cfq-iosched: fold cfq_find_alloc_queue() into cfq_get_queue()

cfq_find_alloc_queue() checks whether a queue actually needs to be
allocated, which is unnecessary as its sole caller, cfq_get_queue(),
only calls it if so.  Also, the oom queue fallback logic is scattered
between cfq_get_queue() and cfq_find_alloc_queue().  There really
isn't much going on in the latter and things can be made simpler by
folding it into cfq_get_queue().

This patch collapses cfq_find_alloc_queue() into cfq_get_queue().  The
change is fairly straight-forward with one exception - async_cfqq is
now initialized to NULL and the "!is_sync" test in the last if
conditional is replaced with "async_cfqq" test.  This is because gcc
(5.1.1) gets confused for some reason and warns that async_cfqq may be
used uninitialized otherwise.  Oh well, the code isn't necessarily
worse this way.

This patch doesn't cause any functional difference.

v2: Updated to reflect GFP_ATOMIC -> GPF_NOWAIT.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Arianna Avanzini <avanzini.arianna@gmail.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index f3ea8a198deff06c03b386e983f3f4fa4e87ab7e..fa2a2f7dbecd5a52e3d7794d609ca8df4d6d711e 100644 (file)
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -3640,33 +3640,6 @@ static void check_blkcg_changed(struct cfq_io_cq *cic, struct bio *bio)
 static inline void check_blkcg_changed(struct cfq_io_cq *cic, struct bio *bio) { }
 #endif  /* CONFIG_CFQ_GROUP_IOSCHED */
 
-static struct cfq_queue *
-cfq_find_alloc_queue(struct cfq_data *cfqd, struct cfq_group *cfqg, bool is_sync,
-                    struct cfq_io_cq *cic, struct bio *bio)
-{
-       struct cfq_queue *cfqq;
-
-       cfqq = cic_to_cfqq(cic, is_sync);
-
-       /*
-        * Always try a new alloc if we fell back to the OOM cfqq
-        * originally, since it should just be a temporary situation.
-        */
-       if (!cfqq || cfqq == &cfqd->oom_cfqq) {
-               cfqq = kmem_cache_alloc_node(cfq_pool,
-                                            GFP_NOWAIT | __GFP_ZERO,
-                                            cfqd->queue->node);
-               if (cfqq) {
-                       cfq_init_cfqq(cfqd, cfqq, current->pid, is_sync);
-                       cfq_init_prio_data(cfqq, cic);
-                       cfq_link_cfqq_cfqg(cfqq, cfqg);
-                       cfq_log_cfqq(cfqd, cfqq, "alloced");
-               } else
-                       cfqq = &cfqd->oom_cfqq;
-       }
-       return cfqq;
-}
-
 static struct cfq_queue **
 cfq_async_queue_prio(struct cfq_data *cfqd, int ioprio_class, int ioprio)
 {
@@ -3691,7 +3664,7 @@ cfq_get_queue(struct cfq_data *cfqd, bool is_sync, struct cfq_io_cq *cic,
 {
        int ioprio_class = IOPRIO_PRIO_CLASS(cic->ioprio);
        int ioprio = IOPRIO_PRIO_DATA(cic->ioprio);
-       struct cfq_queue **async_cfqq;
+       struct cfq_queue **async_cfqq = NULL;
        struct cfq_queue *cfqq;
        struct cfq_group *cfqg;
 
@@ -3714,12 +3687,20 @@ cfq_get_queue(struct cfq_data *cfqd, bool is_sync, struct cfq_io_cq *cic,
                        goto out;
        }
 
-       cfqq = cfq_find_alloc_queue(cfqd, cfqg, is_sync, cic, bio);
+       cfqq = kmem_cache_alloc_node(cfq_pool, GFP_NOWAIT | __GFP_ZERO,
+                                    cfqd->queue->node);
+       if (!cfqq) {
+               cfqq = &cfqd->oom_cfqq;
+               goto out;
+       }
+
+       cfq_init_cfqq(cfqd, cfqq, current->pid, is_sync);
+       cfq_init_prio_data(cfqq, cic);
+       cfq_link_cfqq_cfqg(cfqq, cfqg);
+       cfq_log_cfqq(cfqd, cfqq, "alloced");
 
-       /*
-        * pin the queue now that it's allocated, scheduler exit will prune it
-        */
-       if (!is_sync && cfqq != &cfqd->oom_cfqq) {
+       if (async_cfqq) {
+               /* a new async queue is created, pin and remember */
                cfqq->ref++;
                *async_cfqq = cfqq;
        }
@@ -4469,7 +4450,7 @@ static int cfq_init_queue(struct request_queue *q, struct elevator_type *e)
                cfqd->prio_trees[i] = RB_ROOT;
 
        /*
-        * Our fallback cfqq if cfq_find_alloc_queue() runs into OOM issues.
+        * Our fallback cfqq if cfq_get_queue() runs into OOM issues.
         * Grab a permanent reference to it, so that the normal code flow
         * will not attempt to free it.  oom_cfqq is linked to root_group
         * but shouldn't hold a reference as it'll never be unlinked.  Lose