topic Re: Swapping ? Or Paging? in Operating System - HP-UX

Swapping ? Or Paging?

Alzhy — Wed, 05 May 2004 08:51:46 GMT

'Been reading here posts mentioning "systems should not swap, swap use should be 0".. but isn't it that modern Unices (and Linux) did away with swapping eons ago and replaced it with paging ?

With typical database processes in the range of 10's of Gigabytes of VM image.. I don't think swapping (offloading entire processes to disk) will still work but "paging" (offloading pages of memory to disk) does..

Just posting this question becuase I am often ask... are we swapping? And I always tell them.. UNIX systems these days no longer do swapping but paging..

Re: Swapping ? Or Paging?

Sanjay_6 — Wed, 05 May 2004 08:54:22 GMT

I think the two terms mean the same thing.

Swapping is paging and paging is swapping. we are still in ice age where we prefer to use swap when referring to paging under unix.

Hope this helps.

Regds

Re: Swapping ? Or Paging?

Stefan Farrelly — Wed, 05 May 2004 08:56:40 GMT

Youre technically right, it should be referred to as paging (when memory is being moved to disk and back). For us oldies though were still used to the word swapping to describe this.

Re: Swapping ? Or Paging?

Jeff Schussele — Wed, 05 May 2004 08:58:52 GMT

Hi Nelson,

Well I just want to point out that now HP calls it deactivation & reactivation.
What used to be called swapping a page out is now referred to as deactivating a page & when swapped in it's called reactivating a page.
Any way you put it - you don't want it happening on your system.

Rgds,
Jeff

Re: Swapping ? Or Paging?

Mark Grant — Wed, 05 May 2004 09:00:47 GMT

It is called "paging" and it is "paging". However, the number of people who know what you mean if you say "swapping" is far greater than if you say "paging".

Also, "swapping" suggests bad things are happening and therefore gets peoples attention more. We should, perhaps define "swapping" as "paging in and out because of memory pressure" instead of all the everyday paging in and out that goes on.

Re: Swapping ? Or Paging?

Pete Randall — Wed, 05 May 2004 09:04:01 GMT

Since the activity occurs in an area called the "swap area", I, for some strange reason, continue to call it swapping, though the activity is technically called paging.

Pete

Re: Swapping ? Or Paging?

A. Clay Stephenson — Wed, 05 May 2004 09:06:03 GMT

You are correct. It was a big deal back when the change was made from whole-process swapping to demand paging but for most flavors of UNIX that occurred sometime in the 1980's. Nowadays the two terms are used almost interchangably although they definitely mean different things. However, the anachronisms extend further: "swap space" rather than "paging space", the command (and system call) is "swapon" rather than pageon, "swapinfo" rather than "pageinfo" ...

In real life nowadays the point is almost moot because in the 1980's machines were expected to page (or swap) routinely and it was considered normal; now, when memory is so cheap and the performance penalty is so high, machines are usually configured to never page (or swap).

Re: Swapping ? Or Paging?

Alzhy — Wed, 05 May 2004 09:10:12 GMT

Whoa! Am not worthy....!

Jeez.. thanks a lot for the replies ye Caesars and Pharaos of this illustrious group.