[PATCH v1 09/29] virtio-mem: don't always trigger the workqueue when offlining memory

[David Hildenbrand <david@redhat.com>]

Let's trigger from offlining code when we're not allowed to touch online
memory.

Handle the other case (memmap possibly freeing up another memory block)
when actually removing memory. When removing via virtio_mem_remove(),
virtio_mem_retry() is a NOP and safe to use.

While at it, move retry handling when offlining out of
virtio_mem_notify_offline(), to share it with Device Block Mode (DBM)
soon.

Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 drivers/virtio/virtio_mem.c | 40 ++++++++++++++++++++++++++-----------
 1 file changed, 28 insertions(+), 12 deletions(-)

diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c
index 5c93f8a65eba..8ea00f0b2ecd 100644
--- a/drivers/virtio/virtio_mem.c
+++ b/drivers/virtio/virtio_mem.c
@@ -158,6 +158,7 @@ static DEFINE_MUTEX(virtio_mem_mutex);
 static LIST_HEAD(virtio_mem_devices);
 
 static void virtio_mem_online_page_cb(struct page *page, unsigned int order);
+static void virtio_mem_retry(struct virtio_mem *vm);
 
 /*
  * Register a virtio-mem device so it will be considered for the online_page
@@ -435,9 +436,17 @@ static int virtio_mem_mb_add(struct virtio_mem *vm, unsigned long mb_id)
 static int virtio_mem_mb_remove(struct virtio_mem *vm, unsigned long mb_id)
 {
 	const uint64_t addr = virtio_mem_mb_id_to_phys(mb_id);
+	int rc;
 
 	dev_dbg(&vm->vdev->dev, "removing memory block: %lu\n", mb_id);
-	return remove_memory(vm->nid, addr, memory_block_size_bytes());
+	rc = remove_memory(vm->nid, addr, memory_block_size_bytes());
+	if (!rc)
+		/*
+		 * We might have freed up memory we can now unplug, retry
+		 * immediately instead of waiting.
+		 */
+		virtio_mem_retry(vm);
+	return rc;
 }
 
 /*
@@ -452,11 +461,19 @@ 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 rc;
 
 	dev_dbg(&vm->vdev->dev, "offlining and removing memory block: %lu\n",
 		mb_id);
-	return offline_and_remove_memory(vm->nid, addr,
-					 memory_block_size_bytes());
+	rc = offline_and_remove_memory(vm->nid, addr,
+				       memory_block_size_bytes());
+	if (!rc)
+		/*
+		 * We might have freed up memory we can now unplug, retry
+		 * immediately instead of waiting.
+		 */
+		virtio_mem_retry(vm);
+	return rc;
 }
 
 /*
@@ -534,15 +551,6 @@ static void virtio_mem_notify_offline(struct virtio_mem *vm,
 		BUG();
 		break;
 	}
-
-	/*
-	 * 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);
 }
 
 static void virtio_mem_notify_online(struct virtio_mem *vm, unsigned long mb_id)
@@ -679,6 +687,14 @@ static int virtio_mem_memory_notifier_cb(struct notifier_block *nb,
 		break;
 	case MEM_OFFLINE:
 		virtio_mem_notify_offline(vm, mb_id);
+
+		/*
+		 * Trigger the workqueue. Now that we have some offline memory,
+		 * maybe we can handle pending unplug requests.
+		 */
+		if (!unplug_online)
+			virtio_mem_retry(vm);
+
 		vm->hotplug_active = false;
 		mutex_unlock(&vm->hotplug_mutex);
 		break;
-- 
2.26.2