md: add proper merge_bvec handling to RAID0 and Linear.
These personalities currently set a max request size of one page
when any member device has a merge_bvec_fn because they don't
bother to call that function.
This causes extra works in splitting and combining requests.
So make the extra effort to call the merge_bvec_fn when it exists
so that we end up with larger requests out the bottom.
Signed-off-by: NeilBrown <neilb@suse.de>
diff --git a/drivers/md/linear.c b/drivers/md/linear.c
index 6794074..b0fcc7d 100644
--- a/drivers/md/linear.c
+++ b/drivers/md/linear.c
@@ -68,10 +68,19 @@
struct dev_info *dev0;
unsigned long maxsectors, bio_sectors = bvm->bi_size >> 9;
sector_t sector = bvm->bi_sector + get_start_sect(bvm->bi_bdev);
+ int maxbytes = biovec->bv_len;
+ struct request_queue *subq;
rcu_read_lock();
dev0 = which_dev(mddev, sector);
maxsectors = dev0->end_sector - sector;
+ subq = bdev_get_queue(dev0->rdev->bdev);
+ if (subq->merge_bvec_fn) {
+ bvm->bi_bdev = dev0->rdev->bdev;
+ bvm->bi_sector -= dev0->end_sector - dev0->rdev->sectors;
+ maxbytes = min(maxbytes, subq->merge_bvec_fn(subq, bvm,
+ biovec));
+ }
rcu_read_unlock();
if (maxsectors < bio_sectors)
@@ -80,12 +89,12 @@
maxsectors -= bio_sectors;
if (maxsectors <= (PAGE_SIZE >> 9 ) && bio_sectors == 0)
- return biovec->bv_len;
- /* The bytes available at this offset could be really big,
- * so we cap at 2^31 to avoid overflow */
- if (maxsectors > (1 << (31-9)))
- return 1<<31;
- return maxsectors << 9;
+ return maxbytes;
+
+ if (maxsectors > (maxbytes >> 9))
+ return maxbytes;
+ else
+ return maxsectors << 9;
}
static int linear_congested(void *data, int bits)
@@ -158,15 +167,6 @@
disk_stack_limits(mddev->gendisk, rdev->bdev,
rdev->data_offset << 9);
- /* as we don't honour merge_bvec_fn, we must never risk
- * violating it, so limit max_segments to 1 lying within
- * a single page.
- */
- if (rdev->bdev->bd_disk->queue->merge_bvec_fn) {
- blk_queue_max_segments(mddev->queue, 1);
- blk_queue_segment_boundary(mddev->queue,
- PAGE_CACHE_SIZE - 1);
- }
conf->array_sectors += rdev->sectors;
cnt++;