Cache questions

[Jim Ohlstein]

I'm using the fastcgi cache for static files (images, javascript,css) 
and just found multiple lines in the error log like this one:

2009/07/10 10:22:54 [crit] 22476#0: ngx_slab_alloc() failed: no memory 
in cache keys zone "one"

So I increased the memory available for the zone and reloaded nginx. It 
took over five hours to go through the cache but these are the relevant 
entries:

2009/07/10 12:11:03 [notice] 21038#0: start cache manager process 32730
2009/07/10 12:11:04 [notice] 21038#0: cache manager process 22480 exited 
with code 0

and finally

2009/07/10 17:43:27 [notice] 32730#0: http file cache: 
/usr/local/nginx/cache 11638.289M, bsize: 4096

My questions are:

Is that simply the total (11638.289MB or 11.4GB) of all of the file 
sizes, or is that the actual disk space consumed taking into account 
total number of blocks used multiplied by the block size? The number 
could be quite different given what I estimate are nearly one million 
mostly small files in the cache at this point.

When I next upgrade nginx (I'm running 0.8.4), and I attempt a "graceful 
upgrade" will it have to go through this entire process again?