Memory leak on 5.1-RELEASE?

[dpk]

(I'm not a member of the list; please Cc me on any replies.)

We're running Apache 1.3.28 on a 5.1-RELEASE machine. It's a Dell PE 2650
w/ 2GB RAM. The site contains a lot of large files (multi-megabyte) -
otherwise there's nothing unusual running.

The Active memory use, according to top, seems rather high:

last pid: 21487;  load averages:  0.19,  0.33,  0.32    up 2+16:45:20  15:52:21
76 processes:  1 running, 75 sleeping
CPU states:  0.5% user,  0.0% nice,  4.0% system,  1.4% interrupt, 94.2% idle
Mem: 1413M Active, 187M Inact, 299M Wired, 93M Cache, 112M Buf, 2632K Free
Swap: 1024M Total, 21M Used, 1003M Free, 2% Inuse

We can't seem to get the Active number down much, even after stopping
Apache it still stays around 1100M. There's no shared memory in use, and
nothing in vmstat -m seems to indicate where the "missing" memory is. top,
sorting by "size", does not indicate anything unusual either.

sysctl vm.vmtotal says:

vm.vmtotal:
System wide totals computed every five seconds: (values in kilobytes)
===============================================
Processes:              (RUNQ: 1 Disk Wait: 0 Page Wait: 0 Sleep: 76)
Virtual Memory:         (Total: 8172K, Active 636472K)
Real Memory:            (Total: 2051312K Active 389176K)
Shared Virtual Memory:  (Total: 16436K Active: 11760K)
Shared Real Memory:     (Total: 6004K Active: 4436K)
Free Memory Pages:      79228K

whereas on other servers, the Real Memory "Active" number seems to match
the one found in top, on this one it is about 1GB lower.

A similar machine running Apache on 5.1-R, generally serving smaller
files, has the same problem in a smaller scale (about 640M even when
Apache is stopped).

Are there any other data that I should send to help diagnose this problem,
or any programs I can run to try and track this stray memory use down?

- dpk