[Devel] [PATCH -mm v2 0/2] slab: cleanup mem hotplug synchronization

[Vladimir Davydov]

Hi,

kmem_cache_{create,destroy,shrink} need to get a stable value of
cpu/node online mask, because they init/destroy/access per-cpu/node
kmem_cache parts, which can be allocated or destroyed on cpu/mem
hotplug. To protect against cpu hotplug, these functions use
{get,put}_online_cpus. However, they do nothing to synchronize with
memory hotplug - taking the slab_mutex does not eliminate the
possibility of race as described in patch 2.

What we need there is something like get_online_cpus, but for memory. We
already have lock_memory_hotplug, which serves for the purpose, but it's
a bit of a hammer right now, because it's backed by a mutex. As a
result, it imposes some limitations to locking order, which are not
desirable, and can't be used just like get_online_cpus. That's why in
patch 1 I substitute it with get/put_online_mems, which work exactly
like get/put_online_cpus except they block not cpu, but memory hotplug.

[ v1 can be found at https://lkml.org/lkml/2014/4/6/68. I NAK'ed it by
myself, because it used an rw semaphore for get/put_online_mems, making
them dead lock prune. ]

Thanks,

Vladimir Davydov (2):
  mem-hotplug: implement get/put_online_mems
  slab: lock_memory_hotplug for kmem_cache_{create,destroy,shrink}

 include/linux/memory_hotplug.h |   14 ++--
 include/linux/mmzone.h         |    8 +--
 mm/kmemleak.c                  |    4 +-
 mm/memory-failure.c            |    8 +--
 mm/memory_hotplug.c            |  142 ++++++++++++++++++++++++++++------------
 mm/slab.c                      |   26 +-------
 mm/slab.h                      |    1 +
 mm/slab_common.c               |   35 +++++++++-
 mm/slob.c                      |    3 +-
 mm/slub.c                      |    9 ++-
 mm/vmscan.c                    |    2 +-
 11 files changed, 155 insertions(+), 97 deletions(-)

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1.7.10.4