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commit4681ee21d6upstream. 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> (cherry picked from commit73cc0b9aa9) 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 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.