Skip to content
  • Tejun Heo's avatar
    blkcg: unify blkg's for blkcg policies · e8989fae
    Tejun Heo authored
    Currently, blkg is per cgroup-queue-policy combination.  This is
    unnatural and leads to various convolutions in partially used
    duplicate fields in blkg, config / stat access, and general management
    of blkgs.
    This patch make blkg's per cgroup-queue and let them serve all
    policies.  blkgs are now created and destroyed by blkcg core proper.
    This will allow further consolidation of common management logic into
    blkcg core and API with better defined semantics and layering.
    As a transitional step to untangle blkg management, elvswitch and
    policy [de]registration, all blkgs except the root blkg are being shot
    down during elvswitch and bypass.  This patch adds blkg_root_update()
    to update root blkg in place on policy change.  This is hacky and racy
    but should be good enough as interim step until we get locking
    simplified and switch over to proper in-place update for all blkgs.
    -v2: Root blkgs need to be updated on elvswitch too and blkg_alloc()
         comment wasn't updated according to the function change.  Fixed.
         Both pointed out by Vivek.
    -v3: v2 updated blkg_destroy_all() to invoke update_root_blkg_pd() for
         all policies.  This freed root pd during elvswitch before the
         last queue finished exiting and led to oops.  Directly invoke
         update_root_blkg_pd() only on BLKIO_POLICY_PROP from
         cfq_exit_queue().  This also is closer to what will be done with
         proper in-place blkg update.  Reported by Vivek.
    Signed-off-by: default avatarTejun Heo <>
    Cc: Vivek Goyal <>
    Signed-off-by: default avatarJens Axboe <>