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SubjectRe: [PATCH v2 08/10] 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).
>
> 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 35f20232770c..aa322e7732a4 100644
> --- a/drivers/virtio/virtio_mem.c
> +++ b/drivers/virtio/virtio_mem.c
> @@ -443,6 +443,28 @@ 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.
> */
> @@ -535,7 +557,13 @@ 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);
> }
>
> @@ -1282,7 +1310,8 @@ 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.
> @@ -1338,9 +1367,19 @@ 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;
> }
>

Acked-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>

> --

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