workqueue: add and use WQ_MEM_RECLAIM flag

Add WQ_MEM_RECLAIM flag which currently maps to WQ_RESCUER, mark
WQ_RESCUER as internal and replace all external WQ_RESCUER usages to
WQ_MEM_RECLAIM.

This makes the API users express the intent of the workqueue instead
of indicating the internal mechanism used to guarantee forward
progress.  This is also to make it cleaner to add more semantics to
WQ_MEM_RECLAIM.  For example, if deemed necessary, memory reclaim
workqueues can be made highpri.

This patch doesn't introduce any functional change.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Jeff Garzik <jgarzik@pobox.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Steven Whitehouse <swhiteho@redhat.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index b57a8babdec3..2c6871cbcbee 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -2848,6 +2848,13 @@ struct workqueue_struct *__alloc_workqueue_key(const char *name,
         unsigned int cpu;
 
         /*
+         * Workqueues which may be used during memory reclaim should
+         * have a rescuer to guarantee forward progress.
+         */
+        if (flags & WQ_MEM_RECLAIM)
+                flags |= WQ_RESCUER;
+
+        /*
          * Unbound workqueues aren't concurrency managed and should be
          * dispatched to workers immediately.
          */