blkcg: replace blkcg_policy->pd_size with ->pd_alloc/free_fn() methods

A blkg (blkcg_gq) represents the relationship between a cgroup and
request_queue.  Each active policy has a pd (blkg_policy_data) on each
blkg.  The pd's were allocated by blkcg core and each policy could
request to allocate extra space at the end by setting
blkcg_policy->pd_size larger than the size of pd.

This is a bit unusual but was done this way mostly to simplify error
handling and all the existing use cases could be handled this way;
however, this is becoming too restrictive now that percpu memory can
be allocated without blocking.

This introduces two new mandatory blkcg_policy methods - pd_alloc_fn()
and pd_free_fn() - which are used to allocate and release pd for a
given policy.  As pd allocation is now done from policy side, it can
simply allocate a larger area which embeds pd at the beginning.  This
change makes ->pd_size pointless.  Removed.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 12 insertions, 1 deletions

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index b23193518ac7..f1dd691c5359 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -403,6 +403,11 @@ static void throtl_service_queue_exit(struct throtl_service_queue *sq)
         del_timer_sync(&sq->pending_timer);
 }
 
+static struct blkg_policy_data *throtl_pd_alloc(gfp_t gfp, int node)
+{
+        return kzalloc_node(sizeof(struct throtl_grp), gfp, node);
+}
+
 static void throtl_pd_init(struct blkcg_gq *blkg)
 {
         struct throtl_grp *tg = blkg_to_tg(blkg);
@@ -493,6 +498,11 @@ static void throtl_pd_exit(struct blkcg_gq *blkg)
         throtl_service_queue_exit(&tg->service_queue);
 }
 
+static void throtl_pd_free(struct blkg_policy_data *pd)
+{
+        kfree(pd);
+}
+
 static void throtl_pd_reset_stats(struct blkcg_gq *blkg)
 {
         struct throtl_grp *tg = blkg_to_tg(blkg);
@@ -1468,12 +1478,13 @@ static void throtl_shutdown_wq(struct request_queue *q)
 }
 
 static struct blkcg_policy blkcg_policy_throtl = {
-        .pd_size                = sizeof(struct throtl_grp),
         .cftypes                = throtl_files,
 
+        .pd_alloc_fn            = throtl_pd_alloc,
         .pd_init_fn             = throtl_pd_init,
         .pd_online_fn           = throtl_pd_online,
         .pd_exit_fn             = throtl_pd_exit,
+        .pd_free_fn             = throtl_pd_free,
         .pd_reset_stats_fn      = throtl_pd_reset_stats,
 };