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>

1 files changed, 15 insertions, 23 deletions

diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index 1c6a3f8da24d..2c2c33f24998 100644
--- 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);
 }
 
 /*