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8947d7fc4e
We have some special RAM memory regions (managed by virtio-mem), whereby the guest agreed to only use selected memory ranges. "unused" parts are discarded so they won't consume memory - to logically unplug these memory ranges. Before the VM is allowed to use such logically unplugged memory again, coordination with the hypervisor is required. This results in "sparse" mmaps/RAMBlocks/memory regions, whereby only coordinated parts are valid to be used/accessed by the VM. In most cases, we don't care about that - e.g., in KVM, we simply have a single KVM memory slot. However, in case of vfio, registering the whole region with the kernel results in all pages getting pinned, and therefore an unexpected high memory consumption - discarding of RAM in that context is broken. Let's introduce a way to coordinate discarding/populating memory within a RAM memory region with such special consumers of RAM memory regions: they can register as listeners and get updates on memory getting discarded and populated. Using this machinery, vfio will be able to map only the currently populated parts, resulting in discarded parts not getting pinned and not consuming memory. A RamDiscardManager has to be set for a memory region before it is getting mapped, and cannot change while the memory region is mapped. Note: At some point, we might want to let RAMBlock users (esp. vfio used for nvme://) consume this interface as well. We'll need RAMBlock notifier calls when a RAMBlock is getting mapped/unmapped (via the corresponding memory region), so we can properly register a listener there as well. Reviewed-by: Pankaj Gupta <pankaj.gupta@cloud.ionos.com> Acked-by: Michael S. Tsirkin <mst@redhat.com> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: "Michael S. Tsirkin" <mst@redhat.com> Cc: Alex Williamson <alex.williamson@redhat.com> Cc: Dr. David Alan Gilbert <dgilbert@redhat.com> Cc: Igor Mammedov <imammedo@redhat.com> Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com> Cc: Peter Xu <peterx@redhat.com> Cc: Auger Eric <eric.auger@redhat.com> Cc: Wei Yang <richard.weiyang@linux.alibaba.com> Cc: teawater <teawaterz@linux.alibaba.com> Cc: Marek Kedzierski <mkedzier@redhat.com> Signed-off-by: David Hildenbrand <david@redhat.com> Message-Id: <20210413095531.25603-2-david@redhat.com> Signed-off-by: Eduardo Habkost <ehabkost@redhat.com> |
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