Re: [PATCH] drm/i915: Reduce memory pressure during shrinker by preallocating swizzle pages

[Chris Wilson <chris@chris-wilson.co.uk>]

On Mon, 3 Dec 2012 18:29:30 +0100, Daniel Vetter <daniel@ffwll.ch> wrote:
> On Mon, Dec 03, 2012 at 04:30:59PM +0000, Chris Wilson wrote:
> > On a machine with bit17 swizzling, we need to store the bit17 of the
> > physical page address in put-pages. This requires a memory allocation,
> > on average less than a page, which may be difficult to satisfy is the
> > request to put-pages is on behalf of the shrinker. We could allow that
> > allocation to pull from the reserved memory pools, but it seems much
> > safer to preallocate the array for tiled objects on affected machines.
> > 
> > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> > ---
> >  drivers/gpu/drm/i915/i915_gem_tiling.c |   14 ++++++++++++++
> >  1 file changed, 14 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/i915/i915_gem_tiling.c b/drivers/gpu/drm/i915/i915_gem_tiling.c
> > index 8e59bb5..140ef6b 100644
> > --- a/drivers/gpu/drm/i915/i915_gem_tiling.c
> > +++ b/drivers/gpu/drm/i915/i915_gem_tiling.c
> > @@ -351,6 +351,20 @@ i915_gem_set_tiling(struct drm_device *dev, void *data,
> >  	/* we have to maintain this existing ABI... */
> >  	args->stride = obj->stride;
> >  	args->tiling_mode = obj->tiling_mode;
> > +
> > +	/* Try to preallocate memory required to save swizzling on put-pages */
> > +	if (dev_priv->mm.bit_6_swizzle_x == I915_BIT_6_SWIZZLE_9_10_17) {
> > +		if (obj->tiling_mode) {
> 
> i915_gem_object_needs_bit17_swizzle not suitable?

No, it takes the current obj->tiling_mode. Well, originally this was
using args->tiling_mode, but that fell by the wayside. Still I thought
it would be useful to be able to discard the memory allocated when we
release the tiling.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre