[Intel-gfx] [PATCH 04/11] drm/i915: Make request allocation caches global

[Chris Wilson]

Quoting Tvrtko Ursulin (2019-02-27 10:29:43)
> 
> On 26/02/2019 10:23, Chris Wilson wrote:
> > As kmem_caches share the same properties (size, allocation/free behaviour)
> > for all potential devices, we can use global caches. While this
> > potential has worse fragmentation behaviour (one can argue that
> > different devices would have different activity lifetimes, but you can
> > also argue that activity is temporal across the system) it is the
> > default behaviour of the system at large to amalgamate matching caches.
> > 
> > The benefit for us is much reduced pointer dancing along the frequent
> > allocation paths.
> > 
> > v2: Defer shrinking until after a global grace period for futureproofing
> > multiple consumers of the slab caches, similar to the current strategy
> > for avoiding shrinking too early.
> 
> I suggested to call i915_globals_park directly from __i915_gem_park for 
> symmetry with how i915_gem_unpark calls i915_globals_unpark. 
> i915_globals has it's own delayed setup so I don't think it benefits 
> from the double indirection courtesy of being called from shrink_caches.

I replied I left that change until a later patch after the final
conversions. Mostly so that we had a standalone patch to revert if the
rcu_work turns out badly. In this patch, it was to be the simple
translation over to global_shrink, except you asked for it to be truly
global and so we needed another layer of counters.
-Chris