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    SubjectRe: [resent PATCH] Re: very slow parallel read performance
    Date
    On August 25, 2001 06:28 pm, pcg@goof.com ( Marc) (A.) (Lehmann ) wrote:
    > On Sat, Aug 25, 2001 at 12:50:51PM -0300, Rik van Riel
    <riel@conectiva.com.br> wrote:
    > > Remember NL.linux.org a few weeks back, where a difference of
    > > 10 FTP users more or less was the difference between a system
    > > load of 3 and a system load of 250 ? ;)
    >
    > OTOH, servers the use a single process or thread per connection are
    > destined to fail under load ;)

    There's an obvious explanation for the high loadavg people are seeing when
    their systems go into thrash mode: when free is exhausted, every task that
    fails to get a block in __alloc_pages will become PF_MEMALLOC and start
    scanning. The remaining tasks that are still running will soon also fail in
    __alloc_pages and jump onto the dogpile. This is a pretty clear
    demonstration of why the current "self-help" strategy is flawed.

    Those tasks that can't get memory should block, leaving one or two threads to
    sort things out under predictable conditions, then restart the blocked
    threads as appropriate.

    --
    Daniel
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