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authorTejun Heo2015-08-18 14:55:21 -0700
committerJens Axboe2015-08-18 15:49:17 -0700
commite6269c44546755094979ab53609e6e203a68c8ff (patch)
treefc083e47b6ea842e5d260084542a2ed5f76a86ea /Documentation/bcache.txt
parentae11889636111199dbcf47283b4167f578b69472 (diff)
blkcg: add blkg_[rw]stat->aux_cnt and replace cfq_group->dead_stats with it
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: Tejun Heo <tj@kernel.org> Cc: Vivek Goyal <vgoyal@redhat.com> Signed-off-by: Jens Axboe <axboe@fb.com>
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