Messages in this thread | | | Date | Fri, 29 Feb 2008 19:29:53 +0200 | From | Dimitrios Apostolou <> | Subject | Re: swap file over jffs2 partition |
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Jörn Engel wrote: > On Fri, 29 February 2008 04:50:17 +0200, Dimitrios Apostolou wrote: >> 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* >> swap...). And to avoid wearing out the flash storage too fast, I 'm >> thinking to format the 1GB partition as JFFS2, and create the swapfile >> on top of it. >> >> I'm not so experienced with JFFS and I don't know if it's too heavy for >> the CPU, for swapping. Or if there are other issues I 'll face. What do >> you think about it? Any other ways you 'd propose? >> >> Sorry for sending this at LKML but jffs-dev mailing list seems to be >> off. And JFFS is the only in-kernel filesystem that does wear-leveling, >> right? > > Replying in reverse order... > > The relevant mailing list is linux-mtd, added to Cc:. JFFS and JFFS2 > are two different things, JFFS is older and was removed from the kernel > not too long ago.
Thanks and sorry for intruding LKML. It seems that even wikipedia has wrong address for the mailing list, see the last link of the article:
http://en.wikipedia.org/wiki/JFFS2
> > The real fun comes not from CPU usage, but from interactions with the > memory management subsystem. In a nutshell, JFFS2 may require memory in > order to write data. When the system is under memory pressure, it needs > JFFS2 to write out pages, which will try to allocate memory. It is > theoretically possible to deadlock the system in this way.
Interesting. I guess nobody has experimented with it yet so I'll try. Unfortunately it seems I'll face another problem, that JFFS2 doesn't support having a swap-file at all. Why would this happen? More info:
http://dev.laptop.org/ticket/6469
> > On the plus side, the write path of JFFS2 is relatively simple and > extremely low-latency. It shouldn't be too hard to review the code and > handle all problem cases wrt. memory allocations. > > One issue that is hard to solve is space reservation. JFFS2 compresses > data and allows users to write as long as there is space remaining. It > is possible to swap out data that compresses well, have some other > process fill up the filesystem, then try to swap out data that > compresses badly and get -ENOSPC in return. As a system administrator > you can prevent others from ever writing to JFFS2 - and you better do!
Of course! I intend to use all the 1GB of flash only for swap, the system will be practically diskless. And I don't think enabling compression for such a task would be wise.
> > Jörn >
Thanks for the help, Dimitris -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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