This patch implements a page cache that is invalidated in a LRU fashion.
Pages are added to the cache as soon as they become visible. When the cache is
full and a new page that isn't in the cache becomes visible, the least recently
viewed page in the cache is evicted from memory and the new one takes it's
place.
The cache size is configurable using the page-cache-size configuration
variable, with a default value of 15 pages. Very large values for the cache
size are not recommended, though, as it will stress the system memory out.
The old periodic page reclaiming code is no longer necessary with this patch,
so I removed it.
Special thanks to Ignas Anikevičius, and Sebastian Ramacher for the
inspirations.
Signed-off-by: Sebastian Ramacher <sebastian+dev@ramacher.at>
