[PATCH] dm snapshot: add workqueue

Add a workqueue so that I/O can be queued up to be flushed from a separate
thread (e.g.  if local interrupts are disabled).

A new per-snapshot spinlock pe_lock is introduced to protect queued_bios.

Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Mark McLoughlin <markmc@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index d929801..1c64854 100644 (file)
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -39,6 +39,9 @@
  */
 #define SNAPSHOT_PAGES 256
 
+struct workqueue_struct *ksnapd;
+static void flush_queued_bios(void *data);
+
 struct pending_exception {
        struct exception e;
 
@@ -488,6 +491,7 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
        s->active = 0;
        s->last_percent = 0;
        init_rwsem(&s->lock);
+       spin_lock_init(&s->pe_lock);
        s->table = ti->table;
 
        /* Allocate hash table for COW data */
@@ -523,6 +527,9 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
                goto bad6;
        }
 
+       bio_list_init(&s->queued_bios);
+       INIT_WORK(&s->queued_bios_work, flush_queued_bios, s);
+
        /* Add snapshot to the list of snapshots for this origin */
        /* Exceptions aren't triggered till snapshot_resume() is called */
        if (register_snapshot(s)) {
@@ -561,6 +568,8 @@ static void snapshot_dtr(struct dm_target *ti)
 {
        struct dm_snapshot *s = (struct dm_snapshot *) ti->private;
 
+       flush_workqueue(ksnapd);
+
        /* Prevent further origin writes from using this snapshot. */
        /* After this returns there can be no new kcopyd jobs. */
        unregister_snapshot(s);
@@ -594,6 +603,19 @@ static void flush_bios(struct bio *bio)
        }
 }
 
+static void flush_queued_bios(void *data)
+{
+       struct dm_snapshot *s = (struct dm_snapshot *) data;
+       struct bio *queued_bios;
+       unsigned long flags;
+
+       spin_lock_irqsave(&s->pe_lock, flags);
+       queued_bios = bio_list_get(&s->queued_bios);
+       spin_unlock_irqrestore(&s->pe_lock, flags);
+
+       flush_bios(queued_bios);
+}
+
 /*
  * Error a list of buffers.
  */
@@ -1240,8 +1262,17 @@ static int __init dm_snapshot_init(void)
                goto bad5;
        }
 
+       ksnapd = create_singlethread_workqueue("ksnapd");
+       if (!ksnapd) {
+               DMERR("Failed to create ksnapd workqueue.");
+               r = -ENOMEM;
+               goto bad6;
+       }
+
        return 0;
 
+      bad6:
+       mempool_destroy(pending_pool);
       bad5:
        kmem_cache_destroy(pending_cache);
       bad4:
@@ -1259,6 +1290,8 @@ static void __exit dm_snapshot_exit(void)
 {
        int r;
 
+       destroy_workqueue(ksnapd);
+
        r = dm_unregister_target(&snapshot_target);
        if (r)
                DMERR("snapshot unregister failed %d", r);

diff --git a/drivers/md/dm-snap.h b/drivers/md/dm-snap.h
index 221eb88..15fa2ae 100644 (file)
--- a/drivers/md/dm-snap.h
+++ b/drivers/md/dm-snap.h
@@ -10,7 +10,9 @@
 #define DM_SNAPSHOT_H
 
 #include "dm.h"
+#include "dm-bio-list.h"
 #include <linux/blkdev.h>
+#include <linux/workqueue.h>
 
 struct exception_table {
        uint32_t hash_mask;
@@ -112,10 +114,20 @@ struct dm_snapshot {
        struct exception_table pending;
        struct exception_table complete;
 
+       /*
+        * pe_lock protects all pending_exception operations and access
+        * as well as the snapshot_bios list.
+        */
+       spinlock_t pe_lock;
+
        /* The on disk metadata handler */
        struct exception_store store;
 
        struct kcopyd_client *kcopyd_client;
+
+       /* Queue of snapshot writes for ksnapd to flush */
+       struct bio_list queued_bios;
+       struct work_struct queued_bios_work;
 };
 
 /*