On 31.07.20 11:18, David Hildenbrand wrote:
Grml, forgot to add cc: list for this patch, ccing the right people.
> virtio-mem adds memory in memory block granularity, to be able to
> remove it in the same granularity again later, and to grow slowly on
> demand. This, however, results in quite a lot of resources when
> adding a lot of memory. Resources are effectively stored in a list-based
> tree. Having a lot of resources not only wastes memory, it also makes
> traversing that tree more expensive, and makes /proc/iomem explode in
> size (e.g., requiring kexec-tools to manually merge resources later
> when e.g., trying to create a kdump header).
>
> Before this patch, we get (/proc/iomem) when hotplugging 2G via virtio-mem
> on x86-64:
> [...]
> 100000000-13fffffff : System RAM
> 140000000-33fffffff : virtio0
> 140000000-147ffffff : System RAM (virtio_mem)
> 148000000-14fffffff : System RAM (virtio_mem)
> 150000000-157ffffff : System RAM (virtio_mem)
> 158000000-15fffffff : System RAM (virtio_mem)
> 160000000-167ffffff : System RAM (virtio_mem)
> 168000000-16fffffff : System RAM (virtio_mem)
> 170000000-177ffffff : System RAM (virtio_mem)
> 178000000-17fffffff : System RAM (virtio_mem)
> 180000000-187ffffff : System RAM (virtio_mem)
> 188000000-18fffffff : System RAM (virtio_mem)
> 190000000-197ffffff : System RAM (virtio_mem)
> 198000000-19fffffff : System RAM (virtio_mem)
> 1a0000000-1a7ffffff : System RAM (virtio_mem)
> 1a8000000-1afffffff : System RAM (virtio_mem)
> 1b0000000-1b7ffffff : System RAM (virtio_mem)
> 1b8000000-1bfffffff : System RAM (virtio_mem)
> 3280000000-32ffffffff : PCI Bus 0000:00
>
> With this patch, we get (/proc/iomem):
> [...]
> fffc0000-ffffffff : Reserved
> 100000000-13fffffff : System RAM
> 140000000-33fffffff : virtio0
> 140000000-1bfffffff : System RAM (virtio_mem)
> 3280000000-32ffffffff : PCI Bus 0000:00
>
> Of course, with more hotplugged memory, it gets worse. When unplugging
> memory blocks again, try_remove_memory() (via
> offline_and_remove_memory()) will properly split the resource up again.
>
> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
> ---
> drivers/virtio/virtio_mem.c | 14 ++++++++++++--
> 1 file changed, 12 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c
> index f26f5f64ae822..2396a8d67875e 100644
> --- a/drivers/virtio/virtio_mem.c
> +++ b/drivers/virtio/virtio_mem.c
> @@ -415,6 +415,7 @@ static int virtio_mem_mb_add(struct virtio_mem *vm, unsigned long mb_id)
> {
> const uint64_t addr = virtio_mem_mb_id_to_phys(mb_id);
> int nid = vm->nid;
> + int rc;
>
> if (nid == NUMA_NO_NODE)
> nid = memory_add_physaddr_to_nid(addr);
> @@ -431,8 +432,17 @@ static int virtio_mem_mb_add(struct virtio_mem *vm, unsigned long mb_id)
> }
>
> dev_dbg(&vm->vdev->dev, "adding memory block: %lu\n", mb_id);
> - return add_memory_driver_managed(nid, addr, memory_block_size_bytes(),
> - vm->resource_name);
> + rc = add_memory_driver_managed(nid, addr, memory_block_size_bytes(),
> + vm->resource_name);
> + if (!rc) {
> + /*
> + * Try to reduce the number of resources by merging them. The
> + * memory removal path will properly split them up again.
> + */
> + merge_child_mem_resources(vm->parent_resource,
> + vm->resource_name);
> + }
> + return rc;
> }
>
> /*
>
--
Thanks,
David / dhildenb
