mm/zswap: improve with alloc_workqueue() call

The core-api create_workqueue is deprecated, this patch replaces the
create_workqueue with alloc_workqueue. The previous implementation
workqueue of zswap was a bounded workqueue, this patch uses
alloc_workqueue() to create an unbounded workqueue. The WQ_UNBOUND
attribute is desirable making the workqueue not localized to a specific
cpu so that the scheduler is free to exercise improvisations in any
demanding scenarios for offloading cpu time slices for workqueues. For
example if any other workqueues of the same primary cpu had to be served
which are WQ_HIGHPRI and WQ_CPU_INTENSIVE. Also Unbound workqueue happens
to be more efficient in a system during memory pressure scenarios in
comparison to a bounded workqueue.

shrink_wq = alloc_workqueue("zswap-shrink",
WQ_UNBOUND|WQ_MEM_RECLAIM, 1);

Overall the change suggested in this patch should be seamless and does not
alter the existing behavior, other than the improvisation to be an
unbounded workqueue.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Ronald Monthero <[e-mail]>
Acked-by: Nhat Pham <[e-mail]>
Acked-by: Johannes Weiner <[e-mail]>
Cc: Chris Li <[e-mail]>
Cc: Dan Streetman <[e-mail]>
Cc: Seth Jennings <[e-mail]>
Cc: Vitaly Wool <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

mm/zswap.c

···
 		zswap_enabled = false;
 	}
 
-	shrink_wq = create_workqueue("zswap-shrink");
+	shrink_wq = alloc_workqueue("zswap-shrink",
+			WQ_UNBOUND|WQ_MEM_RECLAIM, 1);
 	if (!shrink_wq)
 		goto fallback_fail;