From: Joonas Lahtinen Date: Wed, 10 May 2017 11:00:40 +0000 (+0300) Subject: drm/i915: Do not sync RCU during shrinking X-Git-Tag: v4.13-rc1~73^2~28^2~72 X-Git-Url: https://asedeno.scripts.mit.edu/gitweb/?a=commitdiff_plain;h=73cc0b9aa9afa5ba65d92e46ded61d29430d72a4;p=linux.git drm/i915: Do not sync RCU during shrinking 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 (0eafec6d3244) v2: More information to commit message. v3: Remove "grep _rcu_" escapee from i915_gem_shrink_all (Andrea) Fixes: c053b5a506d3 ("drm/i915: Don't call synchronize_rcu_expedited under struct_mutex") Suggested-by: Chris Wilson Reported-by: J. R. Okajima Signed-off-by: Joonas Lahtinen Reviewed-by: Chris Wilson Tested-by: Hugh Dickins Tested-by: Andrea Arcangeli Cc: Chris Wilson Cc: Tvrtko Ursulin Cc: J. R. Okajima Cc: Andrea Arcangeli Cc: Hugh Dickins Cc: Jani Nikula Cc: # v4.11+ Link: http://patchwork.freedesktop.org/patch/msgid/1494414040-11160-1-git-send-email-joonas.lahtinen@linux.intel.com --- diff --git a/drivers/gpu/drm/i915/i915_gem_shrinker.c b/drivers/gpu/drm/i915/i915_gem_shrinker.c index 0e7352d82ca4..b409e67c5c72 100644 --- a/drivers/gpu/drm/i915/i915_gem_shrinker.c +++ b/drivers/gpu/drm/i915/i915_gem_shrinker.c @@ -59,9 +59,6 @@ static void shrinker_unlock(struct drm_i915_private *dev_priv, bool unlock) return; mutex_unlock(&dev_priv->drm.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; }