[Intel-gfx] [PATCH 07/38] drm/i915: Stop tracking MRU activity on VMA

[Chris Wilson]

Quoting Tvrtko Ursulin (2019-01-18 16:03:27)
> 
> On 18/01/2019 14:00, Chris Wilson wrote:
> > Our goal is to remove struct_mutex and replace it with fine grained
> > locking. One of the thorny issues is our eviction logic for reclaiming
> > space for an execbuffer (or GTT mmaping, among a few other examples).
> > While eviction itself is easy to move under a per-VM mutex, performing
> > the activity tracking is less agreeable. One solution is not to do any
> > MRU tracking and do a simple coarse evaluation during eviction of
> > active/inactive, with a loose temporal ordering of last
> > insertion/evaluation. That keeps all the locking constrained to when we
> > are manipulating the VM itself, neatly avoiding the tricky handling of
> > possible recursive locking during execbuf and elsewhere.
> > 
> > Note that discarding the MRU is unlikely to impact upon our efficiency
> > to reclaim VM space (where we think a LRU model is best) as our
> > current strategy is to use random idle replacement first before doing
> > a search, and over time the use of softpinned 48b per-ppGTT is growing
> > (thereby eliminating any need to perform any eviction searches, in
> > theory at least).
> 
> There is still no mention of list consolidation.

"Note that discarding the MRU (currently implemented as a pair of lists,
to avoid scanning the active list for a NONBLOCKING search)"

Is that enough to make it clear?
-Chris