• David Hildenbrand's avatar
    virtio-mem: Paravirtualized memory hotunplug part 2 · 255f5985
    David Hildenbrand authored
    We also want to unplug online memory (contained in online memory blocks
    and, therefore, managed by the buddy), and eventually replug it later.
    
    When requested to unplug memory, we use alloc_contig_range() to allocate
    subblocks in online memory blocks (so we are the owner) and send them to
    our hypervisor. When requested to plug memory, we can replug such memory
    using free_contig_range() after asking our hypervisor.
    
    We also want to mark all allocated pages PG_offline, so nobody will
    touch them. To differentiate pages that were never onlined when
    onlining the memory block from pages allocated via alloc_contig_range(), we
    use PageDirty(). Based on this flag, virtio_mem_fake_online() can either
    online the pages for the first time or use free_contig_range().
    
    It is worth noting that there are no guarantees on how much memory can
    actually get unplugged again. All device memory might completely be
    fragmented with unmovable data, such that no subblock can get unplugged.
    
    We are not touching the ZONE_MOVABLE. If memory is onlined to the
    ZONE_MOVABLE, it can only get unplugged after that memory was offlined
    manually by user space. In normal operation, virtio-mem memory is
    suggested to be onlined to ZONE_NORMAL. In the future, we will try to
    make unplug more likely to succeed.
    
    Add a module parameter to control if online memory shall be touched.
    
    As we want to access alloc_contig_range()/free_contig_range() from
    kernel module context, export the symbols.
    
    Note: Whenever virtio-mem uses alloc_contig_range(), all affected pages
    are on the same node, in the same zone, and contain no holes.
    
    Acked-by: Michal Hocko <mhocko@suse.com> # to export contig range allocator API
    Tested-by: default avatarPankaj 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: Mel Gorman <mgorman@techsingularity.net>
    Cc: Mike Rapoport <rppt@linux.ibm.com>
    Cc: Alexander Duyck <alexander.h.duyck@linux.intel.com>
    Cc: Alexander Potapenko <glider@google.com>
    Signed-off-by: default avatarDavid Hildenbrand <david@redhat.com>
    Link: https://lore.kernel.org/r/20200507140139.17083-6-david@redhat.comSigned-off-by: default avatarMichael S. Tsirkin <mst@redhat.com>
    255f5985
virtio_mem.c 48.4 KB