linux-kernel - Re: [PATCH 2/2] drm/i915: Mark pinned shmemfs pages as unevictable

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Date:   Tue, 16 Oct 2018 21:13:50 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Chris Wilson <chris@...is-wilson.co.uk>
Cc:     Kuo-Hsin Yang <vovoy@...omium.org>, linux-kernel@...r.kernel.org,
        intel-gfx@...ts.freedesktop.org, linux-mm@...ck.org,
        akpm@...ux-foundation.org, peterz@...radead.org,
        dave.hansen@...el.com, corbet@....net, hughd@...gle.com,
        joonas.lahtinen@...ux.intel.com, marcheu@...omium.org,
        hoegsberg@...omium.org
Subject: Re: [PATCH 2/2] drm/i915: Mark pinned shmemfs pages as unevictable

On Tue 16-10-18 19:31:06, Chris Wilson wrote:
> Quoting Michal Hocko (2018-10-16 19:21:55)
> > On Wed 17-10-18 01:43:00, Kuo-Hsin Yang wrote:
> > > The i915 driver use shmemfs to allocate backing storage for gem objects.
> > > These shmemfs pages can be pinned (increased ref count) by
> > > shmem_read_mapping_page_gfp(). When a lot of pages are pinned, vmscan
> > > wastes a lot of time scanning these pinned pages. Mark these pinned
> > > pages as unevictable to speed up vmscan.
> > 
> > I would squash the two patches into the single one. One more thing
> > though. One more thing to be careful about here. Unless I miss something
> > such a page is not migrateable so it shouldn't be allocated from a
> > movable zone. Does mapping_gfp_constraint contains __GFP_MOVABLE? If
> > yes, we want to drop it as well. Other than that the patch makes sense
> > with my very limited knowlege of the i915 code of course.
> 
> They are not migrateable today. But we have proposed hooking up
> .migratepage and setting __GFP_MOVABLE which would then include unlocking
> the mapping at migrate time.

if the mapping_gfp doesn't include __GFP_MOVABLE today then there is no
issue I've had in mind.
-- 
Michal Hocko
SUSE Labs