dm cache: avoid preallocation if no work in writeback_some_dirty_blocks()

Refactor writeback_some_dirty_blocks() to avoid prealloc_data_structs()
if the policy doesn't have any dirty blocks ready for writeback.

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 c8a160b374120b02552101ca584843a6c75c42dd..408dd276d6c98d7ea3ae2d644142dfbe225658fb 100644 (file)
--- a/drivers/md/dm-cache-target.c
+++ b/drivers/md/dm-cache-target.c
@@ -2061,7 +2061,6 @@ static void process_deferred_writethrough_bios(struct cache *cache)
 
 static void writeback_some_dirty_blocks(struct cache *cache)
 {
-       int r = 0;
        dm_oblock_t oblock;
        dm_cblock_t cblock;
        struct prealloc structs;
@@ -2071,15 +2070,11 @@ static void writeback_some_dirty_blocks(struct cache *cache)
        memset(&structs, 0, sizeof(structs));
 
        while (spare_migration_bandwidth(cache)) {
-               if (prealloc_data_structs(cache, &structs))
-                       break;
-
-               r = policy_writeback_work(cache->policy, &oblock, &cblock, busy);
-               if (r)
-                       break;
+               if (policy_writeback_work(cache->policy, &oblock, &cblock, busy))
+                       break; /* no work to do */
 
-               r = get_cell(cache, oblock, &structs, &old_ocell);
-               if (r) {
+               if (prealloc_data_structs(cache, &structs) ||
+                   get_cell(cache, oblock, &structs, &old_ocell)) {
                        policy_set_dirty(cache->policy, oblock);
                        break;
                }