block: ll_rw_blk.c split, add blk-merge.c

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

4 files changed, 495 insertions, 481 deletions

diff --git a/block/Makefile b/block/Makefile
index 2002046..5a43c7d 100644
--- a/block/Makefile
+++ b/block/Makefile
@@ -4,7 +4,7 @@
 
 obj-$(CONFIG_BLOCK) := elevator.o blk-core.o blk-tag.o blk-sysfs.o \
 			blk-barrier.o blk-settings.o blk-ioc.o blk-map.o \
-			blk-exec.o ioctl.o genhd.o scsi_ioctl.o
+			blk-exec.o blk-merge.o ioctl.o genhd.o scsi_ioctl.o
 
 obj-$(CONFIG_BLK_DEV_BSG)	+= bsg.o
 obj-$(CONFIG_IOSCHED_NOOP)	+= noop-iosched.o
diff --git a/block/blk-core.c b/block/blk-core.c
index 99f4d64..8ff9944 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -29,7 +29,6 @@
 #include <linux/cpu.h>
 #include <linux/blktrace_api.h>
 #include <linux/fault-inject.h>
-#include <linux/scatterlist.h>
 
 #include "blk.h"
 
@@ -181,376 +180,6 @@ void blk_dump_rq_flags(struct request *rq, char *msg)
 
 EXPORT_SYMBOL(blk_dump_rq_flags);
 
-static void blk_recalc_rq_segments(struct request *rq)
-{
-	int nr_phys_segs;
-	int nr_hw_segs;
-	unsigned int phys_size;
-	unsigned int hw_size;
-	struct bio_vec *bv, *bvprv = NULL;
-	int seg_size;
-	int hw_seg_size;
-	int cluster;
-	struct req_iterator iter;
-	int high, highprv = 1;
-	struct request_queue *q = rq->q;
-
-	if (!rq->bio)
-		return;
-
-	cluster = q->queue_flags & (1 << QUEUE_FLAG_CLUSTER);
-	hw_seg_size = seg_size = 0;
-	phys_size = hw_size = nr_phys_segs = nr_hw_segs = 0;
-	rq_for_each_segment(bv, rq, iter) {
-		/*
-		 * the trick here is making sure that a high page is never
-		 * considered part of another segment, since that might
-		 * change with the bounce page.
-		 */
-		high = page_to_pfn(bv->bv_page) > q->bounce_pfn;
-		if (high || highprv)
-			goto new_hw_segment;
-		if (cluster) {
-			if (seg_size + bv->bv_len > q->max_segment_size)
-				goto new_segment;
-			if (!BIOVEC_PHYS_MERGEABLE(bvprv, bv))
-				goto new_segment;
-			if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bv))
-				goto new_segment;
-			if (BIOVEC_VIRT_OVERSIZE(hw_seg_size + bv->bv_len))
-				goto new_hw_segment;
-
-			seg_size += bv->bv_len;
-			hw_seg_size += bv->bv_len;
-			bvprv = bv;
-			continue;
-		}
-new_segment:
-		if (BIOVEC_VIRT_MERGEABLE(bvprv, bv) &&
-		    !BIOVEC_VIRT_OVERSIZE(hw_seg_size + bv->bv_len))
-			hw_seg_size += bv->bv_len;
-		else {
-new_hw_segment:
-			if (nr_hw_segs == 1 &&
-			    hw_seg_size > rq->bio->bi_hw_front_size)
-				rq->bio->bi_hw_front_size = hw_seg_size;
-			hw_seg_size = BIOVEC_VIRT_START_SIZE(bv) + bv->bv_len;
-			nr_hw_segs++;
-		}
-
-		nr_phys_segs++;
-		bvprv = bv;
-		seg_size = bv->bv_len;
-		highprv = high;
-	}
-
-	if (nr_hw_segs == 1 &&
-	    hw_seg_size > rq->bio->bi_hw_front_size)
-		rq->bio->bi_hw_front_size = hw_seg_size;
-	if (hw_seg_size > rq->biotail->bi_hw_back_size)
-		rq->biotail->bi_hw_back_size = hw_seg_size;
-	rq->nr_phys_segments = nr_phys_segs;
-	rq->nr_hw_segments = nr_hw_segs;
-}
-
-void blk_recount_segments(struct request_queue *q, struct bio *bio)
-{
-	struct request rq;
-	struct bio *nxt = bio->bi_next;
-	rq.q = q;
-	rq.bio = rq.biotail = bio;
-	bio->bi_next = NULL;
-	blk_recalc_rq_segments(&rq);
-	bio->bi_next = nxt;
-	bio->bi_phys_segments = rq.nr_phys_segments;
-	bio->bi_hw_segments = rq.nr_hw_segments;
-	bio->bi_flags |= (1 << BIO_SEG_VALID);
-}
-EXPORT_SYMBOL(blk_recount_segments);
-
-static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio,
-				   struct bio *nxt)
-{
-	if (!(q->queue_flags & (1 << QUEUE_FLAG_CLUSTER)))
-		return 0;
-
-	if (!BIOVEC_PHYS_MERGEABLE(__BVEC_END(bio), __BVEC_START(nxt)))
-		return 0;
-	if (bio->bi_size + nxt->bi_size > q->max_segment_size)
-		return 0;
-
-	/*
-	 * bio and nxt are contigous in memory, check if the queue allows
-	 * these two to be merged into one
-	 */
-	if (BIO_SEG_BOUNDARY(q, bio, nxt))
-		return 1;
-
-	return 0;
-}
-
-static int blk_hw_contig_segment(struct request_queue *q, struct bio *bio,
-				 struct bio *nxt)
-{
-	if (unlikely(!bio_flagged(bio, BIO_SEG_VALID)))
-		blk_recount_segments(q, bio);
-	if (unlikely(!bio_flagged(nxt, BIO_SEG_VALID)))
-		blk_recount_segments(q, nxt);
-	if (!BIOVEC_VIRT_MERGEABLE(__BVEC_END(bio), __BVEC_START(nxt)) ||
-	    BIOVEC_VIRT_OVERSIZE(bio->bi_hw_back_size + nxt->bi_hw_front_size))
-		return 0;
-	if (bio->bi_hw_back_size + nxt->bi_hw_front_size > q->max_segment_size)
-		return 0;
-
-	return 1;
-}
-
-/*
- * map a request to scatterlist, return number of sg entries setup. Caller
- * must make sure sg can hold rq->nr_phys_segments entries
- */
-int blk_rq_map_sg(struct request_queue *q, struct request *rq,
-		  struct scatterlist *sglist)
-{
-	struct bio_vec *bvec, *bvprv;
-	struct req_iterator iter;
-	struct scatterlist *sg;
-	int nsegs, cluster;
-
-	nsegs = 0;
-	cluster = q->queue_flags & (1 << QUEUE_FLAG_CLUSTER);
-
-	/*
-	 * for each bio in rq
-	 */
-	bvprv = NULL;
-	sg = NULL;
-	rq_for_each_segment(bvec, rq, iter) {
-		int nbytes = bvec->bv_len;
-
-		if (bvprv && cluster) {
-			if (sg->length + nbytes > q->max_segment_size)
-				goto new_segment;
-
-			if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec))
-				goto new_segment;
-			if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec))
-				goto new_segment;
-
-			sg->length += nbytes;
-		} else {
-new_segment:
-			if (!sg)
-				sg = sglist;
-			else {
-				/*
-				 * If the driver previously mapped a shorter
-				 * list, we could see a termination bit
-				 * prematurely unless it fully inits the sg
-				 * table on each mapping. We KNOW that there
-				 * must be more entries here or the driver
-				 * would be buggy, so force clear the
-				 * termination bit to avoid doing a full
-				 * sg_init_table() in drivers for each command.
-				 */
-				sg->page_link &= ~0x02;
-				sg = sg_next(sg);
-			}
-
-			sg_set_page(sg, bvec->bv_page, nbytes, bvec->bv_offset);
-			nsegs++;
-		}
-		bvprv = bvec;
-	} /* segments in rq */
-
-	if (q->dma_drain_size) {
-		sg->page_link &= ~0x02;
-		sg = sg_next(sg);
-		sg_set_page(sg, virt_to_page(q->dma_drain_buffer),
-			    q->dma_drain_size,
-			    ((unsigned long)q->dma_drain_buffer) &
-			    (PAGE_SIZE - 1));
-		nsegs++;
-	}
-
-	if (sg)
-		sg_mark_end(sg);
-
-	return nsegs;
-}
-
-EXPORT_SYMBOL(blk_rq_map_sg);
-
-static inline int ll_new_mergeable(struct request_queue *q,
-				   struct request *req,
-				   struct bio *bio)
-{
-	int nr_phys_segs = bio_phys_segments(q, bio);
-
-	if (req->nr_phys_segments + nr_phys_segs > q->max_phys_segments) {
-		req->cmd_flags |= REQ_NOMERGE;
-		if (req == q->last_merge)
-			q->last_merge = NULL;
-		return 0;
-	}
-
-	/*
-	 * A hw segment is just getting larger, bump just the phys
-	 * counter.
-	 */
-	req->nr_phys_segments += nr_phys_segs;
-	return 1;
-}
-
-static inline int ll_new_hw_segment(struct request_queue *q,
-				    struct request *req,
-				    struct bio *bio)
-{
-	int nr_hw_segs = bio_hw_segments(q, bio);
-	int nr_phys_segs = bio_phys_segments(q, bio);
-
-	if (req->nr_hw_segments + nr_hw_segs > q->max_hw_segments
-	    || req->nr_phys_segments + nr_phys_segs > q->max_phys_segments) {
-		req->cmd_flags |= REQ_NOMERGE;
-		if (req == q->last_merge)
-			q->last_merge = NULL;
-		return 0;
-	}
-
-	/*
-	 * This will form the start of a new hw segment.  Bump both
-	 * counters.
-	 */
-	req->nr_hw_segments += nr_hw_segs;
-	req->nr_phys_segments += nr_phys_segs;
-	return 1;
-}
-
-int ll_back_merge_fn(struct request_queue *q, struct request *req,
-		     struct bio *bio)
-{
-	unsigned short max_sectors;
-	int len;
-
-	if (unlikely(blk_pc_request(req)))
-		max_sectors = q->max_hw_sectors;
-	else
-		max_sectors = q->max_sectors;
-
-	if (req->nr_sectors + bio_sectors(bio) > max_sectors) {
-		req->cmd_flags |= REQ_NOMERGE;
-		if (req == q->last_merge)
-			q->last_merge = NULL;
-		return 0;
-	}
-	if (unlikely(!bio_flagged(req->biotail, BIO_SEG_VALID)))
-		blk_recount_segments(q, req->biotail);
-	if (unlikely(!bio_flagged(bio, BIO_SEG_VALID)))
-		blk_recount_segments(q, bio);
-	len = req->biotail->bi_hw_back_size + bio->bi_hw_front_size;
-	if (BIOVEC_VIRT_MERGEABLE(__BVEC_END(req->biotail), __BVEC_START(bio)) &&
-	    !BIOVEC_VIRT_OVERSIZE(len)) {
-		int mergeable =  ll_new_mergeable(q, req, bio);
-
-		if (mergeable) {
-			if (req->nr_hw_segments == 1)
-				req->bio->bi_hw_front_size = len;
-			if (bio->bi_hw_segments == 1)
-				bio->bi_hw_back_size = len;
-		}
-		return mergeable;
-	}
-
-	return ll_new_hw_segment(q, req, bio);
-}
-
-static int ll_front_merge_fn(struct request_queue *q, struct request *req, 
-			     struct bio *bio)
-{
-	unsigned short max_sectors;
-	int len;
-
-	if (unlikely(blk_pc_request(req)))
-		max_sectors = q->max_hw_sectors;
-	else
-		max_sectors = q->max_sectors;
-
-
-	if (req->nr_sectors + bio_sectors(bio) > max_sectors) {
-		req->cmd_flags |= REQ_NOMERGE;
-		if (req == q->last_merge)
-			q->last_merge = NULL;
-		return 0;
-	}
-	len = bio->bi_hw_back_size + req->bio->bi_hw_front_size;
-	if (unlikely(!bio_flagged(bio, BIO_SEG_VALID)))
-		blk_recount_segments(q, bio);
-	if (unlikely(!bio_flagged(req->bio, BIO_SEG_VALID)))
-		blk_recount_segments(q, req->bio);
-	if (BIOVEC_VIRT_MERGEABLE(__BVEC_END(bio), __BVEC_START(req->bio)) &&
-	    !BIOVEC_VIRT_OVERSIZE(len)) {
-		int mergeable =  ll_new_mergeable(q, req, bio);
-
-		if (mergeable) {
-			if (bio->bi_hw_segments == 1)
-				bio->bi_hw_front_size = len;
-			if (req->nr_hw_segments == 1)
-				req->biotail->bi_hw_back_size = len;
-		}
-		return mergeable;
-	}
-
-	return ll_new_hw_segment(q, req, bio);
-}
-
-static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
-				struct request *next)
-{
-	int total_phys_segments;
-	int total_hw_segments;
-
-	/*
-	 * First check if the either of the requests are re-queued
-	 * requests.  Can't merge them if they are.
-	 */
-	if (req->special || next->special)
-		return 0;
-
-	/*
-	 * Will it become too large?
-	 */
-	if ((req->nr_sectors + next->nr_sectors) > q->max_sectors)
-		return 0;
-
-	total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
-	if (blk_phys_contig_segment(q, req->biotail, next->bio))
-		total_phys_segments--;
-
-	if (total_phys_segments > q->max_phys_segments)
-		return 0;
-
-	total_hw_segments = req->nr_hw_segments + next->nr_hw_segments;
-	if (blk_hw_contig_segment(q, req->biotail, next->bio)) {
-		int len = req->biotail->bi_hw_back_size + next->bio->bi_hw_front_size;
-		/*
-		 * propagate the combined length to the end of the requests
-		 */
-		if (req->nr_hw_segments == 1)
-			req->bio->bi_hw_front_size = len;
-		if (next->nr_hw_segments == 1)
-			next->biotail->bi_hw_back_size = len;
-		total_hw_segments--;
-	}
-
-	if (total_hw_segments > q->max_hw_segments)
-		return 0;
-
-	/* Merge is OK... */
-	req->nr_phys_segments = total_phys_segments;
-	req->nr_hw_segments = total_hw_segments;
-	return 1;
-}
-
 /*
  * "plug" the device if there are no outstanding requests: this will
  * force the transfer to start only after we have put all the requests
@@ -1409,84 +1038,6 @@ void blk_put_request(struct request *req)
 
 EXPORT_SYMBOL(blk_put_request);
 
-/*
- * Has to be called with the request spinlock acquired
- */
-static int attempt_merge(struct request_queue *q, struct request *req,
-			  struct request *next)
-{
-	if (!rq_mergeable(req) || !rq_mergeable(next))
-		return 0;
-
-	/*
-	 * not contiguous
-	 */
-	if (req->sector + req->nr_sectors != next->sector)
-		return 0;
-
-	if (rq_data_dir(req) != rq_data_dir(next)
-	    || req->rq_disk != next->rq_disk
-	    || next->special)
-		return 0;
-
-	/*
-	 * If we are allowed to merge, then append bio list
-	 * from next to rq and release next. merge_requests_fn
-	 * will have updated segment counts, update sector
-	 * counts here.
-	 */
-	if (!ll_merge_requests_fn(q, req, next))
-		return 0;
-
-	/*
-	 * At this point we have either done a back merge
-	 * or front merge. We need the smaller start_time of
-	 * the merged requests to be the current request
-	 * for accounting purposes.
-	 */
-	if (time_after(req->start_time, next->start_time))
-		req->start_time = next->start_time;
-
-	req->biotail->bi_next = next->bio;
-	req->biotail = next->biotail;
-
-	req->nr_sectors = req->hard_nr_sectors += next->hard_nr_sectors;
-
-	elv_merge_requests(q, req, next);
-
-	if (req->rq_disk) {
-		disk_round_stats(req->rq_disk);
-		req->rq_disk->in_flight--;
-	}
-
-	req->ioprio = ioprio_best(req->ioprio, next->ioprio);
-
-	__blk_put_request(q, next);
-	return 1;
-}
-
-static inline int attempt_back_merge(struct request_queue *q,
-				     struct request *rq)
-{
-	struct request *next = elv_latter_request(q, rq);
-
-	if (next)
-		return attempt_merge(q, rq, next);
-
-	return 0;
-}
-
-static inline int attempt_front_merge(struct request_queue *q,
-				      struct request *rq)
-{
-	struct request *prev = elv_former_request(q, rq);
-
-	if (prev)
-		return attempt_merge(q, prev, rq);
-
-	return 0;
-}
-
 void init_request_from_bio(struct request *req, struct bio *bio)
 {
 	req->cmd_type = REQ_TYPE_FS;
@@ -1938,35 +1489,6 @@ void submit_bio(int rw, struct bio *bio)
 
 EXPORT_SYMBOL(submit_bio);
 
-static void blk_recalc_rq_sectors(struct request *rq, int nsect)
-{
-	if (blk_fs_request(rq)) {
-		rq->hard_sector += nsect;
-		rq->hard_nr_sectors -= nsect;
-
-		/*
-		 * Move the I/O submission pointers ahead if required.
-		 */
-		if ((rq->nr_sectors >= rq->hard_nr_sectors) &&
-		    (rq->sector <= rq->hard_sector)) {
-			rq->sector = rq->hard_sector;
-			rq->nr_sectors = rq->hard_nr_sectors;
-			rq->hard_cur_sectors = bio_cur_sectors(rq->bio);
-			rq->current_nr_sectors = rq->hard_cur_sectors;
-			rq->buffer = bio_data(rq->bio);
-		}
-
-		/*
-		 * if total number of sectors is less than the first segment
-		 * size, something has gone terribly wrong
-		 */
-		if (rq->nr_sectors < rq->current_nr_sectors) {
-			printk("blk: request botched\n");
-			rq->nr_sectors = rq->current_nr_sectors;
-		}
-	}
-}
-
 /**
  * __end_that_request_first - end I/O on a request
  * @req:      the request being processed
diff --git a/block/blk-merge.c b/block/blk-merge.c
new file mode 100644
index 0000000..5023f0b
--- /dev/null
+++ b/block/blk-merge.c
@@ -0,0 +1,485 @@
+/*
+ * Functions related to segment and merge handling
+ */
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/bio.h>
+#include <linux/blkdev.h>
+#include <linux/scatterlist.h>
+
+#include "blk.h"
+
+void blk_recalc_rq_sectors(struct request *rq, int nsect)
+{
+	if (blk_fs_request(rq)) {
+		rq->hard_sector += nsect;
+		rq->hard_nr_sectors -= nsect;
+
+		/*
+		 * Move the I/O submission pointers ahead if required.
+		 */
+		if ((rq->nr_sectors >= rq->hard_nr_sectors) &&
+		    (rq->sector <= rq->hard_sector)) {
+			rq->sector = rq->hard_sector;
+			rq->nr_sectors = rq->hard_nr_sectors;
+			rq->hard_cur_sectors = bio_cur_sectors(rq->bio);
+			rq->current_nr_sectors = rq->hard_cur_sectors;
+			rq->buffer = bio_data(rq->bio);
+		}
+
+		/*
+		 * if total number of sectors is less than the first segment
+		 * size, something has gone terribly wrong
+		 */
+		if (rq->nr_sectors < rq->current_nr_sectors) {
+			printk("blk: request botched\n");
+			rq->nr_sectors = rq->current_nr_sectors;
+		}
+	}
+}
+
+void blk_recalc_rq_segments(struct request *rq)
+{
+	int nr_phys_segs;
+	int nr_hw_segs;
+	unsigned int phys_size;
+	unsigned int hw_size;
+	struct bio_vec *bv, *bvprv = NULL;
+	int seg_size;
+	int hw_seg_size;
+	int cluster;
+	struct req_iterator iter;
+	int high, highprv = 1;
+	struct request_queue *q = rq->q;
+
+	if (!rq->bio)
+		return;
+
+	cluster = q->queue_flags & (1 << QUEUE_FLAG_CLUSTER);
+	hw_seg_size = seg_size = 0;
+	phys_size = hw_size = nr_phys_segs = nr_hw_segs = 0;
+	rq_for_each_segment(bv, rq, iter) {
+		/*
+		 * the trick here is making sure that a high page is never
+		 * considered part of another segment, since that might
+		 * change with the bounce page.
+		 */
+		high = page_to_pfn(bv->bv_page) > q->bounce_pfn;
+		if (high || highprv)
+			goto new_hw_segment;
+		if (cluster) {
+			if (seg_size + bv->bv_len > q->max_segment_size)
+				goto new_segment;
+			if (!BIOVEC_PHYS_MERGEABLE(bvprv, bv))
+				goto new_segment;
+			if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bv))
+				goto new_segment;
+			if (BIOVEC_VIRT_OVERSIZE(hw_seg_size + bv->bv_len))
+				goto new_hw_segment;
+
+			seg_size += bv->bv_len;
+			hw_seg_size += bv->bv_len;
+			bvprv = bv;
+			continue;
+		}
+new_segment:
+		if (BIOVEC_VIRT_MERGEABLE(bvprv, bv) &&
+		    !BIOVEC_VIRT_OVERSIZE(hw_seg_size + bv->bv_len))
+			hw_seg_size += bv->bv_len;
+		else {
+new_hw_segment:
+			if (nr_hw_segs == 1 &&
+			    hw_seg_size > rq->bio->bi_hw_front_size)
+				rq->bio->bi_hw_front_size = hw_seg_size;
+			hw_seg_size = BIOVEC_VIRT_START_SIZE(bv) + bv->bv_len;
+			nr_hw_segs++;
+		}
+
+		nr_phys_segs++;
+		bvprv = bv;
+		seg_size = bv->bv_len;
+		highprv = high;
+	}
+
+	if (nr_hw_segs == 1 &&
+	    hw_seg_size > rq->bio->bi_hw_front_size)
+		rq->bio->bi_hw_front_size = hw_seg_size;
+	if (hw_seg_size > rq->biotail->bi_hw_back_size)
+		rq->biotail->bi_hw_back_size = hw_seg_size;
+	rq->nr_phys_segments = nr_phys_segs;
+	rq->nr_hw_segments = nr_hw_segs;
+}
+
+void blk_recount_segments(struct request_queue *q, struct bio *bio)
+{
+	struct request rq;
+	struct bio *nxt = bio->bi_next;
+	rq.q = q;
+	rq.bio = rq.biotail = bio;
+	bio->bi_next = NULL;
+	blk_recalc_rq_segments(&rq);
+	bio->bi_next = nxt;
+	bio->bi_phys_segments = rq.nr_phys_segments;
+	bio->bi_hw_segments = rq.nr_hw_segments;
+	bio->bi_flags |= (1 << BIO_SEG_VALID);
+}
+EXPORT_SYMBOL(blk_recount_segments);
+
+static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio,
+				   struct bio *nxt)
+{
+	if (!(q->queue_flags & (1 << QUEUE_FLAG_CLUSTER)))
+		return 0;
+
+	if (!BIOVEC_PHYS_MERGEABLE(__BVEC_END(bio), __BVEC_START(nxt)))
+		return 0;
+	if (bio->bi_size + nxt->bi_size > q->max_segment_size)
+		return 0;
+
+	/*
+	 * bio and nxt are contigous in memory, check if the queue allows
+	 * these two to be merged into one
+	 */
+	if (BIO_SEG_BOUNDARY(q, bio, nxt))
+		return 1;
+
+	return 0;
+}
+
+static int blk_hw_contig_segment(struct request_queue *q, struct bio *bio,
+				 struct bio *nxt)
+{
+	if (unlikely(!bio_flagged(bio, BIO_SEG_VALID)))
+		blk_recount_segments(q, bio);
+	if (unlikely(!bio_flagged(nxt, BIO_SEG_VALID)))
+		blk_recount_segments(q, nxt);
+	if (!BIOVEC_VIRT_MERGEABLE(__BVEC_END(bio), __BVEC_START(nxt)) ||
+	    BIOVEC_VIRT_OVERSIZE(bio->bi_hw_back_size + nxt->bi_hw_front_size))
+		return 0;
+	if (bio->bi_hw_back_size + nxt->bi_hw_front_size > q->max_segment_size)
+		return 0;
+
+	return 1;
+}
+
+/*
+ * map a request to scatterlist, return number of sg entries setup. Caller
+ * must make sure sg can hold rq->nr_phys_segments entries
+ */
+int blk_rq_map_sg(struct request_queue *q, struct request *rq,
+		  struct scatterlist *sglist)
+{
+	struct bio_vec *bvec, *bvprv;
+	struct req_iterator iter;
+	struct scatterlist *sg;
+	int nsegs, cluster;
+
+	nsegs = 0;
+	cluster = q->queue_flags & (1 << QUEUE_FLAG_CLUSTER);
+
+	/*
+	 * for each bio in rq
+	 */
+	bvprv = NULL;
+	sg = NULL;
+	rq_for_each_segment(bvec, rq, iter) {
+		int nbytes = bvec->bv_len;
+
+		if (bvprv && cluster) {
+			if (sg->length + nbytes > q->max_segment_size)
+				goto new_segment;
+
+			if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec))
+				goto new_segment;
+			if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec))
+				goto new_segment;
+
+			sg->length += nbytes;
+		} else {
+new_segment:
+			if (!sg)
+				sg = sglist;
+			else {
+				/*
+				 * If the driver previously mapped a shorter
+				 * list, we could see a termination bit
+				 * prematurely unless it fully inits the sg
+				 * table on each mapping. We KNOW that there
+				 * must be more entries here or the driver
+				 * would be buggy, so force clear the
+				 * termination bit to avoid doing a full
+				 * sg_init_table() in drivers for each command.
+				 */
+				sg->page_link &= ~0x02;
+				sg = sg_next(sg);
+			}
+
+			sg_set_page(sg, bvec->bv_page, nbytes, bvec->bv_offset);
+			nsegs++;
+		}
+		bvprv = bvec;
+	} /* segments in rq */
+
+	if (q->dma_drain_size) {
+		sg->page_link &= ~0x02;
+		sg = sg_next(sg);
+		sg_set_page(sg, virt_to_page(q->dma_drain_buffer),
+			    q->dma_drain_size,
+			    ((unsigned long)q->dma_drain_buffer) &
+			    (PAGE_SIZE - 1));
+		nsegs++;
+	}
+
+	if (sg)
+		sg_mark_end(sg);
+
+	return nsegs;
+}
+
+EXPORT_SYMBOL(blk_rq_map_sg);
+
+static inline int ll_new_mergeable(struct request_queue *q,
+				   struct request *req,
+				   struct bio *bio)
+{
+	int nr_phys_segs = bio_phys_segments(q, bio);
+
+	if (req->nr_phys_segments + nr_phys_segs > q->max_phys_segments) {
+		req->cmd_flags |= REQ_NOMERGE;
+		if (req == q->last_merge)
+			q->last_merge = NULL;
+		return 0;
+	}
+
+	/*
+	 * A hw segment is just getting larger, bump just the phys
+	 * counter.
+	 */
+	req->nr_phys_segments += nr_phys_segs;
+	return 1;
+}
+
+static inline int ll_new_hw_segment(struct request_queue *q,
+				    struct request *req,
+				    struct bio *bio)
+{
+	int nr_hw_segs = bio_hw_segments(q, bio);
+	int nr_phys_segs = bio_phys_segments(q, bio);
+
+	if (req->nr_hw_segments + nr_hw_segs > q->max_hw_segments
+	    || req->nr_phys_segments + nr_phys_segs > q->max_phys_segments) {
+		req->cmd_flags |= REQ_NOMERGE;
+		if (req == q->last_merge)
+			q->last_merge = NULL;
+		return 0;
+	}
+
+	/*
+	 * This will form the start of a new hw segment.  Bump both
+	 * counters.
+	 */
+	req->nr_hw_segments += nr_hw_segs;
+	req->nr_phys_segments += nr_phys_segs;
+	return 1;
+}
+
+int ll_back_merge_fn(struct request_queue *q, struct request *req,
+		     struct bio *bio)
+{
+	unsigned short max_sectors;
+	int len;
+
+	if (unlikely(blk_pc_request(req)))
+		max_sectors = q->max_hw_sectors;
+	else
+		max_sectors = q->max_sectors;
+
+	if (req->nr_sectors + bio_sectors(bio) > max_sectors) {
+		req->cmd_flags |= REQ_NOMERGE;
+		if (req == q->last_merge)
+			q->last_merge = NULL;
+		return 0;
+	}
+	if (unlikely(!bio_flagged(req->biotail, BIO_SEG_VALID)))
+		blk_recount_segments(q, req->biotail);
+	if (unlikely(!bio_flagged(bio, BIO_SEG_VALID)))
+		blk_recount_segments(q, bio);
+	len = req->biotail->bi_hw_back_size + bio->bi_hw_front_size;
+	if (BIOVEC_VIRT_MERGEABLE(__BVEC_END(req->biotail), __BVEC_START(bio)) &&
+	    !BIOVEC_VIRT_OVERSIZE(len)) {
+		int mergeable =  ll_new_mergeable(q, req, bio);
+
+		if (mergeable) {
+			if (req->nr_hw_segments == 1)
+				req->bio->bi_hw_front_size = len;
+			if (bio->bi_hw_segments == 1)
+				bio->bi_hw_back_size = len;
+		}
+		return mergeable;
+	}
+
+	return ll_new_hw_segment(q, req, bio);
+}
+
+int ll_front_merge_fn(struct request_queue *q, struct request *req, 
+		      struct bio *bio)
+{
+	unsigned short max_sectors;
+	int len;
+
+	if (unlikely(blk_pc_request(req)))
+		max_sectors = q->max_hw_sectors;
+	else
+		max_sectors = q->max_sectors;
+
+
+	if (req->nr_sectors + bio_sectors(bio) > max_sectors) {
+		req->cmd_flags |= REQ_NOMERGE;
+		if (req == q->last_merge)
+			q->last_merge = NULL;
+		return 0;
+	}
+	len = bio->bi_hw_back_size + req->bio->bi_hw_front_size;
+	if (unlikely(!bio_flagged(bio, BIO_SEG_VALID)))
+		blk_recount_segments(q, bio);
+	if (unlikely(!bio_flagged(req->bio, BIO_SEG_VALID)))
+		blk_recount_segments(q, req->bio);
+	if (BIOVEC_VIRT_MERGEABLE(__BVEC_END(bio), __BVEC_START(req->bio)) &&
+	    !BIOVEC_VIRT_OVERSIZE(len)) {
+		int mergeable =  ll_new_mergeable(q, req, bio);
+
+		if (mergeable) {
+			if (bio->bi_hw_segments == 1)
+				bio->bi_hw_front_size = len;
+			if (req->nr_hw_segments == 1)
+				req->biotail->bi_hw_back_size = len;
+		}
+		return mergeable;
+	}
+
+	return ll_new_hw_segment(q, req, bio);
+}
+
+static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
+				struct request *next)
+{
+	int total_phys_segments;
+	int total_hw_segments;
+
+	/*
+	 * First check if the either of the requests are re-queued
+	 * requests.  Can't merge them if they are.
+	 */
+	if (req->special || next->special)
+		return 0;
+
+	/*
+	 * Will it become too large?
+	 */
+	if ((req->nr_sectors + next->nr_sectors) > q->max_sectors)
+		return 0;
+
+	total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
+	if (blk_phys_contig_segment(q, req->biotail, next->bio))
+		total_phys_segments--;
+
+	if (total_phys_segments > q->max_phys_segments)
+		return 0;
+
+	total_hw_segments = req->nr_hw_segments + next->nr_hw_segments;
+	if (blk_hw_contig_segment(q, req->biotail, next->bio)) {
+		int len = req->biotail->bi_hw_back_size + next->bio->bi_hw_front_size;
+		/*
+		 * propagate the combined length to the end of the requests
+		 */
+		if (req->nr_hw_segments == 1)
+			req->bio->bi_hw_front_size = len;
+		if (next->nr_hw_segments == 1)
+			next->biotail->bi_hw_back_size = len;
+		total_hw_segments--;
+	}
+
+	if (total_hw_segments > q->max_hw_segments)
+		return 0;
+
+	/* Merge is OK... */
+	req->nr_phys_segments = total_phys_segments;
+	req->nr_hw_segments = total_hw_segments;
+	return 1;
+}
+
+/*
+ * Has to be called with the request spinlock acquired
+ */
+static int attempt_merge(struct request_queue *q, struct request *req,
+			  struct request *next)
+{
+	if (!rq_mergeable(req) || !rq_mergeable(next))
+		return 0;
+
+	/*
+	 * not contiguous
+	 */
+	if (req->sector + req->nr_sectors != next->sector)
+		return 0;
+
+	if (rq_data_dir(req) != rq_data_dir(next)
+	    || req->rq_disk != next->rq_disk
+	    || next->special)
+		return 0;
+
+	/*
+	 * If we are allowed to merge, then append bio list
+	 * from next to rq and release next. merge_requests_fn
+	 * will have updated segment counts, update sector
+	 * counts here.
+	 */
+	if (!ll_merge_requests_fn(q, req, next))
+		return 0;
+
+	/*
+	 * At this point we have either done a back merge
+	 * or front merge. We need the smaller start_time of
+	 * the merged requests to be the current request
+	 * for accounting purposes.
+	 */
+	if (time_after(req->start_time, next->start_time))
+		req->start_time = next->start_time;
+
+	req->biotail->bi_next = next->bio;
+	req->biotail = next->biotail;
+
+	req->nr_sectors = req->hard_nr_sectors += next->hard_nr_sectors;
+
+	elv_merge_requests(q, req, next);
+
+	if (req->rq_disk) {
+		disk_round_stats(req->rq_disk);
+		req->rq_disk->in_flight--;
+	}
+
+	req->ioprio = ioprio_best(req->ioprio, next->ioprio);
+
+	__blk_put_request(q, next);
+	return 1;
+}
+
+int attempt_back_merge(struct request_queue *q, struct request *rq)
+{
+	struct request *next = elv_latter_request(q, rq);
+
+	if (next)
+		return attempt_merge(q, rq, next);
+
+	return 0;
+}
+
+int attempt_front_merge(struct request_queue *q, struct request *rq)
+{
+	struct request *prev = elv_former_request(q, rq);
+
+	if (prev)
+		return attempt_merge(q, prev, rq);
+
+	return 0;
+}
diff --git a/block/blk.h b/block/blk.h
index 0833940..ec898dd 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -14,8 +14,6 @@ void rq_init(struct request_queue *q, struct request *rq);
 void init_request_from_bio(struct request *req, struct bio *bio);
 void blk_rq_bio_prep(struct request_queue *q, struct request *rq,
 			struct bio *bio);
-int ll_back_merge_fn(struct request_queue *q, struct request *req,
-		     struct bio *bio);
 void __blk_queue_free_tags(struct request_queue *q);
 
 void blk_unplug_work(struct work_struct *work);
@@ -23,6 +21,15 @@ void blk_unplug_timeout(unsigned long data);
 
 struct io_context *current_io_context(gfp_t gfp_flags, int node);
 
+int ll_back_merge_fn(struct request_queue *q, struct request *req,
+		     struct bio *bio);
+int ll_front_merge_fn(struct request_queue *q, struct request *req, 
+		      struct bio *bio);
+int attempt_back_merge(struct request_queue *q, struct request *rq);
+int attempt_front_merge(struct request_queue *q, struct request *rq);
+void blk_recalc_rq_segments(struct request *rq);
+void blk_recalc_rq_sectors(struct request *rq, int nsect);
+
 void blk_queue_congestion_threshold(struct request_queue *q);
 
 /*