dm: move deferred bio flushing to workqueue

Add a single-thread workqueue for each mapped device
and move flushing of the lists of pushback and deferred bios
to this new workqueue.

Signed-off-by: Milan Broz <mbroz@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

1 files changed, 67 insertions, 12 deletions

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 9ca012e639a8..6617ce4af095 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -71,6 +71,19 @@ union map_info *dm_get_mapinfo(struct bio *bio)
 #define DMF_DELETING 4
 #define DMF_NOFLUSH_SUSPENDING 5
 
+/*
+ * Work processed by per-device workqueue.
+ */
+struct dm_wq_req {
+        enum {
+                DM_WQ_FLUSH_ALL,
+                DM_WQ_FLUSH_DEFERRED,
+        } type;
+        struct work_struct work;
+        struct mapped_device *md;
+        void *context;
+};
+
 struct mapped_device {
         struct rw_semaphore io_lock;
         struct mutex suspend_lock;
@@ -96,6 +109,11 @@ struct mapped_device {
         struct bio_list pushback;
 
         /*
+         * Processing queue (flush/barriers)
+         */
+        struct workqueue_struct *wq;
+
+        /*
          * The current mapping.
          */
         struct dm_table *map;
@@ -1044,6 +1062,10 @@ static struct mapped_device *alloc_dev(int minor)
         add_disk(md->disk);
         format_dev_t(md->name, MKDEV(_major, minor));
 
+        md->wq = create_singlethread_workqueue("kdmflush");
+        if (!md->wq)
+                goto bad_thread;
+
         /* Populate the mapping, nobody knows we exist yet */
         spin_lock(&_minor_lock);
         old_md = idr_replace(&_minor_idr, md, minor);
@@ -1053,6 +1075,8 @@ static struct mapped_device *alloc_dev(int minor)
 
         return md;
 
+bad_thread:
+        put_disk(md->disk);
 bad_disk:
         bioset_free(md->bs);
 bad_no_bioset:
@@ -1080,6 +1104,7 @@ static void free_dev(struct mapped_device *md)
                 unlock_fs(md);
                 bdput(md->suspended_bdev);
         }
+        destroy_workqueue(md->wq);
         mempool_destroy(md->tio_pool);
         mempool_destroy(md->io_pool);
         bioset_free(md->bs);
@@ -1308,6 +1333,44 @@ static void __merge_pushback_list(struct mapped_device *md)
         spin_unlock_irqrestore(&md->pushback_lock, flags);
 }
 
+static void dm_wq_work(struct work_struct *work)
+{
+        struct dm_wq_req *req = container_of(work, struct dm_wq_req, work);
+        struct mapped_device *md = req->md;
+
+        down_write(&md->io_lock);
+        switch (req->type) {
+        case DM_WQ_FLUSH_ALL:
+                __merge_pushback_list(md);
+                /* pass through */
+        case DM_WQ_FLUSH_DEFERRED:
+                __flush_deferred_io(md);
+                break;
+        default:
+                DMERR("dm_wq_work: unrecognised work type %d", req->type);
+                BUG();
+        }
+        up_write(&md->io_lock);
+}
+
+static void dm_wq_queue(struct mapped_device *md, int type, void *context,
+                        struct dm_wq_req *req)
+{
+        req->type = type;
+        req->md = md;
+        req->context = context;
+        INIT_WORK(&req->work, dm_wq_work);
+        queue_work(md->wq, &req->work);
+}
+
+static void dm_queue_flush(struct mapped_device *md, int type, void *context)
+{
+        struct dm_wq_req req;
+
+        dm_wq_queue(md, type, context, &req);
+        flush_workqueue(md->wq);
+}
+
 /*
  * Swap in a new table (destroying old one).
  */
@@ -1450,9 +1513,7 @@ int dm_suspend(struct mapped_device *md, unsigned suspend_flags)
 
         /* were we interrupted ? */
         if (r < 0) {
-                down_write(&md->io_lock);
-                __flush_deferred_io(md);
-                up_write(&md->io_lock);
+                dm_queue_flush(md, DM_WQ_FLUSH_DEFERRED, NULL);
 
                 unlock_fs(md);
                 goto out; /* pushback list is already flushed, so skip flush */
@@ -1463,16 +1524,12 @@ int dm_suspend(struct mapped_device *md, unsigned suspend_flags)
         set_bit(DMF_SUSPENDED, &md->flags);
 
 flush_and_out:
-        if (r && noflush) {
+        if (r && noflush)
                 /*
                  * Because there may be already I/Os in the pushback list,
                  * flush them before return.
                  */
-                down_write(&md->io_lock);
-                __merge_pushback_list(md);
-                __flush_deferred_io(md);
-                up_write(&md->io_lock);
-        }
+                dm_queue_flush(md, DM_WQ_FLUSH_ALL, NULL);
 
 out:
         if (r && md->suspended_bdev) {
@@ -1504,9 +1561,7 @@ int dm_resume(struct mapped_device *md)
         if (r)
                 goto out;
 
-        down_write(&md->io_lock);
-        __flush_deferred_io(md);
-        up_write(&md->io_lock);
+        dm_queue_flush(md, DM_WQ_FLUSH_DEFERRED, NULL);
 
         unlock_fs(md);