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    SubjectRe: Detecting page cache trashing state
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    Dne 15.9.2017 v 02:16 Taras Kondratiuk napsal(a):
    > Hi
    >
    > In our devices under low memory conditions we often get into a trashing
    > state when system spends most of the time re-reading pages of .text
    > sections from a file system (squashfs in our case). Working set doesn't
    > fit into available page cache, so it is expected. The issue is that
    > OOM killer doesn't get triggered because there is still memory for
    > reclaiming. System may stuck in this state for a quite some time and
    > usually dies because of watchdogs.
    >
    > We are trying to detect such trashing state early to take some
    > preventive actions. It should be a pretty common issue, but for now we
    > haven't find any existing VM/IO statistics that can reliably detect such
    > state.
    >
    > Most of metrics provide absolute values: number/rate of page faults,
    > rate of IO operations, number of stolen pages, etc. For a specific
    > device configuration we can determine threshold values for those
    > parameters that will detect trashing state, but it is not feasible for
    > hundreds of device configurations.
    >
    > We are looking for some relative metric like "percent of CPU time spent
    > handling major page faults". With such relative metric we could use a
    > common threshold across all devices. For now we have added such metric
    > to /proc/stat in our kernel, but we would like to find some mechanism
    > available in upstream kernel.
    >
    > Has somebody faced similar issue? How are you solving it?
    >
    Hi

    Well I witness this when running Firefox & Thunderbird on my desktop for a
    while on just 4G RAM machine till these 2app eat all free RAM...

    It gets to the position (when I open new tab) that mouse hardly moves -
    kswapd eats CPU (I've no swap in fact - so likely just page-caching).

    The only 'quick' solution for me as desktop user is to manually invoke OOM
    with SYSRQ+F key - and I'm also wondering why the system is not reacting
    better. In most cases it kills one of those 2 - but sometime it kills whole
    Xsession...


    Regards

    Zdenek

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