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SubjectRe: Memory Mapped Filesystem
Hi!
>
> I converted yesterday an Alpha station to ext3 (and it works great).
> However, I kept /tmp as ext2 since the README distributed with ext3 says
> that it would be more efficient this way. This is somehow inelegant,
> since this means that there is still one fsck (which can fail).
>
> I could do an automatic mke2fs on the device, at boot time, since this
> is /tmp. However, with automatic numbering of partitions, I feel a bit
> unsafe with a mke2fs in a boot script.
>
> So I remembered that, under FreeBSD, I use mfs for /tmp: a filesystem
> mapped in memory. This is not quite a ramdisk since:
> -- it can be swapped out
> -- it frees unsued pages when a file is removed
> Somehow, this is like sharing space for /tmp and swap. I find this
> scheme elegant and it would fit my needs.
>
> Therefore, I intend to implement such a filesystem. For this, I need
> some help; specifically, I ask myself the following questions:
> -- does such a filesystem already exists ?

I think so.

> -- would it be easier to modify the ramdisk to be able to be
> swapped out, and stubs in one filesystem to unmap unused pages ?
> -- how do I allocate memory from within the kernel, such that this
> memory might be swapped out ? I can do a do_mmap(), but, from
> my (rather low) understanding of the memory management in Linux,
> this mapping would be specific to one process. I could run
> a kernel thread (well, at least I believe I could) but I would
> run into the "Minix-single-threaded-filesystem".
> -- what happens if I create a file on such a filesystem and try to
> swapon it ?
> -- does all this make sense ? Is there a better solution ?

Are you sure /tmp is used so much it makes sense?
Pavel
--
I'm pavel@ucw.cz. "In my country we have almost anarchy and I don't care."
Panos Katsaloulis describing me w.r.t. patents me at discuss@linmodems.org

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