mm/workingset.c: refactor workingset_init()

Use prealloc_shrinker()/register_shrinker_prepared() instead of
register_shrinker().  This will be used in next patch.

[ktkhai@virtuozzo.com: v9]
  Link: http://lkml.kernel.org/r/153112550112.4097.16606173020912323761.stgit@localhost.localdomain
Link: http://lkml.kernel.org/r/153063057666.1818.17625951186610808734.stgit@localhost.localdomain
Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Acked-by: Vladimir Davydov <vdavydov.dev@gmail.com>
Tested-by: Shakeel Butt <shakeelb@google.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Josef Bacik <jbacik@fb.com>
Cc: Li RongQing <lirongqing@baidu.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Matthias Kaehlcke <mka@chromium.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Philippe Ombredanne <pombredanne@nexb.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Sahitya Tummala <stummala@codeaurora.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Waiman Long <longman@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/workingset.c

@@ -523,15 +523,16 @@ static int __init workingset_init(void)
 	pr_info("workingset: timestamp_bits=%d max_order=%d bucket_order=%u\n",
 	       timestamp_bits, max_order, bucket_order);
 
-	ret = __list_lru_init(&shadow_nodes, true, &shadow_nodes_key);
+	ret = prealloc_shrinker(&workingset_shadow_shrinker);
 	if (ret)
 		goto err;
-	ret = register_shrinker(&workingset_shadow_shrinker);
+	ret = __list_lru_init(&shadow_nodes, true, &shadow_nodes_key);
 	if (ret)
 		goto err_list_lru;
+	register_shrinker_prepared(&workingset_shadow_shrinker);
 	return 0;
 err_list_lru:
-	list_lru_destroy(&shadow_nodes);
+	free_prealloced_shrinker(&workingset_shadow_shrinker);
 err:
 	return ret;
 }