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    Subject[RFC][PATCH 0/7] memcg async reclaim
    Hi, thank you for all comments on previous patches for watermarks for memcg.

    This is a new series as 'async reclaim', no watermark.
    This version is a RFC again and I don't ask anyone to test this...but
    comments/review are appreciated.

    Major changes are
    - no configurable watermark
    - hierarchy support
    - more fix for static scan rate round robin scanning of memcg.

    (assume x86-64 in following.)

    'async reclaim' works when
    - usage > limit - 4MB.
    - usage < limit - 8MB.

    when the limit is larger than 128MB. This value of margin to limit
    has some purpose for helping to reduce page fault latency at using
    Transparent hugepage.

    Considering THP, we need to reclaim HPAGE_SIZE(2MB) of pages when we hit
    limit and consume HPAGE_SIZE(2MB) immediately. Then, the application need to
    scan 2MB per each page fault and get big latency. So, some margin > HPAGE_SIZE
    is required. I set it as 2*HPAGE_SIZE/4*HPAGE_SIZE, here. The kernel
    will do async reclaim and reduce usage to limit - 8MB in background.

    BTW, when an application gets a page, it tend to do some action to fill the
    gotton page. For example, reading data from file/network and fill buffer.
    This implies the application will have a wait or consumes cpu other than
    reclaiming memory. So, if the kernel can help memory freeing in background
    while application does another jobs, application latency can be reduced.
    Then, this kind of asyncronous reclaim of memory will be a help for reduce
    memory reclaim latency by memcg. But the total amount of cpu time consumed
    will not have any difference.

    This patch series implements
    - a logic for trigger async reclaim
    - help functions for async reclaim
    - core logic for async reclaim, considering memcg's hierarchy.
    - static scan rate memcg reclaim.
    - workqueue for async reclaim.

    Some concern is that I didn't implement a code for handle the case
    most of pages are mlocked or anon memory in swapless system. I need some
    detection logic to avoid hopless async reclaim.

    Any comments are welcome.


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