• Tejun Heo's avatar
    blkcg: implement per-queue policy activation · a2b1693b
    Tejun Heo authored
    
    
    All blkcg policies were assumed to be enabled on all request_queues.
    Due to various implementation obstacles, during the recent blkcg core
    updates, this was temporarily implemented as shooting down all !root
    blkgs on elevator switch and policy [de]registration combined with
    half-broken in-place root blkg updates.  In addition to being buggy
    and racy, this meant losing all blkcg configurations across those
    events.
    
    Now that blkcg is cleaned up enough, this patch replaces the temporary
    implementation with proper per-queue policy activation.  Each blkcg
    policy should call the new blkcg_[de]activate_policy() to enable and
    disable the policy on a specific queue.  blkcg_activate_policy()
    allocates and installs policy data for the policy for all existing
    blkgs.  blkcg_deactivate_policy() does the reverse.  If a policy is
    not enabled for a given queue, blkg printing / config functions skip
    the respective blkg for the queue.
    
    blkcg_activate_policy() also takes care of root blkg creation, and
    cfq_init_queue() and blk_throtl_init() are updated accordingly.
    
    This replaces blkcg_bypass_{start|end}() and update_root_blkg_pd()
    unnecessary.  Dropped.
    
    v2: cfq_init_queue() was returning uninitialized @ret on root_group
        alloc failure if !CONFIG_CFQ_GROUP_IOSCHED.  Fixed.
    Signed-off-by: default avatarTejun Heo <tj@kernel.org>
    Cc: Vivek Goyal <vgoyal@redhat.com>
    Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
    a2b1693b