block: simplify force plug flush code a little bit

Cleaning up the code a little bit. attempt_plug_merge() traverses the plug
list anyway, we can do the request counting there, so stack size is reduced
a little bit.
The motivation here is I suspect if we should count the requests for each
queue (task could handle multiple disks in the meantime), but my test doesn't
show it's worthy doing. If somebody proves we should do it, below change
will make that more easier.

Signed-off-by: Shaohua Li <shli@kernel.org>
Signed-off-by: Shaohua Li <shaohua.li@intel.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

diff --git a/block/blk-core.c b/block/blk-core.c
index 67dba6941194d5a7b697c8bad2ccb89f11263682..b2ed78afd9f0cdeec0c313e751bd747df97eda92 100644 (file)
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1167,7 +1167,7 @@ static bool bio_attempt_front_merge(struct request_queue *q,
  * true if merge was successful, otherwise false.
  */
 static bool attempt_plug_merge(struct task_struct *tsk, struct request_queue *q,
-                              struct bio *bio)
+                              struct bio *bio, unsigned int *request_count)
 {
        struct blk_plug *plug;
        struct request *rq;
@@ -1176,10 +1176,13 @@ static bool attempt_plug_merge(struct task_struct *tsk, struct request_queue *q,
        plug = tsk->plug;
        if (!plug)
                goto out;
+       *request_count = 0;
 
        list_for_each_entry_reverse(rq, &plug->list, queuelist) {
                int el_ret;
 
+               (*request_count)++;
+
                if (rq->q != q)
                        continue;
 
@@ -1219,6 +1222,7 @@ static int __make_request(struct request_queue *q, struct bio *bio)
        struct blk_plug *plug;
        int el_ret, rw_flags, where = ELEVATOR_INSERT_SORT;
        struct request *req;
+       unsigned int request_count = 0;
 
        /*
         * low level driver can indicate that it wants pages above a
@@ -1237,7 +1241,7 @@ static int __make_request(struct request_queue *q, struct bio *bio)
         * Check if we can merge with the plugged list before grabbing
         * any locks.
         */
-       if (attempt_plug_merge(current, q, bio))
+       if (attempt_plug_merge(current, q, bio, &request_count))
                goto out;
 
        spin_lock_irq(q->queue_lock);
@@ -1302,9 +1306,8 @@ get_rq:
                        if (__rq->q != q)
                                plug->should_sort = 1;
                }
-               if (plug->count >= BLK_MAX_REQUEST_COUNT)
+               if (request_count >= BLK_MAX_REQUEST_COUNT)
                        blk_flush_plug_list(plug, false);
-               plug->count++;
                list_add_tail(&req->queuelist, &plug->list);
                drive_stat_acct(req, 1);
        } else {
@@ -2634,7 +2637,6 @@ void blk_start_plug(struct blk_plug *plug)
        INIT_LIST_HEAD(&plug->list);
        INIT_LIST_HEAD(&plug->cb_list);
        plug->should_sort = 0;
-       plug->count = 0;
 
        /*
         * If this is a nested plug, don't actually assign it. It will be
@@ -2718,7 +2720,6 @@ void blk_flush_plug_list(struct blk_plug *plug, bool from_schedule)
                return;
 
        list_splice_init(&plug->list, &list);
-       plug->count = 0;
 
        if (plug->should_sort) {
                list_sort(NULL, &list, plug_rq_cmp);

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 84b15d54f8c23887aef4600dd6f87fed0a99104e..7fbaa9103344a261082afd872127f736abdcd56f 100644 (file)
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -873,7 +873,6 @@ struct blk_plug {
        struct list_head list;
        struct list_head cb_list;
        unsigned int should_sort;
-       unsigned int count;
 };
 #define BLK_MAX_REQUEST_COUNT 16