mm: use pagevec to rotate reclaimable page

While running some memory intensive load, system response deteriorated just
after swap-out started.

The cause of this problem is that when a PG_reclaim page is moved to the tail
of the inactive LRU list in rotate_reclaimable_page(), lru_lock spin lock is
acquired every page writeback .  This deteriorates system performance and
makes interrupt hold off time longer when swap-out started.

Following patch solves this problem.  I use pagevec in rotating reclaimable
pages to mitigate LRU spin lock contention and reduce interrupt hold off time.

I did a test that allocating and touching pages in multiple processes, and
pinging to the test machine in flooding mode to measure response under memory
intensive load.

The test result is:

	-2.6.23-rc5
	--- testmachine ping statistics ---
	3000 packets transmitted, 3000 received, 0% packet loss, time 53222ms
	rtt min/avg/max/mdev = 0.074/0.652/172.228/7.176 ms, pipe 11, ipg/ewma
17.746/0.092 ms

	-2.6.23-rc5-patched
	--- tes...