Re: [RFC] mm,drm/i915: Mark pinned shmemfs pages as unevictable

From: Chris Wilson <chris@chris-wilson.co.uk>
To: Michal Hocko <mhocko@suse.com>
Cc: intel-gfx@lists.freedesktop.org, linux-mm@kvack.org,
	Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
	Matthew Auld <matthew.auld@intel.com>,
	Dave Hansen <dave.hansen@intel.com>,
	"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Peter Zijlstra <peterz@infradead.org>
Subject: Re: [RFC] mm,drm/i915: Mark pinned shmemfs pages as unevictable
Date: Mon, 21 Aug 2017 16:03:31 +0100	[thread overview]
Message-ID: <150332781184.13047.15448500819676507290@mail.alporthouse.com> (raw)
In-Reply-To: <20170821140641.GN25956@dhcp22.suse.cz>

Quoting Michal Hocko (2017-08-21 15:06:42)
> 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.

My googlefu says "[RFC][PATCH 1/5] mm: Introduce VM_PINNED and
interfaces" is the series, and it certainly targets the very same
problem.

Peter, is that the latest version?
-Chris

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