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 2002046d0a9e..5a43c7d79594 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 99f4d641edf5..8ff99440ee44 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 000000000000..5023f0b08073
--- /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 083394007199..ec898dd0c65c 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);
 
 /*