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    SubjectRe: [PATCH 0/3] OOM detection rework v4
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    On 03/03/2016 03:10 PM, Joonsoo Kim wrote:
    >
    >> [...]
    >>>>> At least, reset no_progress_loops when did_some_progress. High
    >>>>> order allocation up to PAGE_ALLOC_COSTLY_ORDER is as important
    >>>>> as order 0. And, reclaim something would increase probability of
    >>>>> compaction success.
    >>>>
    >>>> This is something I still do not understand. Why would reclaiming
    >>>> random order-0 pages help compaction? Could you clarify this please?
    >>>
    >>> I just can tell simple version. Please check the link from me on another reply.
    >>> Compaction could scan more range of memory if we have more freepage.
    >>> This is due to algorithm limitation. Anyway, so, reclaiming random
    >>> order-0 pages helps compaction.
    >>
    >> I will have a look at that code but this just doesn't make any sense.
    >> The compaction should be reshuffling pages, this shouldn't be a function
    >> of free memory.
    >
    > Please refer the link I mentioned before. There is a reason why more free
    > memory would help compaction success. Compaction doesn't work
    > like as random reshuffling. It has an algorithm to reduce system overall
    > fragmentation so there is limitation.

    I proposed another way to get better results from direct compaction -
    don't scan for free pages but get them directly from freelists:

    https://lkml.org/lkml/2015/12/3/60

    But your redesign would be useful too for kcompactd/khugepaged keeping
    overall fragmentation low.

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