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

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