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authorNeilBrown <neilb@suse.de>2011-04-18 18:25:42 +1000
committerNeilBrown <neilb@suse.de>2011-04-18 18:25:42 +1000
commit97658cdd3af7d01461874c93b89afa4a2465e7c6 (patch)
treed4e2f930850eb3981307a3eec8c86399dcebf68a /drivers
parent482c083492ddaa32ef5864bae3d143dc8bcdf7d1 (diff)
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>
Diffstat (limited to 'drivers')
-rw-r--r--drivers/md/md.c56
-rw-r--r--drivers/md/md.h4
2 files changed, 60 insertions, 0 deletions
diff --git a/drivers/md/md.c b/drivers/md/md.c
index fb11170c717e..6e853c61d87e 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -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);
diff --git a/drivers/md/md.h b/drivers/md/md.h
index fad90228672f..0b1fd3f1d85b 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -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 */

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