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Subject[PATCH RFC v4 09/13] virtio-mem: Offline and remove completely unplugged memory blocks
Date
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).

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>
---
drivers/virtio/virtio_mem.c | 47 +++++++++++++++++++++++++++++++++----
1 file changed, 43 insertions(+), 4 deletions(-)

diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c
index a12a0f9c076b..807d4e393427 100644
--- a/drivers/virtio/virtio_mem.c
+++ b/drivers/virtio/virtio_mem.c
@@ -436,6 +436,28 @@ 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.
*/
@@ -529,7 +551,13 @@ 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);
}

@@ -1275,7 +1303,8 @@ 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.
@@ -1331,9 +1360,19 @@ 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;
}

--
2.23.0
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