Re: [PATCH v2] drm/i915: Disable shrinker for non-swapped backed objects

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

On Wed, Nov 25, 2015 at 02:06:10PM -0500, Johannes Weiner wrote:
> On Wed, Nov 25, 2015 at 06:36:56PM +0000, Chris Wilson wrote:
> > If the system has no available swap pages, we cannot make forward
> > progress in the shrinker by releasing active pages, only by releasing
> > purgeable pages which are immediately reaped. Take total_swap_pages into
> > account when counting up available objects to be shrunk and subsequently
> > shrinking them. By doing so, we avoid unbinding objects that cannot be
> > shrunk and so wasting CPU cycles flushing those objects from the GPU to
> > the system and then immediately back again (as they will more than
> > likely be reused shortly after).
> > 
> > Based on a patch by Akash Goel.
> > 
> > v2: Check for frontswap without physical swap (or dedicated swap space).
> > If frontswap is available, we may be able to compress the GPU pages
> > instead of swapping out to disk. In this case, we do want to shrink GPU
> > objects and so make them available for compressing.
> 
> Frontswap always sits on top of an active swap device. It's enough to
> check for available swap space.
> 
> > +static bool swap_available(void)
> > +{
> > +	return total_swap_pages || frontswap_enabled;
> > +}
> 
> If you use get_nr_swap_pages() instead of total_swap_pages, this will
> also stop scanning objects once the swap space is full. We do that in
> the VM to stop scanning anonymous pages.

Thanks. Would EXPORT_SYMBOL_GPL(nr_swap_pages) (or equivalent) be
acceptable?
-Chris
 
-- 
Chris Wilson, Intel Open Source Technology Centre

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