Revert "mm: batch activate_page() to reduce lock contention"

Revert "mm: batch activate_page() to reduce lock contention"

This reverts commit 8054325847335d277052dc796431cb491c218f74.

Chris Mason ended up chasing down some page allocation errors and pages
stuck waiting on the IO scheduler, and was able to narrow it down to two
commits: commit 805432584733 ("mm: batch activate_page() to reduce lock
contention") and 87703ec3f0f3 ("mm: simplify code of swap.c").

This reverts the first of them.

Reported-and-debugged-by: Chris Mason <chris.mason@oracle.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jens Axboe <jaxboe@fusionio.com>
Cc: linux-mm <linux-mm@kvack.org>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Shaohua Li <shaohua.li@intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>