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    SubjectRe: OOM kills if swappiness set to 0, swap storms otherwise


    Charles Shannon Hendrix wrote:
    > Mon, 27 Mar 2006 @ 19:59 -0800, Andrew Morton said:
    >
    >
    >> Much porkiness.
    >>
    >> /proc/meminfo is very useful for obtaining a top-level view of where all
    >> the memory's gone to. I'd tentatively say that your options are to put up
    >> with the swapping or find a new mail client.
    >>
    >
    > I use mutt for my email, and I have the same issue on a 1GB system.
    >
    > I really wish we could put an upper limit on what file cache can use.
    >
    ----
    Hmmm, not to be contrary, but I have a 1GB system that refuses to swap
    during large file i/o operations. For the first time in a *long* time,
    I read someone's suggestion to increase swappiness -- I did, to 75 or 80,
    (I've booted since then, so it's back to 60 and no swap usage) and some of
    the programs that rarely run actually swapped. It was great! I finally had
    more memory for file i/o operations.

    Maybe you are telling the system to "feel free" to use swap by having a
    large swap file? I have a 256Mb swap partition near the front of the disk
    where I/O is fastest, but it usually remains untouched, but that also means
    I can only overcommit used memory by 25% (1Gphys, 256M swap). I don't know
    what the OOM "looks like" when it runs. I had a buggy perlapp, once, that
    tried to consume infinite memory, but I think it segfaulted before the OOM
    could act.

    Maybe if you don't want linux to swap as much, it might swap less if
    you give
    it less to swap with? I know it sounds simplistic, but I've run with
    smallish
    swap files ever since I got up to 1GB of main memory. The only reason I
    have one
    at all is I presumed that infrequently used functions, like dhcp (only
    used when
    friends are over) would be shuffled out -- but it isn't unless I increase
    swappiness.
    > I shouldn't be suffering from swap storms.
    >
    I agree. Try getting rid of your swap file entirely -- your system will
    still
    run unless you are overloading memory, but you have a Gig. How much do you
    need to keep in memory? Sure, if/when I get a 4-way CPU (I have a 2-cpu
    setup now),
    I might go up to 4G, but I might be running multiple virtual machines too!
    > For example, my normal working set of programs eats about 250MB of memory. If
    > I also start a job running to something like tag some mp3s, copy a CD, or just
    > process a lot of files, it only takes a few minutes before performance becomes
    > unacceptable.
    >
    ---
    You might try the "cfq" block i/o algorithm. Then you can
    ionice down the disk priority of background processes (though you need
    to be root to reduce ionice levels at this point, unlike cpu nice).
    > If you are doing some work where you switch among several applications
    > frequently, the pigginess of file cache becomes a serious problem.
    >
    ---
    Never a problem. I don't allocate enough swap for it to be a
    problem I'm
    guessing. Programs stay in memory and blocks get forced out to disk more
    frequently.

    Linda
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