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drm/i915: Do not sync RCU during shrinking

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Due to the complex dependencies between workqueues and RCU, which
are not easily detected by lockdep, do not synchronize RCU during
shrinking.

On low-on-memory systems (mem=1G for example), the RCU sync leads
to all system workqueus freezing and unrelated lockdep splats are
displayed according to reports. GIT bisecting done by J. R.
Okajima points to the commit where RCU syncing was extended.

RCU sync gains us very little benefit in real life scenarios
where the amount of memory used by object backing storage is
dominant over the metadata under RCU, so drop it altogether.

 " Yeeeaah, if core could just, go ahead and reclaim RCU
   queues, that'd be great. "

  - Chris Wilson, 2016 (0eafec6d32)

v2: More information to commit message.
v3: Remove "grep _rcu_" escapee from i915_gem_shrink_all (Andrea)

Fixes: c053b5a506 ("drm/i915: Don't call synchronize_rcu_expedited under struct_mutex")
Suggested-by: Chris Wilson <chris@chris-wilson.co.uk>
Reported-by: J. R. Okajima <hooanon05g@gmail.com>
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Tested-by: Hugh Dickins <hughd@google.com>
Tested-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: J. R. Okajima <hooanon05g@gmail.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: <stable@vger.kernel.org> # v4.11+
(cherry picked from commit 73cc0b9aa9)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1495097379-573-1-git-send-email-joonas.lahtinen@linux.intel.com
This commit is contained in:
Joonas Lahtinen
2017-05-18 11:49:39 +03:00
committed by Jani Nikula
parent 2f720aac93
commit 4681ee21d6
1 changed files with 0 additions and 5 deletions
Download Patch File Download Diff File Expand all files Collapse all files

5
drivers/gpu/drm/i915/i915_gem_shrinker.c
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@ -59,9 +59,6 @@ static void i915_gem_shrinker_unlock(struct drm_device *dev, bool unlock)
return;
mutex_unlock(&dev->struct_mutex);
/* expedite the RCU grace period to free some request slabs */
synchronize_rcu_expedited();
}
static bool any_vma_pinned(struct drm_i915_gem_object *obj)
@ -274,8 +271,6 @@ unsigned long i915_gem_shrink_all(struct drm_i915_private *dev_priv)
I915_SHRINK_ACTIVE);
intel_runtime_pm_put(dev_priv);
synchronize_rcu(); /* wait for our earlier RCU delayed slab frees */
return freed;
}