On Sunday 13 November 2011 08:32, John J. Boyer wrote:
Why does Linux do this? It seems odd to me.
Suppose you have 4 Gb of RAM, of which only 1 Gb is used. What good is the other 3 Gb doing you? You might as well not have it at all.
Instead of leaving the RAM unused, Linux uses it as a cache. It can't hurt, and it can help. If a programme needs the memory, Linux will make it available to the programme quickly enough.
"free" gives me the following report:
$ free total used free shared buffers cached Mem: 4147456 3991600 155856 0 98556 2739992 -/+ buffers/cache: 1153052 2994404 Swap: 3911788 248 3911540
Therefore, I have 4 Gb of RAM, of which about 1 Gb is used for the programmes and a little under 3 Gb is used as a cache.
Apparently Windows finally decided to use a similar approach, which it calls SuperFetch.
I'm not sure how to disable the cache entirely, but to clear it, with kernel 2.6.16 or later, do the following as root:
sync ; echo 3 > /proc/sys/vm/drop_caches