I have a memory/cpu monitor running, and sometimes see the graph line for “cached memory” drop, for no apparent reason.
Earlier today Cache memory was at about 4.8GB but then dropped in two steps ( a small and a big ), to 2.3GB.
I was not deleting files, sometimes it happens when I run Baobab (disk usage analyser, a graphical recursive version of du).
Kernel is: Linux 2.6.32-5-686-bigmem
2013-jan-29 It did it again this time the amount dropped was a lot smaller than what was already free, so I don't think it is dropping it so that [some of] the memory can be used for something else.
dark blue=buffers, red=application, green=cache, cyan=total