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    SubjectRe: [RFC 3/3] man-pages: Add man page for vmpressure_fd(2)
    On Tue, Nov 20, 2012 at 10:12:28AM -0800, David Rientjes wrote:
    > On Mon, 19 Nov 2012, Anton Vorontsov wrote:
    >
    > > We try to make userland freeing resources when the system becomes low on
    > > memory. Once we're short on memory, sometimes it's better to discard
    > > (free) data, rather than let the kernel to drain file caches or even start
    > > swapping.
    > >
    >
    > To add another usecase: its possible to modify our version of malloc (or
    > any malloc) so that memory that is free()'d can be released back to the
    > kernel only when necessary, i.e. when keeping the extra memory around
    > starts to have a detremental effect on the system, memcg, or cpuset. When
    > there is an abundance of memory available such that allocations need not
    > defragment or reclaim memory to be allocated, it can improve performance
    > to keep a memory arena from which to allocate from immediately without
    > calling the kernel.
    >

    A potential third use case is a variation of the first for batch systems. If
    it's running low priority tasks and a high priority task starts that
    results in memory pressure then the job scheduler may decide to move the
    low priority jobs elsewhere (or cancel them entirely).

    A similar use case is monitoring systems running high priority workloads
    that should never swap. It can be easily detected if the system starts
    swapping but a pressure notification might act as an early warning system
    that something is happening on the system that might cause the primary
    workload to start swapping.

    --
    Mel Gorman
    SUSE Labs


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