xen/blkback: Seperate the bio allocation and the bio submission.
We seperate the bio allocation (bio_alloc) from the bio submission so
that the error paths are much easier, and also so that the bio
submission can be done in one tight loop. It also makes the
plug/unplug calls much much easier.
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
diff --git a/drivers/xen/blkback/blkback.c b/drivers/xen/blkback/blkback.c
index 464f2e0..3c10499 100644
--- a/drivers/xen/blkback/blkback.c
+++ b/drivers/xen/blkback/blkback.c
@@ -421,7 +421,8 @@
} seg[BLKIF_MAX_SEGMENTS_PER_REQUEST];
unsigned int nseg;
struct bio *bio = NULL;
- int ret, i;
+ struct bio *biolist[BLKIF_MAX_SEGMENTS_PER_REQUEST];
+ int ret, i, nbio = 0;
int operation;
struct blk_plug plug;
struct request_queue *q;
@@ -529,14 +530,7 @@
goto fail_flush;
}
- /* Get a reference count for the disk queue and start sending I/O */
- blk_get_queue(q);
- blk_start_plug(&plug);
-
- /* We set it one so that the last submit_bio does not have to call
- * atomic_inc.
- */
- atomic_set(&pending_req->pendcnt, 1);
+ /* This corresponding blkif_put is done in __end_block_io_op */
blkif_get(blkif);
for (i = 0; i < nseg; i++) {
@@ -552,12 +546,8 @@
blkbk->pending_page(pending_req, i),
seg[i].nsec << 9,
seg[i].buf & ~PAGE_MASK) == 0)) {
- if (bio) {
- atomic_inc(&pending_req->pendcnt);
- submit_bio(operation, bio);
- }
- bio = bio_alloc(GFP_KERNEL, nseg-i);
+ bio = biolist[nbio++] = bio_alloc(GFP_KERNEL, nseg-i);
if (unlikely(bio == NULL))
goto fail_put_bio;
@@ -573,7 +563,7 @@
/* This will be hit if the operation was a barrier. */
if (!bio) {
BUG_ON(operation != WRITE_BARRIER);
- bio = bio_alloc(GFP_KERNEL, 0);
+ bio = biolist[nbio++] = bio_alloc(GFP_KERNEL, 0);
if (unlikely(bio == NULL))
goto fail_put_bio;
@@ -583,15 +573,28 @@
bio->bi_sector = -1;
}
- submit_bio(operation, bio);
+
+ /* We set it one so that the last submit_bio does not have to call
+ * atomic_inc.
+ */
+ atomic_set(&pending_req->pendcnt, nbio);
+
+ /* Get a reference count for the disk queue and start sending I/O */
+ blk_get_queue(q);
+ blk_start_plug(&plug);
+
+ for (i = 0; i < nbio; i++)
+ submit_bio(operation, biolist[i]);
+
+ blk_finish_plug(&plug);
+ /* Let the I/Os go.. */
+ blk_put_queue(q);
if (operation == READ)
blkif->st_rd_sect += preq.nr_sects;
else if (operation == WRITE || operation == WRITE_BARRIER)
blkif->st_wr_sect += preq.nr_sects;
- blk_finish_plug(&plug);
- blk_put_queue(q);
return;
fail_flush:
@@ -604,11 +607,9 @@
return;
fail_put_bio:
+ for (i = 0; i < (nbio-1); i++)
+ bio_put(biolist[i]);
__end_block_io_op(pending_req, -EINVAL);
- if (bio)
- bio_put(bio);
- blk_finish_plug(&plug);
- blk_put_queue(q);
msleep(1); /* back off a bit */
return;
}