What happened to the vm.pagecache kernel tunable in RHEL 5?

Issue

It seems that at some point in the kernel's lifetime, the documentation in /usr/share/doc/kernel-*/Documenation/filesystems/proc.txt in section 2.4 dropped the bit about /proc/sys/vm/pagecache, which still exists.

In RHEL3, /proc/sys/vm/pagecache was a tunable with three parameters: min, borrow, and max.  But in RHEL5 it looks like it just has one value:

# cat /proc/sys/vm/pagecache 
100

and without documentation in the kernel-doc RPM, we have no idea what this value means.