virtio-mem: Offline and remove completely unplugged memory blocks

Let's offline+remove memory blocks once all subblocks are unplugged. We
can use the new Linux MM interface for that. As no memory is in use
anymore, this shouldn't take a long time and shouldn't fail. There might
be corner cases where the offlining could still fail (especially, if
another notifier NACKs the offlining request).

Acked-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Tested-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: David Hildenbrand <david@redhat.com>
Link: https://lore.kernel.org/r/20200507140139.17083-10-david@redhat.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c
index b0b41c73ce89e2542d8e6ff07d59af307fb33b49..a2edb87e5ed8641460e513c3028167c0328f7ba3 100644 (file)
--- a/drivers/virtio/virtio_mem.c
+++ b/drivers/virtio/virtio_mem.c
@@ -446,6 +446,28 @@ static int virtio_mem_mb_remove(struct virtio_mem *vm, unsigned long mb_id)
        return remove_memory(nid, addr, memory_block_size_bytes());
 }
 
+/*
+ * Try to offline and remove a memory block from Linux.
+ *
+ * Must not be called with the vm->hotplug_mutex held (possible deadlock with
+ * onlining code).
+ *
+ * Will not modify the state of the memory block.
+ */
+static int virtio_mem_mb_offline_and_remove(struct virtio_mem *vm,
+                                           unsigned long mb_id)
+{
+       const uint64_t addr = virtio_mem_mb_id_to_phys(mb_id);
+       int nid = vm->nid;
+
+       if (nid == NUMA_NO_NODE)
+               nid = memory_add_physaddr_to_nid(addr);
+
+       dev_dbg(&vm->vdev->dev, "offlining and removing memory block: %lu\n",
+               mb_id);
+       return offline_and_remove_memory(nid, addr, memory_block_size_bytes());
+}
+
 /*
  * Trigger the workqueue so the device can perform its magic.
  */
@@ -537,7 +559,13 @@ static void virtio_mem_notify_offline(struct virtio_mem *vm,
                break;
        }
 
-       /* trigger the workqueue, maybe we can now unplug memory. */
+       /*
+        * Trigger the workqueue, maybe we can now unplug memory. Also,
+        * when we offline and remove a memory block, this will re-trigger
+        * us immediately - which is often nice because the removal of
+        * the memory block (e.g., memmap) might have freed up memory
+        * on other memory blocks we manage.
+        */
        virtio_mem_retry(vm);
 }
 
@@ -1284,7 +1312,8 @@ static int virtio_mem_mb_unplug_any_sb_offline(struct virtio_mem *vm,
  * Unplug the desired number of plugged subblocks of an online memory block.
  * Will skip subblock that are busy.
  *
- * Will modify the state of the memory block.
+ * Will modify the state of the memory block. Might temporarily drop the
+ * hotplug_mutex.
  *
  * Note: Can fail after some subblocks were successfully unplugged. Can
  *       return 0 even if subblocks were busy and could not get unplugged.
@@ -1340,9 +1369,19 @@ static int virtio_mem_mb_unplug_any_sb_online(struct virtio_mem *vm,
        }
 
        /*
-        * TODO: Once all subblocks of a memory block were unplugged, we want
-        * to offline the memory block and remove it.
+        * Once all subblocks of a memory block were unplugged, offline and
+        * remove it. This will usually not fail, as no memory is in use
+        * anymore - however some other notifiers might NACK the request.
         */
+       if (virtio_mem_mb_test_sb_unplugged(vm, mb_id, 0, vm->nb_sb_per_mb)) {
+               mutex_unlock(&vm->hotplug_mutex);
+               rc = virtio_mem_mb_offline_and_remove(vm, mb_id);
+               mutex_lock(&vm->hotplug_mutex);
+               if (!rc)
+                       virtio_mem_mb_set_state(vm, mb_id,
+                                               VIRTIO_MEM_MB_STATE_UNUSED);
+       }
+
        return 0;
 }