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Commit 97658cdd authored by NeilBrown's avatar NeilBrown
Browse files

md: provide generic support for handling unplug callbacks. 



When an md device adds a request to a queue, it can call
mddev_check_plugged.
If this succeeds then we know that the md thread will be woken up
shortly, and ->plug_cnt will be non-zero until then, so some
processing can be delayed.

If it fails, then no unplug callback is expected and the make_request
function needs to do whatever is required to make the request happen.

Signed-off-by: default avatarNeilBrown <neilb@suse.de>
parent 482c0834

drivers/md/md.c

+56 −0
Original line number Diff line number Diff line
@@ -445,6 +445,61 @@ void md_flush_request(mddev_t *mddev, struct bio *bio) 
}

EXPORT_SYMBOL(md_flush_request);



/* Support for plugging.

 * This mirrors the plugging support in request_queue, but does not

 * require having a whole queue or request structures.

 * We allocate an md_plug_cb for each md device and each thread it gets

 * plugged on.  This links tot the private plug_handle structure in the

 * personality data where we keep a count of the number of outstanding

 * plugs so other code can see if a plug is active.

 */

struct md_plug_cb {

	struct blk_plug_cb cb;

	mddev_t *mddev;

};



static void plugger_unplug(struct blk_plug_cb *cb)

{

	struct md_plug_cb *mdcb = container_of(cb, struct md_plug_cb, cb);

	if (atomic_dec_and_test(&mdcb->mddev->plug_cnt))

		md_wakeup_thread(mdcb->mddev->thread);

	kfree(mdcb);

}



/* Check that an unplug wakeup will come shortly.

 * If not, wakeup the md thread immediately

 */

int mddev_check_plugged(mddev_t *mddev)

{

	struct blk_plug *plug = current->plug;

	struct md_plug_cb *mdcb;



	if (!plug)

		return 0;



	list_for_each_entry(mdcb, &plug->cb_list, cb.list) {

		if (mdcb->cb.callback == plugger_unplug &&

		    mdcb->mddev == mddev) {

			/* Already on the list, move to top */

			if (mdcb != list_first_entry(&plug->cb_list,

						    struct md_plug_cb,

						    cb.list))

				list_move(&mdcb->cb.list, &plug->cb_list);

			return 1;

		}

	}

	/* Not currently on the callback list */

	mdcb = kmalloc(sizeof(*mdcb), GFP_ATOMIC);

	if (!mdcb)

		return 0;



	mdcb->mddev = mddev;

	mdcb->cb.callback = plugger_unplug;

	atomic_inc(&mddev->plug_cnt);

	list_add(&mdcb->cb.list, &plug->cb_list);

	return 1;

}

EXPORT_SYMBOL_GPL(mddev_check_plugged);



static inline mddev_t *mddev_get(mddev_t *mddev)

{
@@ -494,6 +549,7 @@ void mddev_init(mddev_t *mddev) 
	atomic_set(&mddev->active, 1);

	atomic_set(&mddev->openers, 0);

	atomic_set(&mddev->active_io, 0);

	atomic_set(&mddev->plug_cnt, 0);

	spin_lock_init(&mddev->write_lock);

	atomic_set(&mddev->flush_pending, 0);

	init_waitqueue_head(&mddev->sb_wait);

drivers/md/md.h

+4 −0
Original line number Diff line number Diff line
@@ -179,6 +179,9 @@ struct mddev_s 
	int				delta_disks, new_level, new_layout;

	int				new_chunk_sectors;



	atomic_t			plug_cnt;	/* If device is expecting

							 * more bios soon.

							 */

	struct mdk_thread_s		*thread;	/* management thread */

	struct mdk_thread_s		*sync_thread;	/* doing resync or reconstruct */

	sector_t			curr_resync;	/* last block scheduled */
@@ -508,4 +511,5 @@ extern struct bio *bio_clone_mddev(struct bio *bio, gfp_t gfp_mask, 
				   mddev_t *mddev);

extern struct bio *bio_alloc_mddev(gfp_t gfp_mask, int nr_iovecs,

				   mddev_t *mddev);

extern int mddev_check_plugged(mddev_t *mddev);

#endif /* _MD_MD_H */