dm mpath: reduce memory pressure when requeuing

When multipath needs to requeue I/O in the block layer the per-request
context shouldn't be allocated, as it will be freed immediately
afterwards anyway.  Avoiding this memory allocation will reduce memory
pressure during requeuing.

Signed-off-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Reviewed-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>

diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index 1c6a3f8da24d9a8e40716f018f5a6bdacb61eb99..2c2c33f249986c86e29c9633539e3636078579df 100644 (file)
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -378,12 +378,12 @@ static int __must_push_back(struct multipath *m)
 static int map_io(struct multipath *m, struct request *clone,
                  union map_info *map_context)
 {
-       int r = DM_MAPIO_REMAPPED;
+       int r = DM_MAPIO_REQUEUE;
        size_t nr_bytes = blk_rq_bytes(clone);
        unsigned long flags;
        struct pgpath *pgpath;
        struct block_device *bdev;
-       struct dm_mpath_io *mpio = map_context->ptr;
+       struct dm_mpath_io *mpio;
 
        spin_lock_irqsave(&m->lock, flags);
 
@@ -396,27 +396,29 @@ static int map_io(struct multipath *m, struct request *clone,
 
        if (pgpath) {
                if (pg_ready(m)) {
+                       if (set_mapinfo(m, map_context) < 0)
+                               /* ENOMEM, requeue */
+                               goto out_unlock;
+
                        bdev = pgpath->path.dev->bdev;
                        clone->q = bdev_get_queue(bdev);
                        clone->rq_disk = bdev->bd_disk;
+                       clone->cmd_flags |= REQ_FAILFAST_TRANSPORT;
+                       mpio = map_context->ptr;
                        mpio->pgpath = pgpath;
                        mpio->nr_bytes = nr_bytes;
                        if (pgpath->pg->ps.type->start_io)
                                pgpath->pg->ps.type->start_io(&pgpath->pg->ps,
                                                              &pgpath->path,
                                                              nr_bytes);
-               } else {
-                       __pg_init_all_paths(m);
-                       r = DM_MAPIO_REQUEUE;
+                       r = DM_MAPIO_REMAPPED;
+                       goto out_unlock;
                }
-       } else {
-               /* No path */
-               if (__must_push_back(m))
-                       r = DM_MAPIO_REQUEUE;
-               else
-                       r = -EIO;       /* Failed */
-       }
+               __pg_init_all_paths(m);
+       } else if (!__must_push_back(m))
+               r = -EIO;       /* Failed */
 
+out_unlock:
        spin_unlock_irqrestore(&m->lock, flags);
 
        return r;
@@ -912,19 +914,9 @@ static void multipath_dtr(struct dm_target *ti)
 static int multipath_map(struct dm_target *ti, struct request *clone,
                         union map_info *map_context)
 {
-       int r;
        struct multipath *m = (struct multipath *) ti->private;
 
-       if (set_mapinfo(m, map_context) < 0)
-               /* ENOMEM, requeue */
-               return DM_MAPIO_REQUEUE;
-
-       clone->cmd_flags |= REQ_FAILFAST_TRANSPORT;
-       r = map_io(m, clone, map_context);
-       if (r < 0 || r == DM_MAPIO_REQUEUE)
-               clear_mapinfo(m, map_context);
-
-       return r;
+       return map_io(m, clone, map_context);
 }
 
 /*