path: root/block
diff options
authorTejun Heo <tj@kernel.org>2012-03-05 13:15:27 -0800
committerJens Axboe <axboe@kernel.dk>2012-03-06 21:27:24 +0100
commit852c788f8365062c8a383c5a93f7f7289977cb50 (patch)
tree561b69e7f2b6bcc16de165b3b988990de7913615 /block
parentblock: add io_context->active_ref (diff)
block: implement bio_associate_current()
IO scheduling and cgroup are tied to the issuing task via io_context and cgroup of %current. Unfortunately, there are cases where IOs need to be routed via a different task which makes scheduling and cgroup limit enforcement applied completely incorrectly. For example, all bios delayed by blk-throttle end up being issued by a delayed work item and get assigned the io_context of the worker task which happens to serve the work item and dumped to the default block cgroup. This is double confusing as bios which aren't delayed end up in the correct cgroup and makes using blk-throttle and cfq propio together impossible. Any code which punts IO issuing to another task is affected which is getting more and more common (e.g. btrfs). As both io_context and cgroup are firmly tied to task including userland visible APIs to manipulate them, it makes a lot of sense to match up tasks to bios. This patch implements bio_associate_current() which associates the specified bio with %current. The bio will record the associated ioc and blkcg at that point and block layer will use the recorded ones regardless of which task actually ends up issuing the bio. bio release puts the associated ioc and blkcg. It grabs and remembers ioc and blkcg instead of the task itself because task may already be dead by the time the bio is issued making ioc and blkcg inaccessible and those are all block layer cares about. elevator_set_req_fn() is updated such that the bio elvdata is being allocated for is available to the elevator. This doesn't update block cgroup policies yet. Further patches will implement the support. -v2: #ifdef CONFIG_BLK_CGROUP added around bio->bi_ioc dereference in rq_ioc() to fix build breakage. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Vivek Goyal <vgoyal@redhat.com> Cc: Kent Overstreet <koverstreet@google.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block')
3 files changed, 30 insertions, 10 deletions
diff --git a/block/blk-core.c b/block/blk-core.c
index b2d0fcd8f87f..991c1d6ef245 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -696,7 +696,7 @@ static inline void blk_free_request(struct request_queue *q, struct request *rq)
static struct request *
-blk_alloc_request(struct request_queue *q, struct io_cq *icq,
+blk_alloc_request(struct request_queue *q, struct bio *bio, struct io_cq *icq,
unsigned int flags, gfp_t gfp_mask)
struct request *rq = mempool_alloc(q->rq.rq_pool, gfp_mask);
@@ -710,7 +710,7 @@ blk_alloc_request(struct request_queue *q, struct io_cq *icq,
if (flags & REQ_ELVPRIV) {
rq->elv.icq = icq;
- if (unlikely(elv_set_request(q, rq, gfp_mask))) {
+ if (unlikely(elv_set_request(q, rq, bio, gfp_mask))) {
mempool_free(rq, q->rq.rq_pool);
return NULL;
@@ -810,6 +810,22 @@ static bool blk_rq_should_init_elevator(struct bio *bio)
+ * rq_ioc - determine io_context for request allocation
+ * @bio: request being allocated is for this bio (can be %NULL)
+ *
+ * Determine io_context to use for request allocation for @bio. May return
+ * %NULL if %current->io_context doesn't exist.
+ */
+static struct io_context *rq_ioc(struct bio *bio)
+ if (bio && bio->bi_ioc)
+ return bio->bi_ioc;
+ return current->io_context;
* get_request - get a free request
* @q: request_queue to allocate request from
* @rw_flags: RW and SYNC flags
@@ -836,7 +852,7 @@ static struct request *get_request(struct request_queue *q, int rw_flags,
int may_queue;
et = q->elevator->type;
- ioc = current->io_context;
+ ioc = rq_ioc(bio);
if (unlikely(blk_queue_dead(q)))
return NULL;
@@ -919,14 +935,16 @@ retry:
/* create icq if missing */
if ((rw_flags & REQ_ELVPRIV) && unlikely(et->icq_cache && !icq)) {
- ioc = create_io_context(gfp_mask, q->node);
- if (ioc)
- icq = ioc_create_icq(ioc, q, gfp_mask);
+ create_io_context(gfp_mask, q->node);
+ ioc = rq_ioc(bio);
+ if (!ioc)
+ goto fail_alloc;
+ icq = ioc_create_icq(ioc, q, gfp_mask);
if (!icq)
goto fail_alloc;
- rq = blk_alloc_request(q, icq, rw_flags, gfp_mask);
+ rq = blk_alloc_request(q, bio, icq, rw_flags, gfp_mask);
if (unlikely(!rq))
goto fail_alloc;
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 9a4eac490e0b..abac87337d70 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -3299,7 +3299,8 @@ split_cfqq(struct cfq_io_cq *cic, struct cfq_queue *cfqq)
* Allocate cfq data structures associated with this request.
static int
-cfq_set_request(struct request_queue *q, struct request *rq, gfp_t gfp_mask)
+cfq_set_request(struct request_queue *q, struct request *rq, struct bio *bio,
+ gfp_t gfp_mask)
struct cfq_data *cfqd = q->elevator->elevator_data;
struct cfq_io_cq *cic = icq_to_cic(rq->elv.icq);
diff --git a/block/elevator.c b/block/elevator.c
index 451654fadab0..be3ab6df0fea 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -663,12 +663,13 @@ struct request *elv_former_request(struct request_queue *q, struct request *rq)
return NULL;
-int elv_set_request(struct request_queue *q, struct request *rq, gfp_t gfp_mask)
+int elv_set_request(struct request_queue *q, struct request *rq,
+ struct bio *bio, gfp_t gfp_mask)
struct elevator_queue *e = q->elevator;
if (e->type->ops.elevator_set_req_fn)
- return e->type->ops.elevator_set_req_fn(q, rq, gfp_mask);
+ return e->type->ops.elevator_set_req_fn(q, rq, bio, gfp_mask);
return 0;