block: Initial support for data-less (or empty) barrier support
This implements functionality to pass down or insert a barrier
in a queue, without having data attached to it. The ->prepare_flush_fn()
infrastructure from data barriers are reused to provide this
functionality.
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/block/elevator.c b/block/elevator.c
index ec23ca0..952aee0 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -712,6 +712,14 @@
int ret;
while ((rq = __elv_next_request(q)) != NULL) {
+ /*
+ * Kill the empty barrier place holder, the driver must
+ * not ever see it.
+ */
+ if (blk_empty_barrier(rq)) {
+ end_queued_request(rq, 1);
+ continue;
+ }
if (!(rq->cmd_flags & REQ_STARTED)) {
/*
* This is the first time the device driver
diff --git a/block/ll_rw_blk.c b/block/ll_rw_blk.c
index 548f0d8..4fde3a3 100644
--- a/block/ll_rw_blk.c
+++ b/block/ll_rw_blk.c
@@ -458,9 +458,12 @@
* Queue ordered sequence. As we stack them at the head, we
* need to queue in reverse order. Note that we rely on that
* no fs request uses ELEVATOR_INSERT_FRONT and thus no fs
- * request gets inbetween ordered sequence.
+ * request gets inbetween ordered sequence. If this request is
+ * an empty barrier, we don't need to do a postflush ever since
+ * there will be no data written between the pre and post flush.
+ * Hence a single flush will suffice.
*/
- if (q->ordered & QUEUE_ORDERED_POSTFLUSH)
+ if ((q->ordered & QUEUE_ORDERED_POSTFLUSH) && !blk_empty_barrier(rq))
queue_flush(q, QUEUE_ORDERED_POSTFLUSH);
else
q->ordseq |= QUEUE_ORDSEQ_POSTFLUSH;
@@ -484,7 +487,7 @@
int blk_do_ordered(struct request_queue *q, struct request **rqp)
{
struct request *rq = *rqp;
- int is_barrier = blk_fs_request(rq) && blk_barrier_rq(rq);
+ const int is_barrier = blk_fs_request(rq) && blk_barrier_rq(rq);
if (!q->ordseq) {
if (!is_barrier)
@@ -3054,7 +3057,7 @@
{
struct block_device *bdev = bio->bi_bdev;
- if (bdev != bdev->bd_contains) {
+ if (bio_sectors(bio) && bdev != bdev->bd_contains) {
struct hd_struct *p = bdev->bd_part;
const int rw = bio_data_dir(bio);
@@ -3313,23 +3316,32 @@
{
int count = bio_sectors(bio);
- BIO_BUG_ON(!bio->bi_size);
- BIO_BUG_ON(!bio->bi_io_vec);
bio->bi_rw |= rw;
- if (rw & WRITE) {
- count_vm_events(PGPGOUT, count);
- } else {
- task_io_account_read(bio->bi_size);
- count_vm_events(PGPGIN, count);
- }
- if (unlikely(block_dump)) {
- char b[BDEVNAME_SIZE];
- printk(KERN_DEBUG "%s(%d): %s block %Lu on %s\n",
- current->comm, current->pid,
- (rw & WRITE) ? "WRITE" : "READ",
- (unsigned long long)bio->bi_sector,
- bdevname(bio->bi_bdev,b));
+ /*
+ * If it's a regular read/write or a barrier with data attached,
+ * go through the normal accounting stuff before submission.
+ */
+ if (!bio_empty_barrier(bio)) {
+
+ BIO_BUG_ON(!bio->bi_size);
+ BIO_BUG_ON(!bio->bi_io_vec);
+
+ if (rw & WRITE) {
+ count_vm_events(PGPGOUT, count);
+ } else {
+ task_io_account_read(bio->bi_size);
+ count_vm_events(PGPGIN, count);
+ }
+
+ if (unlikely(block_dump)) {
+ char b[BDEVNAME_SIZE];
+ printk(KERN_DEBUG "%s(%d): %s block %Lu on %s\n",
+ current->comm, current->pid,
+ (rw & WRITE) ? "WRITE" : "READ",
+ (unsigned long long)bio->bi_sector,
+ bdevname(bio->bi_bdev,b));
+ }
}
generic_make_request(bio);
@@ -3405,6 +3417,14 @@
while ((bio = req->bio) != NULL) {
int nbytes;
+ /*
+ * For an empty barrier request, the low level driver must
+ * store a potential error location in ->sector. We pass
+ * that back up in ->bi_sector.
+ */
+ if (blk_empty_barrier(req))
+ bio->bi_sector = req->sector;
+
if (nr_bytes >= bio->bi_size) {
req->bio = bio->bi_next;
nbytes = bio->bi_size;
diff --git a/include/linux/bio.h b/include/linux/bio.h
index 089a8bc..4da4413 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -176,13 +176,28 @@
#define bio_offset(bio) bio_iovec((bio))->bv_offset
#define bio_segments(bio) ((bio)->bi_vcnt - (bio)->bi_idx)
#define bio_sectors(bio) ((bio)->bi_size >> 9)
-#define bio_cur_sectors(bio) (bio_iovec(bio)->bv_len >> 9)
-#define bio_data(bio) (page_address(bio_page((bio))) + bio_offset((bio)))
#define bio_barrier(bio) ((bio)->bi_rw & (1 << BIO_RW_BARRIER))
#define bio_sync(bio) ((bio)->bi_rw & (1 << BIO_RW_SYNC))
#define bio_failfast(bio) ((bio)->bi_rw & (1 << BIO_RW_FAILFAST))
#define bio_rw_ahead(bio) ((bio)->bi_rw & (1 << BIO_RW_AHEAD))
#define bio_rw_meta(bio) ((bio)->bi_rw & (1 << BIO_RW_META))
+#define bio_empty_barrier(bio) (bio_barrier(bio) && !(bio)->bi_size)
+
+static inline unsigned int bio_cur_sectors(struct bio *bio)
+{
+ if (bio->bi_vcnt)
+ return bio_iovec(bio)->bv_len >> 9;
+
+ return 0;
+}
+
+static inline void *bio_data(struct bio *bio)
+{
+ if (bio->bi_vcnt)
+ return page_address(bio_page(bio)) + bio_offset(bio);
+
+ return NULL;
+}
/*
* will die
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 6109679..fb2ff74 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -540,6 +540,7 @@
#define blk_barrier_rq(rq) ((rq)->cmd_flags & REQ_HARDBARRIER)
#define blk_fua_rq(rq) ((rq)->cmd_flags & REQ_FUA)
#define blk_bidi_rq(rq) ((rq)->next_rq != NULL)
+#define blk_empty_barrier(rq) (blk_barrier_rq(rq) && blk_fs_request(rq) && !(rq)->hard_nr_sectors)
#define list_entry_rq(ptr) list_entry((ptr), struct request, queuelist)
diff --git a/mm/bounce.c b/mm/bounce.c
index 3b549bf..b6d2d0f 100644
--- a/mm/bounce.c
+++ b/mm/bounce.c
@@ -265,6 +265,12 @@
mempool_t *pool;
/*
+ * Data-less bio, nothing to bounce
+ */
+ if (bio_empty_barrier(*bio_orig))
+ return;
+
+ /*
* for non-isa bounce case, just check if the bounce pfn is equal
* to or bigger than the highest pfn in the system -- in that case,
* don't waste time iterating over bio segments