htcacheclean ignoring -l (limit)?

[Matthew Tice]

I'm running apache 2.2.9 on several nodes that serve static content only.
I'm running into a problem where the disk cache is filling up (and
subsequently problems serving the files).  I've the following configuration:

# /etc/fstab
tmpfs /www/cache tmpfs auto,rw,size=1200M,nr_inodes=1M 0 0

# ps aux | grep htcacheclean
/opt/apache2/bin/htcacheclean -d10 -t -p/www/cache -l750M

# httpd.conf
    LoadModule cache_module         modules/mod_cache.so
    LoadModule disk_cache_module    modules/mod_disk_cache.so
    LoadModule mem_cache_module     modules/mod_mem_cache.so

    ##################
    ## Cache Config ##
    ##################
    CacheRoot /www/cache
    # The default expire time for items in seconds:
    CacheDefaultExpire 14400
    CacheIgnoreCacheControl On
    CacheEnable disk /img
    CacheEnable disk /images
    CacheEnable disk /aimages
    CacheEnable disk /css
    CacheEnable disk /js
    ###################
    ## DCache config ##
    ###################
    # Maximum size of disk to use for caching in kbytes:
    CacheDirLength 6
    CacheDirLevels 3
    # Maximum size of object to disk cache in bytes:
    CacheMaxFileSize 100000

and the appropriate <Directory> directives.

So I've setup the disk_cache on a tmpfs and I'm running htcacheclean every
10 minutes to trim the cache down to 750M.  If I run a df -h on that
filesystem I see that I've passed that 750M mark:

Filesystem            Size  Used Avail Use% Mounted on
tmpfs                 1.2G  926M  275M  78% /www/cache

I'm not sure what I'm missing here.  The only thing I can think of is that
htcacheclean will only clean down to the limit if there is content that is
expired and needs to be removed (all the content is below the 4 hour expire
time).

Any insights would be appreciated.

Matt