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![David Hildenbrand](/assets/img/avatar_default.png)
Each virtio-mem device owns exactly one memory region. It is responsible for adding/removing memory from that memory region on request. When the device driver starts up, the requested amount of memory is queried and then plugged to Linux. On request, further memory can be plugged or unplugged. This patch only implements the plugging part. On x86-64, memory can currently be plugged in 4MB ("subblock") granularity. When required, a new memory block will be added (e.g., usually 128MB on x86-64) in order to plug more subblocks. Only x86-64 was tested for now. The online_page callback is used to keep unplugged subblocks offline when onlining memory - similar to the Hyper-V balloon driver. Unplugged pages are marked PG_offline, to tell dump tools (e.g., makedumpfile) to skip them. User space is usually responsible for onlining the added memory. The memory hotplug notifier is used to synchronize virtio-mem activity against memory onlining/offlining. Each virtio-mem device can belong to a NUMA node, which allows us to easily add/remove small chunks of memory to/from a specific NUMA node by using multiple virtio-mem devices. Something that works even when the guest has no idea about the NUMA topology. One way to view virtio-mem is as a "resizable DIMM" or a DIMM with many "sub-DIMMS". This patch directly introduces the basic infrastructure to implement memory unplug. Especially the memory block states and subblock bitmaps will be heavily used there. Notes: - In case memory is to be onlined by user space, we limit the amount of offline memory blocks, to not run out of memory. This is esp. an issue if memory is added faster than it is getting onlined. - Suspend/Hibernate is not supported due to the way virtio-mem devices behave. Limited support might be possible in the future. - Reloading the device driver is not supported. Reviewed-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> Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net> Cc: Len Brown <lenb@kernel.org> Cc: linux-acpi@vger.kernel.org Signed-off-by: David Hildenbrand <david@redhat.com> Link: https://lore.kernel.org/r/20200507140139.17083-2-david@redhat.com Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
10 lines
462 B
Makefile
10 lines
462 B
Makefile
# SPDX-License-Identifier: GPL-2.0
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obj-$(CONFIG_VIRTIO) += virtio.o virtio_ring.o
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obj-$(CONFIG_VIRTIO_MMIO) += virtio_mmio.o
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obj-$(CONFIG_VIRTIO_PCI) += virtio_pci.o
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virtio_pci-y := virtio_pci_modern.o virtio_pci_common.o
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virtio_pci-$(CONFIG_VIRTIO_PCI_LEGACY) += virtio_pci_legacy.o
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obj-$(CONFIG_VIRTIO_BALLOON) += virtio_balloon.o
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obj-$(CONFIG_VIRTIO_INPUT) += virtio_input.o
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obj-$(CONFIG_VIRTIO_VDPA) += virtio_vdpa.o
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obj-$(CONFIG_VIRTIO_MEM) += virtio_mem.o
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