why the swapping

David Gilbert dgilbert at dclg.ca
Thu May 18 09:56:49 PDT 2006

>>>>> "Tim" == Tim Middleton <x at vex.net> writes:

Tim> Running 6.0-release, with 2 gig ram. Typical memory stats like
Tim> this (from top):

Tim> 626M Active, 1045M Inact, 204M Wired, 75M Cache, 112M Buf, 22M
Tim> Free

Tim> Under moderately high load i'm seeing a lot of swapping
Tim> periodically through the day (and then load avg going way, way
Tim> up, of course). I'm wondering why is there, with so much inactive
Tim> memory, so much disk swapping?

Tim> The machine runs some fairly intense stuff, such as squid,
Tim> postgresql, and zope; but it seems to me there should be enough
Tim> RAM to cover all of this without swapping. What am I missing? Am
Tim> i misinterpretting the stats, and just not understanding how the
Tim> vm works?

Swapping in or out?  Sswapping out is normal behaviour --- a
background kernel thread sweeps memory to move it from active to
inactive and inactive dirty pages are occaisionally sent to swap (or
the file that's backing them).

Swapping in is also normal when processes are launched.  Remember that
*BSD's "swap in" processes.

I believe that mmap() calls also show up in the swap stats ...

Swapping doesn't mean what it used to.  What should worry you is a
process that is blocked to a large degree on paging --- but that's not
likely happening.


|David Gilbert, Independent Contractor.       | Two things can be          |
|Mail:       dave at daveg.ca                    |  equal if and only if they |
|http://daveg.ca                              |   are precisely opposite.  |

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