• Michal Hocko's avatar
    mm, memory_hotplug: do not associate hotadded memory to zones until online · f1dd2cd1
    Michal Hocko authored
    The current memory hotplug implementation relies on having all the
    struct pages associate with a zone/node during the physical hotplug
    phase (arch_add_memory->__add_pages->__add_section->__add_zone).  In the
    vast majority of cases this means that they are added to ZONE_NORMAL.
    This has been so since 9d99aaa3 ("[PATCH] x86_64: Support memory
    hotadd without sparsemem") and it wasn't a big deal back then because
    movable onlining didn't exist yet.
    
    Much later memory hotplug wanted to (ab)use ZONE_MOVABLE for movable
    onlining 511c2aba ("mm, memory-hotplug: dynamic configure movable
    memory and portion memory") and then things got more complicated.
    Rather than reconsidering the zone association which was no longer
    needed (because the memory hotplug already depended on SPARSEMEM) a
    convoluted semantic of zone shifting has been developed.  Only the
    currently last memblock or the one adjacent to the zone_movable can be
    onlined movable.  This essentially means that the online type changes as
    the new memblocks are added.
    
    Let's simulate memory hot online manually
      $ echo 0x100000000 > /sys/devices/system/memory/probe
      $ grep . /sys/devices/system/memory/memory32/valid_zones
      Normal Movable
    
      $ echo $((0x100000000+(128<<20))) > /sys/devices/system/memory/probe
      $ grep . /sys/devices/system/memory/memory3?/valid_zones
      /sys/devices/system/memory/memory32/valid_zones:Normal
      /sys/devices/system/memory/memory33/valid_zones:Normal Movable
    
      $ echo $((0x100000000+2*(128<<20))) > /sys/devices/system/memory/probe
      $ grep . /sys/devices/system/memory/memory3?/valid_zones
      /sys/devices/system/memory/memory32/valid_zones:Normal
      /sys/devices/system/memory/memory33/valid_zones:Normal
      /sys/devices/system/memory/memory34/valid_zones:Normal Movable
    
      $ echo online_movable > /sys/devices/system/memory/memory34/state
      $ grep . /sys/devices/system/memory/memory3?/valid_zones
      /sys/devices/system/memory/memory32/valid_zones:Normal
      /sys/devices/system/memory/memory33/valid_zones:Normal Movable
      /sys/devices/system/memory/memory34/valid_zones:Movable Normal
    
    This is an awkward semantic because an udev event is sent as soon as the
    block is onlined and an udev handler might want to online it based on
    some policy (e.g.  association with a node) but it will inherently race
    with new blocks showing up.
    
    This patch changes the physical online phase to not associate pages with
    any zone at all.  All the pages are just marked reserved and wait for
    the onlining phase to be associated with the zone as per the online
    request.  There are only two requirements
    
    	- existing ZONE_NORMAL and ZONE_MOVABLE cannot overlap
    
    	- ZONE_NORMAL precedes ZONE_MOVABLE in physical addresses
    
    the latter one is not an inherent requirement and can be changed in the
    future.  It preserves the current behavior and made the code slightly
    simpler.  This is subject to change in future.
    
    This means that the same physical online steps as above will lead to the
    following state: Normal Movable
    
      /sys/devices/system/memory/memory32/valid_zones:Normal Movable
      /sys/devices/system/memory/memory33/valid_zones:Normal Movable
    
      /sys/devices/system/memory/memory32/valid_zones:Normal Movable
      /sys/devices/system/memory/memory33/valid_zones:Normal Movable
      /sys/devices/system/memory/memory34/valid_zones:Normal Movable
    
      /sys/devices/system/memory/memory32/valid_zones:Normal Movable
      /sys/devices/system/memory/memory33/valid_zones:Normal Movable
      /sys/devices/system/memory/memory34/valid_zones:Movable
    
    Implementation:
    The current move_pfn_range is reimplemented to check the above
    requirements (allow_online_pfn_range) and then updates the respective
    zone (move_pfn_range_to_zone), the pgdat and links all the pages in the
    pfn range with the zone/node.  __add_pages is updated to not require the
    zone and only initializes sections in the range.  This allowed to
    simplify the arch_add_memory code (s390 could get rid of quite some of
    code).
    
    devm_memremap_pages is the only user of arch_add_memory which relies on
    the zone association because it only hooks into the memory hotplug only
    half way.  It uses it to associate the new memory with ZONE_DEVICE but
    doesn't allow it to be {on,off}lined via sysfs.  This means that this
    particular code path has to call move_pfn_range_to_zone explicitly.
    
    The original zone shifting code is kept in place and will be removed in
    the follow up patch for an easier review.
    
    Please note that this patch also changes the original behavior when
    offlining a memory block adjacent to another zone (Normal vs.  Movable)
    used to allow to change its movable type.  This will be handled later.
    
    [richard.weiyang@gmail.com: simplify zone_intersects()]
      Link: http://lkml.kernel.org/r/20170616092335.5177-1-richard.weiyang@gmail.com
    [richard.weiyang@gmail.com: remove duplicate call for set_page_links]
      Link: http://lkml.kernel.org/r/20170616092335.5177-2-richard.weiyang@gmail.com
    [akpm@linux-foundation.org: remove unused local `i']
    Link: http://lkml.kernel.org/r/20170515085827.16474-12-mhocko@kernel.orgSigned-off-by: default avatarMichal Hocko <mhocko@suse.com>
    Signed-off-by: default avatarWei Yang <richard.weiyang@gmail.com>
    Tested-by: default avatarDan Williams <dan.j.williams@intel.com>
    Tested-by: default avatarReza Arbab <arbab@linux.vnet.ibm.com>
    Acked-by: Heiko Carstens <heiko.carstens@de.ibm.com> # For s390 bits
    Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
    Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
    Cc: Andi Kleen <ak@linux.intel.com>
    Cc: Andrea Arcangeli <aarcange@redhat.com>
    Cc: Balbir Singh <bsingharora@gmail.com>
    Cc: Daniel Kiper <daniel.kiper@oracle.com>
    Cc: David Rientjes <rientjes@google.com>
    Cc: Igor Mammedov <imammedo@redhat.com>
    Cc: Jerome Glisse <jglisse@redhat.com>
    Cc: Joonsoo Kim <js1304@gmail.com>
    Cc: Mel Gorman <mgorman@suse.de>
    Cc: Tobias Regnery <tobias.regnery@gmail.com>
    Cc: Toshi Kani <toshi.kani@hpe.com>
    Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
    Cc: Xishi Qiu <qiuxishi@huawei.com>
    Cc: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    f1dd2cd1
memory_hotplug.h 9.34 KB