>
>>>> wrote:
>>>>> From: Michel Dänzer <michel.daenzer@amd.com>
>>>>>
>>>>> Previously, TTM would always (with CONFIG_TRANSPARENT_HUGEPAGE enabled)
>>>>> try to allocate huge pages. However, not all drivers can take advantage
>>>>> of huge pages, but they would incur the overhead for allocating and
>>>>> freeing them anyway.
>>>>>
>>>>> Now, drivers which can take advantage of huge pages need to set the new
>>>>> flag TTM_PAGE_FLAG_TRANSHUGE to get them. Drivers not setting this flag
>>>>> no longer incur any overhead for allocating or freeing huge pages.
>>>>>
>>>>> v2:
>>>>> * Also guard swapping of consecutive pages in ttm_get_pages
>>>>> * Reword commit log, hopefully clearer now
>>>>>
>>>>> Cc: stable@vger.kernel.org
>>>>> Signed-off-by: Michel Dänzer <michel.daenzer@amd.com>
>>>> Both I and lots of other people, based on reports, are still seeing
>>>> plenty of issues with this as late as 4.16.4.
>>> "lots of other people", "plenty of issues" sounds a bit exaggerated from
>>> what I've seen. FWIW, while I did see the original messages myself, I
>>> haven't seen any since Christian's original fix (see below), neither
>>> with amdgpu nor radeon, even before this patch you followed up to.
>>>
>>>
>>>> Admittedly I'm on nouveau, but others have reported issues with
>>>> radeon/amdgpu as well. It's been going on since the feature was merged
>>>> in v4.15, with what seems like little investigation from the authors
>>>> introducing the feature.
>>> That's not a fair assessment. See
>>> https://bugs.freedesktop.org/show_bug.cgi?id=104082#c40 and following
>>> comments.
>>>
>>> Christian fixed the original issue in
>>> d0bc0c2a31c95002d37c3cc511ffdcab851b3256 "swiotlb: suppress warning when
>>> __GFP_NOWARN is set". Christian did his best to try and get the fix in
>>> before 4.15 final, but for reasons beyond his control, it was delayed
>>> until 4.16-rc1 and then backported to 4.15.5.
>>>
>>> Unfortunately, there was an swiotlb regression (not directly related to
>>> Christian's work) shortly after this fix, also in 4.16-rc1, which is now
>>> fixed in 4.17-rc1 and will be backported to 4.16.y.
>> And that's exactly the reason why I intentionally kept this enabled for
>> all users of the TTM DMA page pool and not put it behind a flag.
>>
>> This change has surfaced quite a number of bugs in the swiotlb code
>> which could have caused issues before. It's just that those code path
>> where never exercised massively before.
>>
>> Additional to that using huge pages is beneficial for the MM and CPU TLB
>> (not implemented yet) even when the GPU driver can't make much use of it.
> Do I understand correctly that you're against this patch?

Not completely, I've considered adding that multiple times myself.

I'm just torn apart between keeping it enabled so that the underlying 
bugs gets fixed and disabling it for a better end user experience.

But in general I would opt out for a pool configuration option, not a 
per driver flag.

> AFAIU the only benefit of huge pages with a driver which doesn't take
> advantage of them directly is "for the MM". Can you describe a bit more
> what that benefit is exactly?

When transparent huge pages are in effect we should have more huge pages 
than small pages in the system allocator.

So by enforcing allocation of small pages we fragment the huge pages 
once more and give khugepaged quite a bunch of work todo to gather them 
together into huge pages again.

> Is it expected to outweigh the cost of allocating / freeing huge pages?

Yes, and actually quite well (at least in theory).

>>> It looks like there's at least one more bug left, but it's not clear yet
>>> when that was introduced, whether it's directly related to Christian's
>>> work, or indeed what the impact is. Let's not get ahead of ourselves.
>> Well my patches surfaced the problems, but the underlying issues where
>> present even before those changes and I'm very well involved in fixing
>> the underlying issues.
>>
>> I even considered to just revert the huge page path for the DMA pool
>> allocator, but it's just that the TTM patches seem to work exactly as
>> they are intended. So that doesn't feel like doing the right thing here.
> I agree. Has anyone reported this to the DMA/SWIOTLB developers?

Yes, I fixed the original false positive messages myself with the 
swiotlb maintainer and I was CCed in fixing the recent fallout from 
Chris changes as well.

Regards,
Christian.
Dave Airlie April 30, 2018, 11:15 p.m. UTC | #7
>
>
> Yes, I fixed the original false positive messages myself with the swiotlb
> maintainer and I was CCed in fixing the recent fallout from Chris changes as
> well.

So do we have a good summary of where this at now?

I'm getting reports on 4.16.4 still displaying these, what hammer do I
need to hit things with to get 4.16.x+1 to not do this?

Is there still outstanding issues upstream.

For future reference I think how this should have gone down is

a) AMD implement a public CI with igt tests for all of this
b) we get these patches pushed and debugged.

Though to be a bit more constructive, I think you should have said at
-rc6 or 7 this isn't working for this kernel cycle,
push a minimal patch to back it off, even if the bug is in swiotlb, we
don't just add stuff broken like this, even if it's not
your bug we should have backed off for a kernel or two until we had
the underlying infrastructure fixed. Otherwise we
get what we have now, which is bit of a crappile, because now I've no
idea if the swiotlb things people report are
the false positive, or some new thing.

Dave.
Michel Dänzer May 1, 2018, 1:59 p.m. UTC | #8
On 2018-05-01 01:15 AM, Dave Airlie wrote:
>>
>>
>> Yes, I fixed the original false positive messages myself with the swiotlb
>> maintainer and I was CCed in fixing the recent fallout from Chris changes as
>> well.
> 
> So do we have a good summary of where this at now?
> 
> I'm getting reports on 4.16.4 still displaying these, what hammer do I
> need to hit things with to get 4.16.x+1 to not do this?
> 
> Is there still outstanding issues upstream.

There are, https://patchwork.freedesktop.org/patch/219765/ should
hopefully fix the last of it.


> [...] I've no idea if the swiotlb things people report are the false
> positive, or some new thing.

The issues I've seen reported with 4.16 are false positives from TTM's
perspective, which uses DMA_ATTR_NO_WARN to suppress these warnings, due
to multiple regressions introduced by commit
0176adb004065d6815a8e67946752df4cd947c5b "swiotlb: refactor
 coherent buffer allocation" in 4.16-rc1.
Michel Dänzer May 2, 2018, 8:08 a.m. UTC | #9
On 2018-04-29 01:56 AM, Ilia Mirkin wrote:
> On Sat, Apr 28, 2018 at 7:02 PM, Michel Dänzer <michel@daenzer.net> wrote:
>>
>> Unfortunately, there was an swiotlb regression (not directly related to
>> Christian's work) shortly after this fix, also in 4.16-rc1, which is now
>> fixed in 4.17-rc1 and will be backported to 4.16.y.
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/commit/?h=v4.16.5&id=2c9dacf5bfe1e45d96dfe97cb71d2b717786a7b9
> 
> This guy? Didn't help. I'm running 4.16.4 right now.

Try https://patchwork.freedesktop.org/patch/219765/ .


>>> We now have *two* broken releases, v4.15 and v4.16 (anything that
>>> spews error messages and stack traces ad-infinitum in dmesg is, by
>>> definition, broken).
>>
>> I haven't seen any evidence that there's still an issue in 4.15, is
>> there any?
> 
> Well, I did have a late 4.15 rc kernel in addition to the 'suppress
> warning' patch. Now I'm questioning my memory of whether the issue was
> resolved there or not. I'm pretty sure that 'not', but no longer 100%.

It seems pretty clear it is in fact resolved in 4.15. Even if it indeed
wasn't for you, did you expect us to find out by monitoring you on IRC 24/7?


> As a user who is not in a position to debug this directly due to lack
> of time and knowledge, [...]

I have plenty of other things to do other than looking into this and
coming up with the fix above as well, and I'm no more knowledgeable
about the SWIOTLB code than you.

Anyway, nobody can track down every problem they run into. But let me
kindly ask you to more carefully look at the information available
before deciding which tree to bark up in the future.

Patch
diff mbox

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
index dfd22db13fb1..e03e9e361e2a 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
@@ -988,7 +988,7 @@  static struct ttm_tt *amdgpu_ttm_tt_create(struct ttm_buffer_object *bo,
 		return NULL;
 	}
 	gtt->ttm.ttm.func = &amdgpu_backend_func;
-	if (ttm_sg_tt_init(&gtt->ttm, bo, page_flags)) {
+	if (ttm_sg_tt_init(&gtt->ttm, bo, page_flags | TTM_PAGE_FLAG_TRANSHUGE)) {
 		kfree(gtt);
 		return NULL;
 	}
diff --git a/drivers/gpu/drm/ttm/ttm_page_alloc.c b/drivers/gpu/drm/ttm/ttm_page_alloc.c
index f0481b7b60c5..476d668e1cbd 100644
--- a/drivers/gpu/drm/ttm/ttm_page_alloc.c
+++ b/drivers/gpu/drm/ttm/ttm_page_alloc.c
@@ -760,7 +760,7 @@  static void ttm_put_pages(struct page **pages, unsigned npages, int flags,
 {
 	struct ttm_page_pool *pool = ttm_get_pool(flags, false, cstate);
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
-	struct ttm_page_pool *huge = ttm_get_pool(flags, true, cstate);
+	struct ttm_page_pool *huge = NULL;
 #endif
 	unsigned long irq_flags;
 	unsigned i;
@@ -780,7 +780,8 @@  static void ttm_put_pages(struct page **pages, unsigned npages, int flags,
 			}
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
-			if (!(flags & TTM_PAGE_FLAG_DMA32)) {
+			if ((flags & (TTM_PAGE_FLAG_DMA32 | TTM_PAGE_FLAG_TRANSHUGE)) ==
+			    TTM_PAGE_FLAG_TRANSHUGE) {
 				for (j = 0; j < HPAGE_PMD_NR; ++j)
 					if (p++ != pages[i + j])
 					    break;
@@ -805,6 +806,8 @@  static void ttm_put_pages(struct page **pages, unsigned npages, int flags,
 
 	i = 0;
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
+	if (flags & TTM_PAGE_FLAG_TRANSHUGE)
+		huge = ttm_get_pool(flags, true, cstate);
 	if (huge) {
 		unsigned max_size, n2free;
 
@@ -877,7 +880,7 @@  static int ttm_get_pages(struct page **pages, unsigned npages, int flags,
 {
 	struct ttm_page_pool *pool = ttm_get_pool(flags, false, cstate);
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
-	struct ttm_page_pool *huge = ttm_get_pool(flags, true, cstate);
+	struct ttm_page_pool *huge = NULL;
 #endif
 	struct list_head plist;
 	struct page *p = NULL;
@@ -906,7 +909,8 @@  static int ttm_get_pages(struct page **pages, unsigned npages, int flags,
 
 		i = 0;
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
-		if (!(gfp_flags & GFP_DMA32)) {
+		if ((flags & (TTM_PAGE_FLAG_DMA32 | TTM_PAGE_FLAG_TRANSHUGE)) ==
+		    TTM_PAGE_FLAG_TRANSHUGE) {
 			while (npages >= HPAGE_PMD_NR) {
 				gfp_t huge_flags = gfp_flags;
 
@@ -933,9 +937,13 @@  static int ttm_get_pages(struct page **pages, unsigned npages, int flags,
 				return -ENOMEM;
 			}
 
-			/* Swap the pages if we detect consecutive order */
-			if (i > first && pages[i - 1] == p - 1)
-				swap(p, pages[i - 1]);
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+			if (flags & TTM_PAGE_FLAG_TRANSHUGE) {
+				/* Swap the pages if we detect consecutive order */
+				if (i > first && pages[i - 1] == p - 1)
+					swap(p, pages[i - 1]);
+			}
+#endif
 
 			pages[i++] = p;
 			--npages;
@@ -946,6 +954,8 @@  static int ttm_get_pages(struct page **pages, unsigned npages, int flags,
 	count = 0;
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
+	if (flags & TTM_PAGE_FLAG_TRANSHUGE)
+		huge = ttm_get_pool(flags, true, cstate);
 	if (huge && npages >= HPAGE_PMD_NR) {
 		INIT_LIST_HEAD(&plist);
 		ttm_page_pool_get_pages(huge, &plist, flags, cstate,
@@ -969,9 +979,14 @@  static int ttm_get_pages(struct page **pages, unsigned npages, int flags,
 	list_for_each_entry(p, &plist, lru) {
 		struct page *tmp = p;
 
-		/* Swap the pages if we detect consecutive order */
-		if (count > first && pages[count - 1] == tmp - 1)
-			swap(tmp, pages[count - 1]);
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+		if (flags & TTM_PAGE_FLAG_TRANSHUGE) {
+			/* Swap the pages if we detect consecutive order */
+			if (count > first && pages[count - 1] == tmp - 1)
+				swap(tmp, pages[count - 1]);
+		}
+#endif
+
 		pages[count++] = tmp;
 	}
 
diff --git a/drivers/gpu/drm/ttm/ttm_page_alloc_dma.c b/drivers/gpu/drm/ttm/ttm_page_alloc_dma.c
index 8a25d1974385..291b04213ec5 100644
--- a/drivers/gpu/drm/ttm/ttm_page_alloc_dma.c
+++ b/drivers/gpu/drm/ttm/ttm_page_alloc_dma.c
@@ -949,7 +949,8 @@  int ttm_dma_populate(struct ttm_dma_tt *ttm_dma, struct device *dev,
 	type = ttm_to_type(ttm->page_flags, ttm->caching_state);
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
-	if (ttm->page_flags & TTM_PAGE_FLAG_DMA32)
+	if ((ttm->page_flags & (TTM_PAGE_FLAG_DMA32 | TTM_PAGE_FLAG_TRANSHUGE))
+	    != TTM_PAGE_FLAG_TRANSHUGE)
 		goto skip_huge;
 
 	pool = ttm_dma_find_pool(dev, type | IS_HUGE);
@@ -1035,7 +1036,7 @@  void ttm_dma_unpopulate(struct ttm_dma_tt *ttm_dma, struct device *dev)
 {
 	struct ttm_tt *ttm = &ttm_dma->ttm;
 	struct ttm_mem_global *mem_glob = ttm->bdev->glob->mem_glob;
-	struct dma_pool *pool;
+	struct dma_pool *pool = NULL;
 	struct dma_page *d_page, *next;
 	enum pool_type type;
 	bool is_cached = false;
@@ -1045,7 +1046,8 @@  void ttm_dma_unpopulate(struct ttm_dma_tt *ttm_dma, struct device *dev)
 	type = ttm_to_type(ttm->page_flags, ttm->caching_state);
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
-	pool = ttm_dma_find_pool(dev, type | IS_HUGE);
+	if (ttm->page_flags & TTM_PAGE_FLAG_TRANSHUGE)
+		pool = ttm_dma_find_pool(dev, type | IS_HUGE);
 	if (pool) {
 		count = 0;
 		list_for_each_entry_safe(d_page, next, &ttm_dma->pages_list,
diff --git a/include/drm/ttm/ttm_tt.h b/include/drm/ttm/ttm_tt.h
index c0e928abf592..c7d2120f0362 100644
--- a/include/drm/ttm/ttm_tt.h
+++ b/include/drm/ttm/ttm_tt.h
@@ -41,6 +41,7 @@  struct ttm_operation_ctx;
 #define TTM_PAGE_FLAG_DMA32           (1 << 7)
 #define TTM_PAGE_FLAG_SG              (1 << 8)
 #define TTM_PAGE_FLAG_NO_RETRY	      (1 << 9)
+#define TTM_PAGE_FLAG_TRANSHUGE       (1 << 10)
 
 enum ttm_caching_state {
 	tt_uncached,