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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: NeilBrown <neilb@suse.de>
This commit is contained in:
NeilBrown 2011-04-18 18:25:42 +10:00
parent 482c083492
commit 97658cdd3a
2 changed files with 60 additions and 0 deletions
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56
drivers/md/md.c
View File

@ -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);

4
drivers/md/md.h
View File

@ -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 */