very strange reaction of the md disks
olli at lurza.secnetix.de
Wed Jun 11 16:36:27 UTC 2008
I don't know why nobody else has given the correct answer
to this (it's should actually be a FAQ). So I'll try to
give an answer.
The Ghost <the-ghost at inbox.ru> wrote:
> Maybe I just don't understand something, but anyway, it looks really odd.
> I have a machine with 2 Gb RAM with a clean newly-installed
> FREEBSD-7.0-RELEASE. I make two 300-MB mdconfig disks and populate
> them, and when the first one was already full and the second one is
> only half-full, I get a kernel panic "not enough memory".
Use "-t swap" with mdconfig(8), not "-t malloc".
> I was very surprised to see that one gigabyte of my
> memory suddenly became used up.
FreeBSD uses all memory for caching, as far as possible.
Free memory is wasted memory.
> A friend of mine told me that such a panic is really a thing to write
> a bugreport on it,
No. It is clearly documented in the mdconfig(8) manpage:
"If the -o reserve option is not set, creating and filling
a large malloc-backed memory disk is a very easy way to
panic a system."
As I said above, you probably don't want a malloc-backed
memory disk (which means it consumes non-pagable kernel
memory), but a swap-backed disk (which is cached in regular
RAM and backed by swap).
If you're absolutely sure you want kernel-malloc for your
memory disk, you need to increase the kmem limit (see
"sysctl vm | grep kmem").
Oliver Fromme, secnetix GmbH & Co. KG, Marktplatz 29, 85567 Grafing b. M.
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