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    Subject[RFC PATCH v3 00/31] Dynamic NUMA: Runtime NUMA memory layout reconfiguration
    Date
    There is still some cleanup to do, so I'm just posting these early and often. I
    would appreciate some review to make sure that the basic approaches are sound,
    and especially suggestions regarding TODO #1 below. If everything goes well,
    I'd like to seem them merged circa 3.12.

    --

    These patches allow the NUMA memory layout (meaning which node each physical
    page belongs to, the mapping from physical pages to NUMA nodes) to be changed
    at runtime in place (without hotplugging).

    TODO:

    1) Currently, I use pageflag setters without "owning" pages which could cause
    loss of pageflag updates when combined with non-atomic pageflag users in
    mm/*. Some options for solving this: (a) make all pageflags access atomic,
    (b) use pageblock flags, (c) use bits in a new bitmap, or (d) attempt to work
    around races in a similar way to memory-failure.

    2) Fix inaccurate accounting in some cases. Example:
    ## "5 MB" should be ~"42 MB"
    # dnuma-test s 0 2 128
    # numactl --hardware
    available: 4 nodes (0-3)
    node 0 cpus: 0
    node 0 size: 43 MB
    node 0 free: 11 MB
    node 1 cpus:
    node 1 size: 5 MB
    node 1 free: 34 MB
    node 2 cpus:
    node 2 size: 42 MB
    node 2 free: 28 MB
    node 3 cpus:
    node 3 size: 0 MB
    node 3 free: 0 MB

    = Why/when is this useful? =

    In virtual machines (VMs) running on NUMA systems both [a] if/when the
    hypervisor decides to move their backing memory around (compacting,
    prioritizing another VMs desired layout, etc) and [b] in general for
    migration of VMs.

    The hardware is _already_ changing the NUMA layout underneath us. We have
    powerpc64 systems with firmware that currently move the backing memory around,
    and have the ability to notify Linux of new NUMA info.

    = How are you managing to do this? =

    Reconfiguration of page->node mappings is done at the page allocator
    level by both pulling free pages out of the free lists (when a new memory
    layout is committed) & redirecting pages on free to their new node.

    Because we can't change page_node(A) while A is allocated [1], a rbtree
    holding the mapping from pfn ranges to node ids ('struct memlayout')
    is introduced to track the pfn->node mapping for
    yet-to-be-transplanted pages. A lookup in this rbtree occurs on any
    page allocator path that decides which zone to free a page to.

    To avoid horrible performance due to rbtree lookups all the time, the
    rbtree is only consulted when the page is marked with a new pageflag
    (LookupNode).

    [1]: quite a few users of page_node() depend on it not changing, some
    accumulate per-node stats by using this. We'd also have to change it via atomic
    operations to avoid disturbing the pageflags which share the same unsigned
    long.

    = Code & testing =

    A debugfs interface allows the NUMA memory layout to be changed. Basically,
    you don't need to have weird systems to test this, in fact, I've done all my
    testing so far in plain old qemu-i386 & qemu-x86_64.

    A script which stripes the memory between nodes or pushes all memory to a
    (potentially new) node is avaliable here:

    https://raw.github.com/jmesmon/trifles/master/bin/dnuma-test

    The patches are also available via:

    https://github.com/jmesmon/linux.git dnuma/v36

    2325de5^..e0f8f35

    = Current Limitations =

    For the reconfiguration to be effective (and not make the allocator make
    poorer choices), updating the cpu->node mappings is also needed. This patchset
    does _not_ handle this. Also missing is a way to update topology (node
    distances), which is slightly less fatal.

    These patches only work on SPARSEMEM and the node id _must_ fit in the pageflags
    (can't be pushed out to the section). This generally means that 32-bit
    platforms are out (unless you hack MAX_PHYS{ADDR,MEM}_BITS).

    This code does the reconfiguration without hotplugging memory at all (1
    errant page doesn't keep us from fixing the rest of them). But it still
    depends on MEMORY_HOTPLUG for functions that online nodes & adjust
    zone/pgdat size.

    Things that need doing or would be nice to have but aren't bugs:

    - While the interface is meant to be driven via a hypervisor/firmware, that
    portion is not yet included.
    - notifier for kernel users of memory that need/want their allocations on a
    particular node (NODE_DATA(), for instance).
    - notifier for userspace.
    - a way to allocate things from the appropriate node prior to the page
    allocator being fully updated (could just be "allocate it wrong now &
    reallocate later").
    - Make memlayout faster (potentially via per-node allocation, different data
    structure, and/or more/smarter caching).
    - Propagation of updated layout knowledge into kmem_caches (SL*B).

    --

    Since v2: http://comments.gmane.org/gmane.linux.kernel.mm/98371

    - update sysfs node->memory region mappings when a reconfiguration occurs
    - fixup locking when updating node_spanned_pages.
    - rework memlayout api for use by sysfs refresh code
    - remove holes for memlayouts to make iteration over them less of a chore.

    Since v1: http://comments.gmane.org/gmane.linux.kernel.mm/95541

    - Update watermarks.
    - Update zone percpu pageset ->batch & ->high only when needed.
    - Don't lazily adjust {pgdat,zone}->{present_pages,managed_pages}, set them all at once.
    - Don't attempt to use more than nr_node_ids nodes.

    --


    Cody P Schafer (31):
    rbtree: add postorder iteration functions.
    rbtree: add rbtree_postorder_for_each_entry_safe() helper.
    mm/memory_hotplug: factor out zone+pgdat growth.
    memory_hotplug: export ensure_zone_is_initialized() in mm/internal.h
    mm/memory_hotplug: use {pgdat,zone}_is_empty() when resizing zones &
    pgdats
    mm: add nid_zone() helper
    mm: Add Dynamic NUMA Kconfig.
    page_alloc: add return_pages_to_zone() when DYNAMIC_NUMA is enabled.
    page_alloc: in move_freepages(), skip pages instead of VM_BUG on node
    differences.
    page_alloc: when dynamic numa is enabled, don't check that all pages
    in a block belong to the same zone
    page-flags dnuma: reserve a pageflag for determining if a page needs a
    node lookup.
    memory_hotplug: factor out locks in mem_online_cpu()
    mm: add memlayout & dnuma to track pfn->nid & transplant pages between
    nodes
    mm: memlayout+dnuma: add debugfs interface
    drivers/base/memory.c: alphabetize headers.
    drivers/base/node,memory: rename function to match interface
    drivers/base/node: rename unregister_mem_blk_under_nodes() to be more
    acurate
    drivers/base/node: add unregister_mem_block_under_nodes()
    mm: memory,memlayout: add refresh_memory_blocks() for Dynamic NUMA.
    page_alloc: use dnuma to transplant newly freed pages in
    __free_pages_ok()
    page_alloc: use dnuma to transplant newly freed pages in
    free_hot_cold_page()
    page_alloc: transplant pages that are being flushed from the per-cpu
    lists
    x86: memlayout: add a arch specific inital memlayout setter.
    init/main: call memlayout_global_init() in start_kernel().
    dnuma: memlayout: add memory_add_physaddr_to_nid() for memory_hotplug
    x86/mm/numa: when dnuma is enabled, use memlayout to handle memory
    hotplug's physaddr_to_nid.
    mm/memory_hotplug: VM_BUG if nid is too large.
    mm/page_alloc: in page_outside_zone_boundaries(), avoid premature
    decisions.
    mm/page_alloc: make pr_err() in page_outside_zone_boundaries() more
    useful
    mm/page_alloc: use manage_pages instead of present pages when
    calculating default_zonelist_order()
    mm: add a early_param "extra_nr_node_ids" to increase nr_node_ids
    above the minimum by a percentage.

    Documentation/kernel-parameters.txt | 6 +
    arch/x86/mm/numa.c | 32 ++-
    drivers/base/memory.c | 55 ++++-
    drivers/base/node.c | 70 ++++--
    include/linux/dnuma.h | 97 ++++++++
    include/linux/memlayout.h | 134 +++++++++++
    include/linux/memory.h | 5 +
    include/linux/memory_hotplug.h | 4 +
    include/linux/mm.h | 7 +-
    include/linux/node.h | 20 +-
    include/linux/page-flags.h | 19 ++
    include/linux/rbtree.h | 12 +
    init/main.c | 2 +
    lib/rbtree.c | 40 ++++
    mm/Kconfig | 54 +++++
    mm/Makefile | 2 +
    mm/dnuma.c | 432 ++++++++++++++++++++++++++++++++++++
    mm/internal.h | 13 +-
    mm/memlayout-debugfs.c | 339 ++++++++++++++++++++++++++++
    mm/memlayout-debugfs.h | 39 ++++
    mm/memlayout.c | 354 +++++++++++++++++++++++++++++
    mm/memory_hotplug.c | 54 +++--
    mm/page_alloc.c | 154 +++++++++++--
    23 files changed, 1866 insertions(+), 78 deletions(-)
    create mode 100644 include/linux/dnuma.h
    create mode 100644 include/linux/memlayout.h
    create mode 100644 mm/dnuma.c
    create mode 100644 mm/memlayout-debugfs.c
    create mode 100644 mm/memlayout-debugfs.h
    create mode 100644 mm/memlayout.c

    --
    1.8.2.2



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