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    Subject[RFC] memory hotremove patch take 2 [00/10]


    I rebased and debugged Kame-san's memory hot-remove patches.
    This work is not finished yet. (Some pages keep un-removable status)
    But, I would like to show current progress of it, because it has
    been a long time since previous post, and some bugs are fixed.

    If you have concern, please check this. Any comments are welcome.



    These patches are for memory hot-remove.

    How to use
    - kernelcore=xx[GMK] must be specified at boottime option to create
    ZONE_MOVABLE area.
    - After bootup, execute following.
    # echo "offline" > /sys/devices/system/memory/memoryX/status

    Change log from previous version.
    - Rebase to 2.6.21-mm1.
    - Old original ZONE_MOVABLE code is removed. Mel-san's ZONE_REMOVABLE
    for anti-fragmentation is used.
    - Fix wrong return code check of isolate_lru_page()
    - Page is isolated ASAP, which was source of page migration when
    memory-hotremove. In old code, it uses just put_page(),
    and we expected that migrated source page is catched in
    __free_one_page() as isolated page. But, it is spooled in
    per_cpu_page and used soon for next destination page of migration.
    This was cause of eternal loop in offline_pages().
    - There is a page which is not mapped but added to swapcache in
    swap-in code. It was cause of panic in try_to_unmap(). fixed it.
    - end_pfn is rounded up at memmap_init. If there is a small hole on
    end of section. These page is not initialized.

    - There are some pages which are un-removable page on memory stress
    condition. (These pages are set PG_swapcache or PG_mappedtodisk
    without connecting to lru.)
    - Should make i386/x86-64/powerpc interface code. But not yet
    (really sorry :-( ).
    - If bootmem parameter or efi's memory map is stored by efi, memory
    can't be removed even if it is in removable zone.
    - node hotplug support. (this may needs some amount of patches.)
    - test under heavy work load and more careful race check.
    - Fix where we should allocate migration target page from.
    - Hmmmm.... And so on.

    [1] counters patch -- per-zone counter for ZONE_MOVABLE

    ==page isolation==
    [2] page isolation patch ..... basic defintions of page isolation.
    [3] drain_all_zone_pages patch ..... drain all cpus' pcp pages.
    [4] isolate freed page patch ..... isolate pages in free_area[]

    ==memory unplug==
    offline a section of pages. isolate specified section and migrate
    content of used pages to out of section. (Because free pages in a
    section is isolated, it never be returned by alloc_pages())
    This patch doesn't care where we should allocate migration new pages from.
    [5] memory unplug core patch --- maybe need more work.
    [6] interface patch --- "offline" interface support

    ==migration nocontext==
    Fix race condition of page migration without process context
    (not taking mm->sem). This patch delayes kmem_cache_free() of
    anon_vma until migration ends.
    [7] migration nocontext patch --- support page migration without
    acquiring mm->sem. need careful debug...

    ==other fixes==
    [8] round up end_pfn at memmap_init
    [9] page isolation ASAP when memory-hotremove case.
    [10] fix swapping-in page panic.

    Yasunori Goto

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