Compressed RAM disk swap space

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Compressed RAM disk swap space

David-3
Hi, I have tried something which actually boosts performance: a
compressed RAM disk used as swap space.  As an end user, I do a lot of
testing on PC-BSD and Ubuntu.  It was suggested in the PC-BSD forums I
put my idea in one of these mailing lists.

The compressed RAM disk I tested is called "zRam" and I use it on
Ubuntu.  It makes a noticeable difference on older computers e.g. 1GB of
RAM.  Would the same feature work in FreeBSD and PC-BSD?  I use PC-BSD.  
The zRam feature really *does* boost performance.  As an end-user, I
don't know exactly how it works; I just installed it from the "Software
Centre" in Ubuntu and enjoy the performance boost and I have noticed the
hard disk is not constantly in use, compared to not using zRam.

You can see my original posting in the PC-BSD forums:

http://forums.pcbsd.org/showthread.php?t=18557

Hope this idea is considered. :)





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Re: Compressed RAM disk swap space

Achim Patzner
Am 09.11.2012 um 13:33 schrieb David <[hidden email]>:
> Hi, I have tried something which actually boosts performance

It doesn't; it just moves the load from one limited resource (RAM) to another one (CPU cycles), adding its own overhead on the way. It just means that your machine got too large an engine for your tires. Save on CPU power and get more RAM next time.

> : a compressed RAM disk used as swap space.

It nearly sounds as good as "hey, we've got virtual memory, let's generate an incredibly large RAM disk". To me it sounds like investing into sovereign debt of your home country and paying your interest rate with your own increased taxes. Why swap into RAM if your process could use it as well?

About the cost of compression: This idea was already annoying decades ago (doesn't anyone remember those "RAM extenders" for MS-DOS that gave you "more RAM than your computer contains"?) when software suddenly got inexplicably slow (until you found the driver chewing on its own tail by trying to decompress itself) and was one of the reasons I moved to SCO and BSD/386.


Achim

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