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    drm/i915: Revert shrinker changes from "Track unbound pages" · 93927ca5
    Daniel Vetter 提交于
    This partially reverts
    
    commit 6c085a72
    Author: Chris Wilson <chris@chris-wilson.co.uk>
    Date:   Mon Aug 20 11:40:46 2012 +0200
    
        drm/i915: Track unbound pages
    
    Closer inspection of that patch revealed a bunch of unrelated changes
    in the shrinker:
    - The shrinker count is now in pages instead of objects.
    - For counting the shrinkable objects the old code only looked at the
      inactive list, the new code looks at all bounds objects (including
      pinned ones). That is obviously in addition to the new unbound list.
    - The shrinker cound is no longer scaled with
      sysctl_vfs_cache_pressure. Note though that with the default tuning
      value of vfs_cache_pressue = 100 this doesn't affect the shrinker
      behaviour.
    - When actually shrinking objects, the old code first dropped
      purgeable objects, then normal (inactive) objects. Only then did it,
      in a last-ditch effort idle the gpu and evict everything. The new
      code omits the intermediate step of evicting normal inactive
      objects.
    
    Safe for the first change, which seems benign, and the shrinker count
    scaling, which is a bit a different story, the endresult of all these
    changes is that the shrinker is _much_ more likely to fall back to the
    last-ditch resort of idling the gpu and evicting everything.  The old
    code could only do that if something else evicted lots of objects
    meanwhile (since without any other changes the nr_to_scan will be
    smaller than the object count).
    
    Reverting the vfs_cache_pressure behaviour itself is a bit bogus: Only
    dentry/inode object caches should scale their shrinker counts with
    vfs_cache_pressure. Originally I've had that change reverted, too. But
    Chris Wilson insisted that it's too bogus and shouldn't again see the
    light of day.
    
    Hence revert all these other changes and restore the old shrinker
    behaviour, with the minor adjustment that we now first scan the
    unbound list, then the inactive list for each object category
    (purgeable or normal).
    
    A similar patch has been tested by a few people affected by the gen4/5
    hangs which started to appear in 3.7, which some people bisected to
    the "drm/i915: Track unbound pages" commit. But just disabling the
    unbound logic alone didn't change things at all.
    
    Note that this patch doesn't fix the referenced bugs, it only hides
    the underlying bug(s) well enough to restore pre-3.7 behaviour. The
    key to achieve that is to massively reduce the likelyhood of going
    into a full gpu stall and evicting everything.
    
    v2: Reword commit message a bit, taking Chris Wilson's comment into
    account.
    
    v3: On Chris Wilson's insistency, do not reinstate the rather bogus
    vfs_cache_pressure change.
    Tested-by: NGreg KH <gregkh@linuxfoundation.org>
    Tested-by: NDave Kleikamp <dave.kleikamp@oracle.com>
    References: https://bugs.freedesktop.org/show_bug.cgi?id=55984
    References: https://bugs.freedesktop.org/show_bug.cgi?id=57122
    References: https://bugs.freedesktop.org/show_bug.cgi?id=56916
    References: https://bugs.freedesktop.org/show_bug.cgi?id=57136
    Cc: Chris Wilson <chris@chris-wilson.co.uk>
    Cc: stable@vger.kernel.org
    Acked-by: NChris Wilson <chris@chris-wilson.co.uk>
    Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>
    93927ca5
i915_gem.c 109.8 KB