[v2,0/7] mm/memory_hotplug: selective merging of system ram resources

Message

David Hildenbrand Sept. 8, 2020, 8:10 p.m. UTC

Some add_memory*() users add memory in small, contiguous memory blocks.
Examples include virtio-mem, hyper-v balloon, and the XEN balloon.

This can quickly result in a lot of memory resources, whereby the actual
resource boundaries are not of interest (e.g., it might be relevant for
DIMMs, exposed via /proc/iomem to user space). We really want to merge
added resources in this scenario where possible.

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 when creating a kdump header. The
current kexec-tools resource count limit does not allow for more than
~100GB of memory with a memory block size of 128MB on x86-64).

Let's allow to selectively merge system ram resources by specifying a
new flag for add_memory*(). Patch #5 contains a /proc/iomem example. Only
tested with virtio-mem.

v1 -> v2:
- I had another look at v1 after vacation and didn't like it - it felt like
  a hack. So I want forward and added a proper flag to add_memory*(), and
  introduce a clean (non-racy) way to mark System RAM resources mergeable.
- "kernel/resource: move and rename IORESOURCE_MEM_DRIVER_MANAGED"
-- Clean that flag up, felt wrong in the PnP section
- "mm/memory_hotplug: prepare passing flags to add_memory() and friends"
-- Previously sent in other context - decided to keep Wei's ack
- "mm/memory_hotplug: MEMHP_MERGE_RESOURCE to specify merging of System
   RAM resources"
-- Cleaner approach to get the job done by using proper flags and only
   merging the single, specified resource
- "virtio-mem: try to merge system ram resources"
  "xen/balloon: try to merge system ram resources"
  "hv_balloon: try to merge system ram resources"
-- Use the new flag MEMHP_MERGE_RESOURCE, much cleaner

RFC -> v1:
- Switch from rather generic "merge_child_mem_resources()" where a resource
  name has to be specified to "merge_system_ram_resources().
- Smaller comment/documentation/patch description changes/fixes

David Hildenbrand (7):
  kernel/resource: make release_mem_region_adjustable() never fail
  kernel/resource: move and rename IORESOURCE_MEM_DRIVER_MANAGED
  mm/memory_hotplug: prepare passing flags to add_memory() and friends
  mm/memory_hotplug: MEMHP_MERGE_RESOURCE to specify merging of System
    RAM resources
  virtio-mem: try to merge system ram resources
  xen/balloon: try to merge system ram resources
  hv_balloon: try to merge system ram resources

 arch/powerpc/platforms/powernv/memtrace.c     |   2 +-
 .../platforms/pseries/hotplug-memory.c        |   2 +-
 drivers/acpi/acpi_memhotplug.c                |   2 +-
 drivers/base/memory.c                         |   2 +-
 drivers/dax/kmem.c                            |   2 +-
 drivers/hv/hv_balloon.c                       |   2 +-
 drivers/s390/char/sclp_cmd.c                  |   2 +-
 drivers/virtio/virtio_mem.c                   |   3 +-
 drivers/xen/balloon.c                         |   2 +-
 include/linux/ioport.h                        |  12 +-
 include/linux/memory_hotplug.h                |  19 ++-
 kernel/kexec_file.c                           |   2 +-
 kernel/resource.c                             | 109 ++++++++++++++----
 mm/memory_hotplug.c                           |  48 +++-----
 14 files changed, 141 insertions(+), 68 deletions(-)