mm/vmscan: store "priority" in struct scan_control

In memory reclaim some function have too many arguments - "priority" is
one of them.  It can be stored in struct scan_control - we construct them
on the same level.  Instead of an open coded loop we set the initial
sc.priority, and do_try_to_free_pages() decreases it down to zero.

Change-Id: I7c03b4367fe3787dfd82afe1ff21469a99bdb04f
Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Git-commit: 9e3b2f8cd340e13353a44c9a34caef2848131ed7
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>
Signed-off-by: franciscofranco <franciscofranco.1990@gmail.com>