md: incorporate new plugging into raid5.

In raid5 plugging is used for 2 things:
 1/ collecting writes that require a bitmap update
 2/ collecting writes in the hope that we can create full
    stripes - or at least more-full.

We now release these different sets of stripes when plug_cnt
is zero.

Also in make_request, we call mddev_check_plug to hopefully increase
plug_cnt, and wake up the thread at the end if plugging wasn't
achieved for some reason.

Signed-off-by: NeilBrown <neilb@suse.de>

1 files changed, 16 insertions, 7 deletions

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index a1755a6a3e5f..f301e6ae220c 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -27,12 +27,12 @@
  *
  * We group bitmap updates into batches.  Each batch has a number.
  * We may write out several batches at once, but that isn't very important.
- * conf->bm_write is the number of the last batch successfully written.
- * conf->bm_flush is the number of the last batch that was closed to
+ * conf->seq_write is the number of the last batch successfully written.
+ * conf->seq_flush is the number of the last batch that was closed to
  *    new additions.
  * When we discover that we will need to write to any block in a stripe
  * (in add_stripe_bio) we update the in-memory bitmap and record in sh->bm_seq
- * the number of the batch it will be in. This is bm_flush+1.
+ * the number of the batch it will be in. This is seq_flush+1.
  * When we are ready to do a write, if that batch hasn't been written yet,
  *   we plug the array and queue the stripe for later.
  * When an unplug happens, we increment bm_flush, thus closing the current
@@ -459,7 +459,7 @@ get_active_stripe(raid5_conf_t *conf, sector_t sector,
                                                      < (conf->max_nr_stripes *3/4)
                                                      || !conf->inactive_blocked),
                                                     conf->device_lock,
-                                                    md_wakeup_thread(conf->mddev->thread));
+                                                    );
                                 conf->inactive_blocked = 0;
                         } else
                                 init_stripe(sh, sector, previous);
@@ -3927,6 +3927,7 @@ static int make_request(mddev_t *mddev, struct bio * bi)
         struct stripe_head *sh;
         const int rw = bio_data_dir(bi);
         int remaining;
+        int plugged;
 
         if (unlikely(bi->bi_rw & REQ_FLUSH)) {
                 md_flush_request(mddev, bi);
@@ -3945,6 +3946,7 @@ static int make_request(mddev_t *mddev, struct bio * bi)
         bi->bi_next = NULL;
         bi->bi_phys_segments = 1;       /* over-loaded to count active stripes */
 
+        plugged = mddev_check_plugged(mddev);
         for (;logical_sector < last_sector; logical_sector += STRIPE_SECTORS) {
                 DEFINE_WAIT(w);
                 int disks, data_disks;
@@ -4059,6 +4061,9 @@ static int make_request(mddev_t *mddev, struct bio * bi)
                 }
                         
         }
+        if (!plugged)
+                md_wakeup_thread(mddev->thread);
+
         spin_lock_irq(&conf->device_lock);
         remaining = raid5_dec_bi_phys_segments(bi);
         spin_unlock_irq(&conf->device_lock);
@@ -4472,14 +4477,18 @@ static void raid5d(mddev_t *mddev)
         while (1) {
                 struct bio *bio;
 
-                if (conf->seq_flush != conf->seq_write) {
-                        int seq = conf->seq_flush;
+                if (atomic_read(&mddev->plug_cnt) == 0 &&
+                    !list_empty(&conf->bitmap_list)) {
+                        /* Now is a good time to flush some bitmap updates */
+                        conf->seq_flush++;
                         spin_unlock_irq(&conf->device_lock);
                         bitmap_unplug(mddev->bitmap);
                         spin_lock_irq(&conf->device_lock);
-                        conf->seq_write = seq;
+                        conf->seq_write = conf->seq_flush;
                         activate_bit_delay(conf);
                 }
+                if (atomic_read(&mddev->plug_cnt) == 0)
+                        raid5_activate_delayed(conf);
 
                 while ((bio = remove_bio_from_retry(conf))) {
                         int ok;