Memory Usage of BIRD

[Ondrej Zajicek]

On Thu, Dec 03, 2009 at 12:33:22PM +0100, Wolfgang Hennerbichler wrote:
> >> Hi Folks,
> >> 
> >> I just made a little experiment:
> >> * let BIRD peer with a router that has Full Feed
> >> * letting BIRD eat Full Feed (and tweet) - memory footprint ~ 130 MB BTW 
> >> (64 Bit Linux)
> >> * shutting the session down on the router-side
> >> * BIRD's memory consumption decreased to 128 MB, but was never freed  
> >> again.
> > 
> > This is probably caused by memory fragmentation and is otherwise harmless.
> > You can try that if you shut down the session and after a while shut up
> > the session, the memory footprint shouldn't be much larger than initially
> > (memory that was freed by BIRD but not released to OS is reused).
> 

> diggin up this old thread. I just did a test on that behaviour on
> Linux and FreeBSD. If sessions go down, the routing tables go empty, and
> even the protocols are disabled on Linux (64 Bit) BIRD doesn't free the
> memory to the OS. Or Linux doesn't reclaim the free memory. 
> ...
> On FreeBSD the behaviour is different, FreeBSD gets back most of
> BIRD's unused memory. Maybe we can look at this together. 

I would expect that this is not a bug in BIRD, but a behavior of glibc
memory management code (cause by memory fragmentation of heap and
reluctancy of glibc to return memory to the kernel). There are three
levels in memory management - program, libc and kernel. If program frees
some memory to libc and libc does not free it to kernel, it counts as a
memory consumption of that process (from the external point of view) and
kernel cannot reclaim that memory. This problem is general and
well-known and might be mitigated by some precautions, but i don' think
it is worth the work now.

-- 
Elen sila lumenn' omentielvo

Ondrej 'SanTiago' Zajicek (email: santiago at crfreenet.org)
OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net)
"To err is human -- to blame it on a computer is even more so."
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