Messages in this thread | | | Date | Fri, 29 Feb 2008 20:13:20 +0200 | From | Dimitrios Apostolou <> | Subject | Re: swap file over jffs2 partition |
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Bernd Petrovitsch wrote: > On Fre, 2008-02-29 at 04:50 +0200, Dimitrios Apostolou wrote: >> Hello list, >> >> I intend to build a diskless linux system (root over NFS). Because it >> has 1GB of embedded flash storage, I'm thinking of using this as swap >> (I've been bitten many times by the problems linux has with *no* > > Put more RAM on the hardware and/or reduce the software on it. > If that means heavily customizing the distribution: Do it. > If that means you can't run some specific common distribution[0]: Throw > it out and roll your own minimalistic one with just the tools and > especially libraries you need. > We run Linux on embedded hardware all the time without swapspace without > any problems (related to the "missing" swapspace).
I have been running swapless linux systems a long time ago, but I think I have had more problems than not. I have tried setting swappiness and overcommit settings but these don't help much. Let me explain:
When it is not certain that your system will run a specific task and only that, it is almost certain that sometime you will run out of memory. For example in the thin client case a user might open too many windows and fill the RAM with X server pixmaps...
So when the out of memory condition happens the system will start swapping. And if you have no swap enabled, the system will swap even harder: it will swap out all mmap'ed read-only memory segments, which mostly are the executables themselves. And because these will be needed immediately they will be swapped in immediately afterwards...
This renders the system *unusable* for all cases. Sometimes it even stops responding to ping... On the other hand if you have a swap partition then the kernel will choose to swap out other memory segments, not the executable ones that are so much needed.
> >> swap...). And to avoid wearing out the flash storage too fast, I 'm > > Swapping (and constantly writing logfiles) will wear it out much faster > than without. Perhaps not at development time but for sure in the field.
That's why I want to do it over a wear-levelling layer. Given that the partition is large enough it will hopefully take a while to wear it out.
Thanks, Dimitris
> > [....] > > Bernd > > [0]: Which I highly doubt.
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