mem_node memory usage in 2.x

(This also may be an issue in Squid-3, as the mem_node class stores the data
inline.)

I did a little poking with the FreeBSD allocator - it allocates non-tiny
objects on page boundaries with a size rounded up to the next page.

[adrian@sarah ~]$ ./test1 test1 131072
allocating 12, then 4096 byte structures 131072 times..
RSS: 536868
[adrian@sarah ~]$ ./test1 test2 131072
allocating 4108 byte structure 131072 times..
RSS: 1059244

The source is available here:

http://www.creative.net.au/diffs/mem-size.c

I believe newer allocators do this sort of thing. Could people on other platforms
(Linux, Solaris, Windows? :) give the above a whirl and let me know what the
output is?

I'm going to revisit my (much) earlier work which folded the 4k buffer into the
mem_node and look at unwinding it. Its easy to do everywhere -except- the write
path and thats all very dirty.

That -should- drop the memory usage for large memory caches a bit.
It'll increase the allocator usage a bit but then there are other
much larger abuses of the allocator out there.

Comments?

Adrian

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