vmscan: split LRU lists into anon & file sets

vmscan: split LRU lists into anon & file sets

Split the LRU lists in two, one set for pages that are backed by real file
systems ("file") and one for pages that are backed by memory and swap
("anon").  The latter includes tmpfs.

The advantage of doing this is that the VM will not have to scan over lots
of anonymous pages (which we generally do not want to swap out), just to
find the page cache pages that it should evict.

This patch has the infrastructure and a basic policy to balance how much
we scan the anon lists and how much we scan the file lists.  The big
policy changes are in separate patches.

[[email protected]: collect lru meminfo statistics from correct offset]
[[email protected]: prevent incorrect oom under split_lru]
[[email protected]: fix pagevec_move_tail() doesn't treat unevictable page]
[[email protected]: memcg swapbacked pages active]
[[email protected]: splitlru: BDI_CAP_SWAP_BACKED]
[[email protected]: fix /proc/vmstat units]
[[email protected]: memcg: fix handling of shmem migration]
[[email protected]: adjust Quicklists field of /proc/meminfo]
[[email protected]: fix style issue of get_scan_ratio()]
Signed-off-by: Rik van Riel <[email protected]>
Signed-off-by: Lee Schermerhorn <[email protected]>
Signed-off-by: KOSAKI Motohiro <[email protected]>
Signed-off-by: Hugh Dickins <[email protected]>
Signed-off-by: Daisuke Nishimura <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>