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    SubjectRe: [RFC 1/3] /dev/low_mem_notify
    On Wed, 18 Jan 2012, Minchan Kim wrote:
    > I didn't look into your code(will do) but as I read description,
    > still I don't convince we need really some process specific threshold like 99%
    > I think application can know it by polling /proc/meminfo without this mechanism
    > if they really want.

    I'm not sure if we need arbitrary threshold either. However, we need to
    support the following cases:

    - We're about to swap

    - We're about to run out of memory

    - We're about to start OOM killing

    and I don't think your patch solves that. One possibility is to implement:

    VMNOTIFY_TYPE_ABOUT_TO_SWAP
    VMNOTIFY_TYPE_ABOUT_TO_OOM
    VMNOTIFY_TYPE_ABOUT_TO_OOM_KILL

    and maybe rip out support for arbitrary thresholds. Does that more
    reasonable?

    As for polling /proc/meminfo, I'd much rather deliver stats as part of
    vmnotify_read() because it's easier to extend the ABI rather than adding
    new fields to /proc/meminfo.

    On Wed, 18 Jan 2012, Minchan Kim wrote:
    > I would like to notify when system has a trobule with memory pressure without
    > some process specific threshold. Of course, applicatoin can't expect it.(ie,
    > application can know system memory pressure by /proc/meminfo but it can't know
    > when swapout really happens). Kernel low mem notify have to give such notification
    > to user space, I think.

    It should be simple to add support for VMNOTIFY_TYPE_MEM_PRESSURE that
    uses your hooks.

    Pekka


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