On Sat, Aug 08 2009 at 12:55am -0400,
Nikanth Karthikesan <knikanth@xxxxxxx> wrote:
> Export a way to delay initializing a request_queue after allocating it. This
> is needed by device-mapper devices, as they create the queue on device
> creation time, but they decide whether it would use the elevator and requests
> only after first successful table load. Only request-based dm-devices use the
> elevator and requests. Without this either one needs to initialize and free
> the mempool and elevator, if it was a bio-based dm-device or leave it
> allocated, as it is currently done.
>
> Signed-off-by: Nikanth Karthikesan <knikanth@xxxxxxx>
This patch needed to be refreshed to account for the changes from this
recent commit: a4e7d46407d73f35d217013b363b79a8f8eafcaa
I've attached a refreshed patch.
Though I still have questions/feedback below.
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 4b45435..5db0772 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -569,12 +571,25 @@ blk_init_queue_node(request_fn_proc *rfn, spinlock_t *lock, int node_id)
> if (!q)
> return NULL;
>
> - q->node = node_id;
> - if (blk_init_free_list(q)) {
> + if (blk_init_allocated_queue(q, rfn, lock)) {
> + blk_put_queue(q);
> kmem_cache_free(blk_requestq_cachep, q);
> return NULL;
> }
>
> + return q;
> +}
> +EXPORT_SYMBOL(blk_init_queue_node);
> +
> +int blk_init_allocated_queue(struct request_queue *q, request_fn_proc *rfn,
> + spinlock_t *lock)
> +{
> + int err = 0;
> +
> + err = blk_init_free_list(q);
> + if (err)
> + goto out;
> +
> /*
> * if caller didn't supply a lock, they get per-queue locking with
> * our embedded lock
> @@ -598,15 +613,20 @@ blk_init_queue_node(request_fn_proc *rfn, spinlock_t *lock, int node_id)
> /*
> * all done
> */
> - if (!elevator_init(q, NULL)) {
> - blk_queue_congestion_threshold(q);
> - return q;
> - }
> + err = elevator_init(q, NULL);
> + if (err)
> + goto free_and_out;
>
> - blk_put_queue(q);
> - return NULL;
> + blk_queue_congestion_threshold(q);
> +
> + return 0;
> +
> +free_and_out:
> + mempool_destroy(q->rq.rq_pool);
> +out:
> + return err;
> }
> -EXPORT_SYMBOL(blk_init_queue_node);
> +EXPORT_SYMBOL(blk_init_allocated_queue);
>
> int blk_get_queue(struct request_queue *q)
> {
In the previous code blk_init_queue_node() only called blk_put_queue()
iff elevator_init() failed.
Why is blk_init_queue_node() now always calling blk_put_queue() on an
error from blk_init_allocated_queue()? It could be that
blk_init_free_list() was what failed and not elevator_init().
I'd imagine it is because some callers of blk_init_allocated_queue(),
e.g. DM, must not have the queue's refcount dropped on failure? A
comment on _why_ would really help set the caller's expectations. Maybe
at the top of blk_init_allocated_queue()? E.g.:
"It is up to the caller to manage the allocated queue's lifecycle
relative to blk_init_allocated_queue() failure". I guess that is
obvious after having reviewed this but...
Also, a comment that blk_init_allocated_queue()'s mempool_destroy() is
to "cleanup the mempool allocated via blk_init_free_list()" would help.
Thanks,
Mike
Export a way to delay initializing a request_queue after allocating it. This
is needed by device-mapper devices, as they create the queue on device
creation time, but they decide whether it would use the elevator and requests
only after first successful table load. Only request-based dm-devices use the
elevator and requests. Without this either one needs to initialize and free
the mempool and elevator, if it was a bio-based dm-device or leave it
allocated, as it is currently done.
Signed-off-by: Nikanth Karthikesan <knikanth@xxxxxxx>
---
Index: linux-2.6/block/blk-core.c
===================================================================
--- linux-2.6.orig/block/blk-core.c
+++ linux-2.6/block/blk-core.c
@@ -495,6 +495,8 @@ struct request_queue *blk_alloc_queue_no
if (!q)
return NULL;
+ q->node = node_id;
+
q->backing_dev_info.unplug_io_fn = blk_backing_dev_unplug;
q->backing_dev_info.unplug_io_data = q;
q->backing_dev_info.ra_pages =
@@ -604,15 +606,20 @@ int blk_init_allocated_queue(struct requ
/*
* all done
*/
- if (!elevator_init(q, NULL)) {
- blk_queue_congestion_threshold(q);
- return q;
- }
+ err = elevator_init(q, NULL);
+ if (err)
+ goto free_and_out;
- blk_put_queue(q);
- return NULL;
+ blk_queue_congestion_threshold(q);
+
+ return 0;
+
+free_and_out:
+ mempool_destroy(q->rq.rq_pool);
+out:
+ return err;
}
-EXPORT_SYMBOL(blk_init_queue_node);
+EXPORT_SYMBOL(blk_init_allocated_queue);
int blk_get_queue(struct request_queue *q)
{
Index: linux-2.6/include/linux/blkdev.h
===================================================================
--- linux-2.6.orig/include/linux/blkdev.h
+++ linux-2.6/include/linux/blkdev.h
@@ -901,6 +901,8 @@ extern void blk_abort_queue(struct reque
extern struct request_queue *blk_init_queue_node(request_fn_proc *rfn,
spinlock_t *lock, int node_id);
extern struct request_queue *blk_init_queue(request_fn_proc *, spinlock_t *);
+extern int blk_init_allocated_queue(struct request_queue *q,
+ request_fn_proc *rfn, spinlock_t *lock);
extern void blk_cleanup_queue(struct request_queue *);
extern void blk_queue_make_request(struct request_queue *, make_request_fn *);
extern void blk_queue_bounce_limit(struct request_queue *, u64);
--
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