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SubjectRe: why swap at all?
Hello!

> But swap behaviour kills performance even when memory is more than adequate.
> Consider building a DVD image in a 4GB system. The i/o forces all of the
> unused programs out, in spite of the fact that an extra 100MB doesn't make a
> measurable difference in performance. But when I click Mozilla paging most of
> it in from disk make a big difference in performance to the user.

I think that kernel cannot know that you need some data once or more.
This is fadvise for.
With my wrapper (http://kernel.umbrella.ro) for fadvise you can do this:
NOCA_SIZE=128 NOCA_READ=1 NOCA_WRITE=1 NOCA_RA=1 \
noca mkisofs -R -o /tmp/1.iso /tmp/data

This means:
NOCA_SIZE: Call fadvise only after 128KiB was read/wrote.
NOCA_RA: call fadvise with POSIX_FADV_SEQUENTIAL
NOCA_READ: use fadvise(POSIX_FADV_DONTNEED) for reads (because you don't
need anymore the source files)
NOCA_WRITE: use fadvise(POSIX_FADV_DONTNEED) for writes (because it's
useless to cache the end of the ISO)

Do this program resolve your problem?

> The problems with small memory are different in kind, when not even the
> programs will fit in memory at the same time, or will leave next to nothing
> for i/o, swap is required for performance. But on a large memory system I
> believe the gain to pain ratio is way too low with the current VM. The
> solution at the moment is to turn off swap, which as you note has other
> problems (can't move between zones without swap?) which in theory could
> really hang a system.
>
> --
> -bill davidsen (davidsen@tmr.com)
> "The secret to procrastination is to put things off until the
> last possible moment - but no longer" -me
> -
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>

---
Catalin(ux aka Dino) BOIE
catab at deuroconsult.ro
http://kernel.umbrella.ro/
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