[PATCH] pktcdvd: bio write congestion using congestion_wait()

This adds a bio write queue congestion control to the pktcdvd driver with
fixed on/off marks.  It prevents that the driver consumes a unlimited
amount of write requests.

[akpm@osdl.org: sync with congestion_wait() renaming]
Signed-off-by: Thomas Maier <balagi@justmail.de>
Cc: Peter Osterlund <petero2@telia.com>
Cc: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 41 insertions, 0 deletions

diff --git a/drivers/block/pktcdvd.c b/drivers/block/pktcdvd.c
index 7e7b892f621a..91fbe7fd6d0b 100644
--- a/drivers/block/pktcdvd.c
+++ b/drivers/block/pktcdvd.c
@@ -84,6 +84,8 @@
 static struct pktcdvd_device *pkt_devs[MAX_WRITERS];
 static struct proc_dir_entry *pkt_proc;
 static int pktdev_major;
+static int write_congestion_on  = PKT_WRITE_CONGESTION_ON;
+static int write_congestion_off = PKT_WRITE_CONGESTION_OFF;
 static struct mutex ctl_mutex;  /* Serialize open/close/setup/teardown */
 static mempool_t *psd_pool;
 
@@ -894,6 +896,7 @@ static int pkt_handle_queue(struct pktcdvd_device *pd)
         sector_t zone = 0; /* Suppress gcc warning */
         struct pkt_rb_node *node, *first_node;
         struct rb_node *n;
+        int wakeup;
 
         VPRINTK("handle_queue\n");
 
@@ -966,7 +969,13 @@ try_next_bio:
                 pkt->write_size += bio->bi_size / CD_FRAMESIZE;
                 spin_unlock(&pkt->lock);
         }
+        /* check write congestion marks, and if bio_queue_size is
+           below, wake up any waiters */
+        wakeup = (pd->write_congestion_on > 0
+                        && pd->bio_queue_size <= pd->write_congestion_off);
         spin_unlock(&pd->lock);
+        if (wakeup)
+                blk_clear_queue_congested(pd->disk->queue, WRITE);
 
         pkt->sleep_time = max(PACKET_WAIT_TIME, 1);
         pkt_set_state(pkt, PACKET_WAITING_STATE);
@@ -2179,6 +2188,23 @@ static int pkt_make_request(request_queue_t *q, struct bio *bio)
         }
         spin_unlock(&pd->cdrw.active_list_lock);
 
+        /*
+         * Test if there is enough room left in the bio work queue
+         * (queue size >= congestion on mark).
+         * If not, wait till the work queue size is below the congestion off mark.
+         */
+        spin_lock(&pd->lock);
+        if (pd->write_congestion_on > 0
+            && pd->bio_queue_size >= pd->write_congestion_on) {
+                blk_set_queue_congested(q, WRITE);
+                do {
+                        spin_unlock(&pd->lock);
+                        congestion_wait(WRITE, HZ);
+                        spin_lock(&pd->lock);
+                } while(pd->bio_queue_size > pd->write_congestion_off);
+        }
+        spin_unlock(&pd->lock);
+
         /*
          * No matching packet found. Store the bio in the work queue.
          */
@@ -2298,6 +2324,9 @@ static int pkt_seq_show(struct seq_file *m, void *p)
         seq_printf(m, "\tstate:\t\t\ti:%d ow:%d rw:%d ww:%d rec:%d fin:%d\n",
                    states[0], states[1], states[2], states[3], states[4], states[5]);
 
+        seq_printf(m, "\twrite congestion marks:\toff=%d on=%d\n",
+                        pd->write_congestion_off,
+                        pd->write_congestion_on);
         return 0;
 }
 
@@ -2474,6 +2503,9 @@ static int pkt_setup_dev(dev_t dev, dev_t* pkt_dev)
         init_waitqueue_head(&pd->wqueue);
         pd->bio_queue = RB_ROOT;
 
+        pd->write_congestion_on  = write_congestion_on;
+        pd->write_congestion_off = write_congestion_off;
+
         disk = alloc_disk(1);
         if (!disk)
                 goto out_mem;
diff --git a/include/linux/pktcdvd.h b/include/linux/pktcdvd.h
index 8a94c717c266..9b1a185fb1e5 100644
--- a/include/linux/pktcdvd.h
+++ b/include/linux/pktcdvd.h
@@ -112,6 +112,12 @@ struct pkt_ctrl_command {
 #include <linux/completion.h>
 #include <linux/cdrom.h>
 
+
+/* default bio write queue congestion marks */
+#define PKT_WRITE_CONGESTION_ON    10000
+#define PKT_WRITE_CONGESTION_OFF   9000
+
+
 struct packet_settings
 {
         __u32                   size;           /* packet size in (512 byte) sectors */
@@ -271,6 +277,9 @@ struct pktcdvd_device
 
         struct packet_iosched   iosched;
         struct gendisk          *disk;
+
+        int                     write_congestion_off;
+        int                     write_congestion_on;
 };
 
 #endif /* __KERNEL__ */