• Tejun Heo's avatar
    blkcg: add blkg_[rw]stat->aux_cnt and replace cfq_group->dead_stats with it · e6269c44
    Tejun Heo authored
    
    
    cgroup stats are local to each cgroup and doesn't propagate to
    ancestors by default.  When recursive stats are necessary, the sum is
    calculated over all the descendants.  This initially was for backward
    compatibility to support both group-local and recursive stats but this
    mode of operation makes general sense as stat update is much hotter
    thafn reporting those stats.
    
    This however ends up losing recursive stats when a child is removed.
    To work around this, cfq-iosched adds its stats to its parent
    cfq_group->dead_stats which is summed up together when calculating
    recursive stats.
    
    It's planned that the core stats will be moved to blkcg_gq, so we want
    to move the mechanism for keeping track of the stats of dead children
    from cfq to blkcg core.  This patch adds blkg_[rw]stat->aux_cnt which
    are atomic64_t's keeping track of auxiliary counts which are excluded
    when reading local counts but included for recursive.
    
    blkg_[rw]stat_merge() which were used by cfq to implement dead_stats
    are replaced by blkg_[rw]stat_add_aux(), and cfq now forwards stats of
    a dead cgroup to the aux counts of parent->stats instead of separate
    ->dead_stats.
    
    This will also help making blkg_[rw]stats per-cpu.
    Signed-off-by: default avatarTejun Heo <tj@kernel.org>
    Cc: Vivek Goyal <vgoyal@redhat.com>
    Signed-off-by: default avatarJens Axboe <axboe@fb.com>
    e6269c44
blk-cgroup.h 20.8 KB