linux-kernel - Re: [PATCH v3] mm, drm/i915: mark pinned shmemfs pages as unevictable

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Date:   Fri, 2 Nov 2018 21:22:46 +0800
From:   Vovo Yang <vovoy@...omium.org>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     linux-kernel@...r.kernel.org, intel-gfx@...ts.freedesktop.org,
        linux-mm@...ck.org, Chris Wilson <chris@...is-wilson.co.uk>,
        Michal Hocko <mhocko@...e.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v3] mm, drm/i915: mark pinned shmemfs pages as unevictable

On Thu, Nov 1, 2018 at 10:30 PM Dave Hansen <dave.hansen@...el.com> wrote:
> On 11/1/18 5:06 AM, Vovo Yang wrote:
> >> mlock() and ramfs usage are pretty easy to track down.  /proc/$pid/smaps
> >> or /proc/meminfo can show us mlock() and good ol' 'df' and friends can
> >> show us ramfs the extent of pinned memory.
> >>
> >> With these, if we see "Unevictable" in meminfo bump up, we at least have
> >> a starting point to find the cause.
> >>
> >> Do we have an equivalent for i915?

Chris helped to answer this question:
Though it includes a few non-shmemfs objects, see
debugfs/dri/0/i915_gem_objects and the "bound objects".

Example i915_gem_object output:
  591 objects, 95449088 bytes
  55 unbound objects, 1880064 bytes
  533 bound objects, 93040640 bytes
  ...

> > AFAIK, there is no way to get i915 unevictable page count, some
> > modification to i915 debugfs is required.
>
> Is something like this feasible to add to this patch set before it gets
> merged?  For now, it's probably easy to tell if i915 is at fault because
> if the unevictable memory isn't from mlock or ramfs, it must be i915.
>
> But, if we leave it as-is, it'll just defer the issue to the fourth user
> of the unevictable list, who will have to come back and add some
> debugging for this.
>
> Seems prudent to just do it now.