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    SubjectRe: why swap at all?
    Quote from Roger Luethi <rl@hellgate.ch>:
    > On Wed, 26 May 2004 02:38:23 -0400, Anthony DiSante wrote:
    > > Now I buy another 256MB of ram, so I have 512MB of real memory. Why not
    > > just disable my swap completely now? I won't have increased my memory's
    > > size at all, but won't I have increased its performance lots?
    > >
    > > Or, to make it more appealing, say I initially had 512MB ram and now I have
    > > 1GB. Wouldn't I much rather not use swap at all anymore, in this case, on
    > > my desktop?
    >
    > Swap serves another (often underrated) purpose: Graceful degradation.
    >
    > If you have a reasonably amount of swap space mounted, you will know
    > you are running out of RAM because your system will become noticeably
    > slower. If you have no swap whatsoever, your first warning will quite
    > possibly be an application OOM killed or losing data due to a failed
    > memory allocation.
    >
    > Think of the slowness of swap as a _feature_.

    There is a very negative side to this approach as well, especially if users
    allocate excessive swap space.

    A run-away process on a server with too much swap can cause it to grind to
    almost a complete halt, and become almost compltely unresponsive to remote
    connections.

    If the total amount of storage is just enough for the tasks the server is
    expected to deal with, then a run-away process will likely be terminated
    quickly stopping it from causing the machine to grind to a halt.

    If, on the other hand, there is excessive storage, it can continue running
    for a long time, often consuming a lot of CPU.

    When the excess storage is physical RAM, this might not be particularly
    disasterous, but if it's swap space, it's much more likely to cause a serious
    drop in performance.

    For a desktop system, it might not be a big deal, but when it's an ISP's server
    in a remote data centre, it can create a lot of unnecessary work.

    John.
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