[PATCH 8/9] drm/ttm: Don't count pages in SG BOs against pages_limit
Daniel Vetter
daniel at ffwll.ch
Wed Apr 14 12:47:19 UTC 2021
On Wed, Apr 14, 2021 at 2:43 PM Christian König
<christian.koenig at amd.com> wrote:
>
> Am 14.04.21 um 14:25 schrieb Daniel Vetter:
> > On Wed, Apr 14, 2021 at 12:49 PM Christian König
> > <ckoenig.leichtzumerken at gmail.com> wrote:
> >> Am 14.04.21 um 12:26 schrieb Daniel Vetter:
> >>> On Wed, Apr 14, 2021 at 11:19:41AM +0200, Christian König wrote:
> >>>> Am 14.04.21 um 11:15 schrieb Daniel Vetter:
> >>>>> On Wed, Apr 14, 2021 at 08:51:51AM +0200, Christian König wrote:
> >>>>>> Am 14.04.21 um 08:48 schrieb Felix Kuehling:
> >>>>>>> Pages in SG BOs were not allocated by TTM. So don't count them against
> >>>>>>> TTM's pages limit.
> >>>>>>>
> >>>>>>> Signed-off-by: Felix Kuehling <Felix.Kuehling at amd.com>
> >>>>>> Reviewed-by: Christian König <christian.koenig at amd.com>
> >>>>>>
> >>>>>> Going to pick that one up for inclusion in drm-misc-next.
> >>>>> See my other email, but why do we need this? A bit more explanation is imo
> >>>>> needed here at least, since we still need to guarantee that allocations
> >>>>> don't over the limit in total for all gpu buffers together. At least until
> >>>>> the shrinker has landed.
> >>>>>
> >>>>> And this here just opens up the barn door without any explanation why it's
> >>>>> ok.
> >>>> The SG based BOs might not even be backed by pages. E.g. exported VRAM.
> >>>>
> >>>> So either they are exported by a driver which should have accounted for the
> >>>> allocation, exported by TTM which already did the accounting or doesn't even
> >>>> point to pages at all.
> >>>>
> >>>> This is really a bug fix to recreate the behavior we had before moving the
> >>>> accounting to this place.
> >>> Throw that into the commit message and a-b: me. Ideally with a Fixes: line
> >>> or so pointing at the offending commit that broke stuff. Commit messages
> >>> should really go into more detail when there's an entire story behind a
> >>> small change like this one.
> >> Sorry I though that this would be obvious :)
> >>
> >> I've already pushed the patch in the morning, but going to keep that in
> >> mind for the next time.
> > I'll keep reminding you to pls elaborate more in commit messages, it's
> > coming up every once in a while :-)
>
> Well, describing stuff in a commit message which is obvious is just
> redundant.
>
> I can of course explain the whole background of the code in question in
> the commit message, but for obvious bug fixes like this it is just overkill.
>
> > Also in general I think a few days of letting patches soak out there,
> > especially shared code, is good curtesy. Some folks demand 2 weeks,
> > which I think is too much, but less than 24h just means you're
> > guaranteed to leave out half the globe with their feedback. Which
> > isn't great.
>
> Well for structural changes I certainly agree, but not for a bug fix
> which adds a missing check for a special case.
Well if it's a bugfix should at least indicate that, and regression
fixes should come with Fixes: tags. Obvious for you who screamed at
the code is generally not implying it's obvious for anyone else. So
yeah I think in general more explanations would be good.
-Daniel
>
> Christian.
>
> >
> > Driver code I don't care since there you know all the stakeholders ofc.
> > -Daniel
> >
> >> Christian.
> >>
> >>> -Daniel
> >>>
> >>>> Christian.
> >>>>
> >>>>> -Daniel
> >>>>>
> >>>>>> Regards,
> >>>>>> Christian.
> >>>>>>
> >>>>>>> ---
> >>>>>>> drivers/gpu/drm/ttm/ttm_tt.c | 27 ++++++++++++++++++---------
> >>>>>>> 1 file changed, 18 insertions(+), 9 deletions(-)
> >>>>>>>
> >>>>>>> diff --git a/drivers/gpu/drm/ttm/ttm_tt.c b/drivers/gpu/drm/ttm/ttm_tt.c
> >>>>>>> index 5d8820725b75..e8b8c3257392 100644
> >>>>>>> --- a/drivers/gpu/drm/ttm/ttm_tt.c
> >>>>>>> +++ b/drivers/gpu/drm/ttm/ttm_tt.c
> >>>>>>> @@ -317,9 +317,12 @@ int ttm_tt_populate(struct ttm_device *bdev,
> >>>>>>> if (ttm_tt_is_populated(ttm))
> >>>>>>> return 0;
> >>>>>>> - atomic_long_add(ttm->num_pages, &ttm_pages_allocated);
> >>>>>>> - if (bdev->pool.use_dma32)
> >>>>>>> - atomic_long_add(ttm->num_pages, &ttm_dma32_pages_allocated);
> >>>>>>> + if (!(ttm->page_flags & TTM_PAGE_FLAG_SG)) {
> >>>>>>> + atomic_long_add(ttm->num_pages, &ttm_pages_allocated);
> >>>>>>> + if (bdev->pool.use_dma32)
> >>>>>>> + atomic_long_add(ttm->num_pages,
> >>>>>>> + &ttm_dma32_pages_allocated);
> >>>>>>> + }
> >>>>>>> while (atomic_long_read(&ttm_pages_allocated) > ttm_pages_limit ||
> >>>>>>> atomic_long_read(&ttm_dma32_pages_allocated) >
> >>>>>>> @@ -350,9 +353,12 @@ int ttm_tt_populate(struct ttm_device *bdev,
> >>>>>>> return 0;
> >>>>>>> error:
> >>>>>>> - atomic_long_sub(ttm->num_pages, &ttm_pages_allocated);
> >>>>>>> - if (bdev->pool.use_dma32)
> >>>>>>> - atomic_long_sub(ttm->num_pages, &ttm_dma32_pages_allocated);
> >>>>>>> + if (!(ttm->page_flags & TTM_PAGE_FLAG_SG)) {
> >>>>>>> + atomic_long_sub(ttm->num_pages, &ttm_pages_allocated);
> >>>>>>> + if (bdev->pool.use_dma32)
> >>>>>>> + atomic_long_sub(ttm->num_pages,
> >>>>>>> + &ttm_dma32_pages_allocated);
> >>>>>>> + }
> >>>>>>> return ret;
> >>>>>>> }
> >>>>>>> EXPORT_SYMBOL(ttm_tt_populate);
> >>>>>>> @@ -382,9 +388,12 @@ void ttm_tt_unpopulate(struct ttm_device *bdev, struct ttm_tt *ttm)
> >>>>>>> else
> >>>>>>> ttm_pool_free(&bdev->pool, ttm);
> >>>>>>> - atomic_long_sub(ttm->num_pages, &ttm_pages_allocated);
> >>>>>>> - if (bdev->pool.use_dma32)
> >>>>>>> - atomic_long_sub(ttm->num_pages, &ttm_dma32_pages_allocated);
> >>>>>>> + if (!(ttm->page_flags & TTM_PAGE_FLAG_SG)) {
> >>>>>>> + atomic_long_sub(ttm->num_pages, &ttm_pages_allocated);
> >>>>>>> + if (bdev->pool.use_dma32)
> >>>>>>> + atomic_long_sub(ttm->num_pages,
> >>>>>>> + &ttm_dma32_pages_allocated);
> >>>>>>> + }
> >>>>>>> ttm->page_flags &= ~TTM_PAGE_FLAG_PRIV_POPULATED;
> >>>>>>> }
> >>>>>> _______________________________________________
> >>>>>> dri-devel mailing list
> >>>>>> dri-devel at lists.freedesktop.org
> >>>>>> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flists.freedesktop.org%2Fmailman%2Flistinfo%2Fdri-devel&data=04%7C01%7Cchristian.koenig%40amd.com%7C503f240d409740c1333508d8ff406545%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637539999355330481%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=6sW53%2FGpxk4rZKM7mpHDfgBhreCXY4McypKGqTH13b8%3D&reserved=0
> >
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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