[PATCH 8/9] drm/ttm: Don't count pages in SG BOs against pages_limit

[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 :-)

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.

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%7C3075d7fd16644322a13608d8ff25d59b%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637539885255795187%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=KOnHA1CbNFjjMZR2rgHmGkH%2B7C84YCtA6u9V1wBAay4%3D&reserved=0
>


-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch