dm cache: simplify the IDLE vs BUSY state calculation

Drop the MODERATE state since it wasn't buying us much.

Also, in check_migrations(), prepare for the next commit ("dm cache
policy smq: don't do any writebacks unless IDLE") by deferring to the
policy to make the final decision on whether writebacks can be
serviced.

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

diff --git a/drivers/md/dm-cache-target.c b/drivers/md/dm-cache-target.c
index 232078e..d682a05 100644 (file)
--- a/drivers/md/dm-cache-target.c
+++ b/drivers/md/dm-cache-target.c
@@ -1718,7 +1718,6 @@ static int invalidate_start(struct cache *cache, dm_cblock_t cblock,
 
 enum busy {
        IDLE,
-       MODERATE,
        BUSY
 };
 
@@ -1728,10 +1727,10 @@ static enum busy spare_migration_bandwidth(struct cache *cache)
        sector_t current_volume = (atomic_read(&cache->nr_io_migrations) + 1) *
                cache->sectors_per_block;
 
-       if (current_volume <= cache->migration_threshold)
-               return idle ? IDLE : MODERATE;
+       if (idle && current_volume <= cache->migration_threshold)
+               return IDLE;
        else
-               return idle ? MODERATE : BUSY;
+               return BUSY;
 }
 
 static void inc_hit_counter(struct cache *cache, struct bio *bio)
@@ -2047,8 +2046,6 @@ static void check_migrations(struct work_struct *ws)
 
        for (;;) {
                b = spare_migration_bandwidth(cache);
-               if (b == BUSY)
-                       break;
 
                r = policy_get_background_work(cache->policy, b == IDLE, &op);
                if (r == -ENODATA)