[Intel-gfx] [RFC] mm, drm/i915: Mark pinned shmemfs pages as unevictable

[Michal Hocko]

On Sat 19-08-17 14:15:35, Chris Wilson wrote:
> Quoting Michal Hocko (2017-06-06 13:14:18)
> > On Tue 06-06-17 13:04:36, Chris Wilson wrote:
> > > Similar in principle to the treatment of get_user_pages, pages that
> > > i915.ko acquires from shmemfs are not immediately reclaimable and so
> > > should be excluded from the mm accounting and vmscan until they have
> > > been returned to the system via shrink_slab/i915_gem_shrink. By moving
> > > the unreclaimable pages off the inactive anon lru, not only should
> > > vmscan be improved by avoiding walking unreclaimable pages, but the
> > > system should also have a better idea of how much memory it can reclaim
> > > at that moment in time.
> > 
> > That is certainly desirable. Peter has proposed a generic pin_page (or
> > similar) API. What happened with it? I think it would be a better
> > approach than (ab)using mlock API. I am also not familiar with the i915
> > code to be sure that using lock_page is really safe here. I think that
> > all we need is to simply move those pages in/out to/from unevictable LRU
> > list on pin/unpining.
> 
> I just had the opportunity to try this mlock_vma_page() hack on a
> borderline swapping system (i.e. lots of vmpressure between i915 buffers
> and the buffercache), and marking the i915 pages as unevictable makes a
> huge difference in avoiding stalls in direct reclaim across the system.
> 
> Reading back over the thread, it seems that the simplest approach going
> forward is a small api for managing the pages on the unevictable LRU?

Yes and I thought that pin_page API would do exactly that.
-- 
Michal Hocko
SUSE Labs