[PATCH v4 0/8] mm/memory_hotplug: Shrink zones before removing memory

[David Hildenbrand <david@redhat.com>]

This series fixes the access of uninitialized memmaps when shrinking
zones/nodes and when removing memory.

We stop trying to shrink ZONE_DEVICE, as it's buggy, fixing it would be
more involved (we don't have SECTION_IS_ONLINE as an indicator), and
shrinking is only of limited use (set_zone_contiguous() cannot detect
the ZONE_DEVICE as contiguous). As far as I can tell, this should be fine
for ZONE_DEVICE.

We continue shrinking zones, but I reduced the amount of code to a
minimum. Shrinking is especially necessary to keep zone->contiguous set
where possible, especially on memory unplug of DIMMs at zone boundaries.

--------------------------------------------------------------------------

Zones are now properly shrunk when offlining memory blocks or when
onlining failed. This allows to properly shrink zones on memory unplug
even if the separate memory blocks of a DIMM were onlined to different
zones or re-onlined to a different zone after offlining.

Example:

:/# cat /proc/zoneinfo
Node 1, zone  Movable
        spanned  0
        present  0
        managed  0
:/# echo "online_movable" > /sys/devices/system/memory/memory41/state
:/# echo "online_movable" > /sys/devices/system/memory/memory43/state
:/# cat /proc/zoneinfo
Node 1, zone  Movable
        spanned  98304
        present  65536
        managed  65536
:/# echo 0 > /sys/devices/system/memory/memory43/online
:/# cat /proc/zoneinfo
Node 1, zone  Movable
        spanned  32768
        present  32768
        managed  32768
:/# echo 0 > /sys/devices/system/memory/memory41/online
:/# cat /proc/zoneinfo
Node 1, zone  Movable
        spanned  0
        present  0
        managed  0

--------------------------------------------------------------------------

I tested this with DIMMs on x86, but didn't test the ZONE_DEVICE part yet.


v3 -> v4:
- Drop "mm/memremap: Get rid of memmap_init_zone_device()"
-- As Alexander noticed, it was messy either way :)
- Drop "mm/memory_hotplug: Exit early in __remove_pages() on BUGs"
- Drop "mm: Exit early in set_zone_contiguous() if already contiguous"
- Drop "mm/memory_hotplug: Optimize zone shrinking code when checking for
  holes"
- Merged "mm/memory_hotplug: Remove pages from a zone before removing
  memory" and "mm/memory_hotplug: Remove zone parameter from
  __remove_pages()" into "mm/memory_hotplug: Shrink zones when offlining
  memory"
- Added "mm/memory_hotplug: Poison memmap in remove_pfn_range_from_zone()"
- Stop shrinking ZONE_DEVICE
- Reshuffle patches, moving all fixes to the front. Add Fixes: tags.
- Change subject/description of various patches
- Minor changes (too many to mention)


Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Michal Hocko <mhocko@suse.com>


David Hildenbrand (8):
  mm/memory_hotplug: Don't access uninitialized memmaps in
    shrink_pgdat_span()
  mm/memory_hotplug: Don't access uninitialized memmaps in
    shrink_zone_span()
  mm/memory_hotplug: Shrink zones when offlining memory
  mm/memory_hotplug: Poison memmap in remove_pfn_range_from_zone()
  mm/memory_hotplug: We always have a zone in
    find_(smallest|biggest)_section_pfn
  mm/memory_hotplug: Don't check for "all holes" in shrink_zone_span()
  mm/memory_hotplug: Drop local variables in shrink_zone_span()
  mm/memory_hotplug: Cleanup __remove_pages()

 arch/arm64/mm/mmu.c            |   4 +-
 arch/ia64/mm/init.c            |   4 +-
 arch/powerpc/mm/mem.c          |   3 +-
 arch/s390/mm/init.c            |   4 +-
 arch/sh/mm/init.c              |   4 +-
 arch/x86/mm/init_32.c          |   4 +-
 arch/x86/mm/init_64.c          |   4 +-
 include/linux/memory_hotplug.h |   7 +-
 mm/memory_hotplug.c            | 184 +++++++++++----------------------
 mm/memremap.c                  |  10 +-
 10 files changed, 80 insertions(+), 148 deletions(-)

-- 
2.21.0