Mailinglist Archive: opensuse (3666 mails)

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Re: [SLE] Maximum swap size
  • From: Anders Johansson <andjoh@xxxxxxxxxx>
  • Date: Sun, 6 Mar 2005 23:18:14 +0000
  • Message-id: <200503062318.15150.andjoh@xxxxxxxxxx>
On Sunday 06 March 2005 23:10, Hans Witvliet wrote:
> I allready though so,
> For most "normal" situations, sysadmins consider swap nowadays more as a
> protection meganism against kernel panics.
>
> Used to be different. I recall the days (on a dec vax/vms 780) and
> several hundred people working on it, and on piek moments during the
> week, most of us were watching which users were swapped out ;-))
> At that time "swapped/paged-out" was a fact of life. But since then,
> CPU, cache and mem-speed have rissen 1000-fold; while "background"
> -memory, or disks in general perhaps 10 or 20-fold.
> So the effect of a process being swapped out of main-memory is felt much
> more.
>
> At the HP-UX training classes we were told if a system was using swap
> intens and for a longer period, one should prepare for several things:
> -Complaining users (bad system response)
> -Looking for bad code
> -Start procedures for buying additional memory
>
> So over-commiting your memory (thus swapping) is something to avoid at
> all costs.
>
> Only perfect sense for swapping a processes on purpose, might be in a
> cluster environment, to re-distribute cpu-load....

Swapping has other uses. Swapping rarely used data from main internal memory
to free up space for disk cache and read-ahead buffers can improve
performance. This is why you can sometimes see swap usage even though you
have a gigabyte free.

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