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    SubjectRe: [RFC] Disk shock protection (revisited)
    On Thu, Feb 28, 2008 at 6:13 AM, Alan Cox <alan@lxorguk.ukuu.org.uk> wrote:
    > > > That sounds like a non starter. What if the box is busy, what if the
    > > > daemon or something you touch needs memory and causes paging ?
    > >
    > > The daemon runs mlock'd anyway, so there won't be any need for paging
    >
    > mlock does not guarantee anything of that form. A syscall by an mlocked
    > process which causes a memory allocation can cause paging of another
    > process on the system.
    >
    >
    > > there. As for responsiveness under heavy load, I'm not quite sure I get
    > > your meaning. On my system, at least, the only way I have managed to
    > > decrease responsiveness noticeably is to cause a lot of I/O operations
    >
    > It depends a lot on hardware but you can certainly get user space delays
    > in seconds as an extreme worst case.

    I don't know the details, but I believe the Linux-HA heartbeat daemons
    take significant effort to eliminate unexpected delays. See
    http://www.linux-ha.org/

    Lars Marowsky-Bree of Novell is extremely involved in the project and
    he at least occasionally posts on LKML. I've cc'ed him.

    Greg
    --
    Greg Freemyer
    Litigation Triage Solutions Specialist
    http://www.linkedin.com/in/gregfreemyer
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