first commit

1 files changed, 663 insertions, 0 deletions

diff --git a/block/blk-merge.c b/block/blk-merge.c
new file mode 100644
index 000000000..ef138cc03
--- /dev/null
+++ b/block/blk-merge.c
@@ -0,0 +1,663 @@
+/*
+ * 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"
+
+static unsigned int __blk_recalc_rq_segments(struct request_queue *q,
+					     struct bio *bio)
+{
+	struct bio_vec *bv, *bvprv = NULL;
+	int cluster, i, high, highprv = 1;
+	unsigned int seg_size, nr_phys_segs;
+	struct bio *fbio, *bbio;
+
+	if (!bio)
+		return 0;
+
+	fbio = bio;
+	cluster = blk_queue_cluster(q);
+	seg_size = 0;
+	nr_phys_segs = 0;
+	for_each_bio(bio) {
+		bio_for_each_segment(bv, bio, i) {
+			/*
+			 * 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) > queue_bounce_pfn(q);
+			if (high || highprv)
+				goto new_segment;
+			if (cluster) {
+				if (seg_size + bv->bv_len
+				    > queue_max_segment_size(q))
+					goto new_segment;
+				if (!BIOVEC_PHYS_MERGEABLE(bvprv, bv))
+					goto new_segment;
+				if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bv))
+					goto new_segment;
+
+				seg_size += bv->bv_len;
+				bvprv = bv;
+				continue;
+			}
+new_segment:
+			if (nr_phys_segs == 1 && seg_size >
+			    fbio->bi_seg_front_size)
+				fbio->bi_seg_front_size = seg_size;
+
+			nr_phys_segs++;
+			bvprv = bv;
+			seg_size = bv->bv_len;
+			highprv = high;
+		}
+		bbio = bio;
+	}
+
+	if (nr_phys_segs == 1 && seg_size > fbio->bi_seg_front_size)
+		fbio->bi_seg_front_size = seg_size;
+	if (seg_size > bbio->bi_seg_back_size)
+		bbio->bi_seg_back_size = seg_size;
+
+	return nr_phys_segs;
+}
+
+void blk_recalc_rq_segments(struct request *rq)
+{
+	rq->nr_phys_segments = __blk_recalc_rq_segments(rq->q, rq->bio);
+}
+
+void blk_recount_segments(struct request_queue *q, struct bio *bio)
+{
+	struct bio *nxt = bio->bi_next;
+
+	bio->bi_next = NULL;
+	bio->bi_phys_segments = __blk_recalc_rq_segments(q, bio);
+	bio->bi_next = nxt;
+	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 (!blk_queue_cluster(q))
+		return 0;
+
+	if (bio->bi_seg_back_size + nxt->bi_seg_front_size >
+	    queue_max_segment_size(q))
+		return 0;
+
+	if (!bio_has_data(bio))
+		return 1;
+
+	if (!BIOVEC_PHYS_MERGEABLE(__BVEC_END(bio), __BVEC_START(nxt)))
+		return 0;
+
+	/*
+	 * bio and nxt are contiguous 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 void
+__blk_segment_map_sg(struct request_queue *q, struct bio_vec *bvec,
+		     struct scatterlist *sglist, struct bio_vec **bvprv,
+		     struct scatterlist **sg, int *nsegs, int *cluster)
+{
+
+	int nbytes = bvec->bv_len;
+
+	if (*bvprv && *cluster) {
+		if ((*sg)->length + nbytes > queue_max_segment_size(q))
+			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_unmark_end(*sg);
+			*sg = sg_next(*sg);
+		}
+
+		sg_set_page(*sg, bvec->bv_page, nbytes, bvec->bv_offset);
+		(*nsegs)++;
+	}
+	*bvprv = bvec;
+}
+
+/*
+ * 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;
+#if defined(FEATURE_STORAGE_PID_LOGGER)
+        struct page_pid_logger *prev_logger = 0;
+#endif
+
+	nsegs = 0;
+	cluster = blk_queue_cluster(q);
+
+	/*
+	 * for each bio in rq
+	 */
+	bvprv = NULL;
+	sg = NULL;
+	rq_for_each_segment(bvec, rq, iter) {
+		__blk_segment_map_sg(q, bvec, sglist, &bvprv, &sg,
+				     &nsegs, &cluster);
+//#undef FEATURE_STORAGE_PID_LOGGER
+#if defined(FEATURE_STORAGE_PID_LOGGER)              
+			do {
+				extern spinlock_t g_locker;
+				extern unsigned char *page_logger;
+				
+				extern struct struct_pid_logger g_pid_logger[PID_ID_CNT];
+				unsigned long flags;
+				if(page_logger) { 
+					struct page_pid_logger *tmp_logger;
+					unsigned long page_offset;
+					int index, mmcqd_index;
+					pid_t current_pid=0;
+					//#if defined(CONFIG_FLATMEM)
+					//page_offset = (unsigned long)((bvec->bv_page) - mem_map);
+					//#else
+					page_offset = (unsigned long)(__page_to_pfn(bvec->bv_page))- PHYS_PFN_OFFSET;
+					//#endif
+					tmp_logger =((struct page_pid_logger *)page_logger) + page_offset;
+					//tmp_locker =((struct page_pid_locker *)page_logger_lock) + page_offset;
+					#if defined(CONFIG_FLATMEM)
+					//printk(KERN_INFO"hank merge pid1:%u pid2:%u bv_page:%p vmemmap:%p pfn:%ld %s \n", tmp_logger->pid1, tmp_logger->pid2, bvec->bv_page, vmemmap, (unsigned long)(__page_to_pfn(bvec->bv_page)), q->backing_dev_info.name);
+					#else
+					//printk(KERN_INFO"hank merge pid1:%u pid2:%u bv_page:%x mem_map:%x pfn:%d %s \n", tmp_logger->pid1, tmp_logger->pid2, bvec->bv_page, mem_map, (unsigned long)(__page_to_pfn(bvec->bv_page)), q->backing_dev_info.name);
+					#endif
+					current_pid = current->pid;
+
+					//find the exactly pid record array
+					for( mmcqd_index=0; mmcqd_index<PID_ID_CNT; mmcqd_index++) {
+						//printk(KERN_INFO"hank merge mmcqd_index:%d qcurrent_pid:%d current_pid:%d", mmcqd_index, g_pid_logger[mmcqd_index].current_pid, current_pid);
+						if( g_pid_logger[mmcqd_index].current_pid==0 || g_pid_logger[mmcqd_index].current_pid == current_pid ) {
+							g_pid_logger[mmcqd_index].current_pid = current_pid;
+							break;
+						}		
+					}
+					//no match array
+					if( mmcqd_index == PID_ID_CNT )
+						break;
+					/*
+					if( tmp_logger->pid1 == 0XFFFF && tmp_logger->pid2 == 0XFFFF)
+                                        {
+                                           printk(KERN_INFO"hank merge fail offset:%d of:%d bytes:%d rw:%d", page_offset, bvec->bv_offset, nbytes, (rq->cmd_flags & REQ_WRITE));
+                                        }else
+                                        {
+                                           printk(KERN_INFO"hank merge success offset:%d of:%d bytes:%d rw:%d", page_offset, bvec->bv_offset, nbytes, (rq->cmd_flags & REQ_WRITE));
+                                        }
+					*/
+					if( tmp_logger->pid1 != 0xFFFF) {
+						spin_lock_irqsave(&g_locker, flags);
+						for( index=0; index<PID_LOGGER_COUNT; index++) {
+							if( tmp_logger->pid1 == 0xFFFF)
+								break;
+							if( (g_pid_logger[mmcqd_index].pid_logger[index] == 0 || g_pid_logger[mmcqd_index].pid_logger[index] == tmp_logger->pid1)) {
+								g_pid_logger[mmcqd_index].pid_logger[index] = tmp_logger->pid1;
+								if (rq->cmd_flags & REQ_WRITE) {
+									g_pid_logger[mmcqd_index].pid_logger_counter[index]++;
+									g_pid_logger[mmcqd_index].pid_logger_length[index]+=bvec->bv_len;
+								}else {
+									g_pid_logger[mmcqd_index].pid_logger_r_counter[index]++;
+									g_pid_logger[mmcqd_index].pid_logger_r_length[index]+=bvec->bv_len;
+								}
+								if( prev_logger && prev_logger != tmp_logger)
+								   prev_logger->pid1 = 0XFFFF;
+								//tmp_logger->pid1 = 0XFFFF;
+								break;
+							}
+							
+							
+						}
+#if defined(CONFIG_MTK_MORE_PID_LOGGER_COUNT)						
+						if(index==PID_LOGGER_COUNT && g_pid_logger[mmcqd_index].reserved<10){
+							 	if (rq->cmd_flags & REQ_WRITE) {
+									printk(KERN_INFO"[BLOCK_TAG]exceed logger count,pid%d w length %d",tmp_logger->pid1,bvec->bv_len);
+								}else {
+									printk(KERN_INFO"[BLOCK_TAG]exceed logger count,pid%d r length %d",tmp_logger->pid1,bvec->bv_len);
+								}
+								g_pid_logger[mmcqd_index].reserved++;
+						}
+#endif						
+						spin_unlock_irqrestore(&g_locker, flags);
+					}
+					if( tmp_logger->pid2 != 0xFFFF) {
+						spin_lock_irqsave(&g_locker, flags);
+						for( index=0; index<PID_LOGGER_COUNT; index++) {
+							if( tmp_logger->pid2 == 0xFFFF)
+								break;
+							if( (g_pid_logger[mmcqd_index].pid_logger[index] == 0 || g_pid_logger[mmcqd_index].pid_logger[index] == tmp_logger->pid2)) {
+								g_pid_logger[mmcqd_index].pid_logger[index] = tmp_logger->pid2;
+								if (rq->cmd_flags & REQ_WRITE) {
+									g_pid_logger[mmcqd_index].pid_logger_counter[index]++;
+									g_pid_logger[mmcqd_index].pid_logger_length[index]+=bvec->bv_len;
+								}else {
+									g_pid_logger[mmcqd_index].pid_logger_r_counter[index]++;
+									g_pid_logger[mmcqd_index].pid_logger_r_length[index]+=bvec->bv_len;
+								}
+								if( prev_logger && prev_logger != tmp_logger)
+								   prev_logger->pid2 = 0XFFFF;
+								//tmp_logger->pid2 = 0XFFFF;
+								break;
+							}
+							
+						}
+#if defined(CONFIG_MTK_MORE_PID_LOGGER_COUNT)						
+                         if(index==PID_LOGGER_COUNT && g_pid_logger[mmcqd_index].reserved<10){
+							 	if (rq->cmd_flags & REQ_WRITE) {
+									printk(KERN_INFO"[BLOCK_TAG]exceed logger count,pid%d w length %d",tmp_logger->pid2,bvec->bv_len);
+								}else {
+									printk(KERN_INFO"[BLOCK_TAG]exceed logger count,pid%d r length %d",tmp_logger->pid2,bvec->bv_len);
+								}
+								g_pid_logger[mmcqd_index].reserved++;
+							}
+#endif						 
+						spin_unlock_irqrestore(&g_locker, flags);
+					}
+					prev_logger = tmp_logger;
+					
+				}
+			} while (0);
+						
+#endif
+	} /* segments in rq */
+
+
+	if (unlikely(rq->cmd_flags & REQ_COPY_USER) &&
+	    (blk_rq_bytes(rq) & q->dma_pad_mask)) {
+		unsigned int pad_len =
+			(q->dma_pad_mask & ~blk_rq_bytes(rq)) + 1;
+
+		sg->length += pad_len;
+		rq->extra_len += pad_len;
+	}
+
+	if (q->dma_drain_size && q->dma_drain_needed(rq)) {
+		if (rq->cmd_flags & REQ_WRITE)
+			memset(q->dma_drain_buffer, 0, 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++;
+		rq->extra_len += q->dma_drain_size;
+	}
+
+	if (sg)
+		sg_mark_end(sg);
+
+	return nsegs;
+}
+EXPORT_SYMBOL(blk_rq_map_sg);
+
+/**
+ * blk_bio_map_sg - map a bio to a scatterlist
+ * @q: request_queue in question
+ * @bio: bio being mapped
+ * @sglist: scatterlist being mapped
+ *
+ * Note:
+ *    Caller must make sure sg can hold bio->bi_phys_segments entries
+ *
+ * Will return the number of sg entries setup
+ */
+int blk_bio_map_sg(struct request_queue *q, struct bio *bio,
+		   struct scatterlist *sglist)
+{
+	struct bio_vec *bvec, *bvprv;
+	struct scatterlist *sg;
+	int nsegs, cluster;
+	unsigned long i;
+
+	nsegs = 0;
+	cluster = blk_queue_cluster(q);
+
+	bvprv = NULL;
+	sg = NULL;
+	bio_for_each_segment(bvec, bio, i) {
+		__blk_segment_map_sg(q, bvec, sglist, &bvprv, &sg,
+				     &nsegs, &cluster);
+	} /* segments in bio */
+
+	if (sg)
+		sg_mark_end(sg);
+
+	BUG_ON(bio->bi_phys_segments && nsegs > bio->bi_phys_segments);
+	return nsegs;
+}
+EXPORT_SYMBOL(blk_bio_map_sg);
+
+static inline int ll_new_hw_segment(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 > queue_max_segments(q))
+		goto no_merge;
+
+	if (bio_integrity(bio) && blk_integrity_merge_bio(q, req, bio))
+		goto no_merge;
+
+	/*
+	 * This will form the start of a new hw segment.  Bump both
+	 * counters.
+	 */
+	req->nr_phys_segments += nr_phys_segs;
+	return 1;
+
+no_merge:
+	req->cmd_flags |= REQ_NOMERGE;
+	if (req == q->last_merge)
+		q->last_merge = NULL;
+	return 0;
+}
+
+int ll_back_merge_fn(struct request_queue *q, struct request *req,
+		     struct bio *bio)
+{
+	if (blk_rq_sectors(req) + bio_sectors(bio) >
+	    blk_rq_get_max_sectors(req)) {
+		req->cmd_flags |= REQ_NOMERGE;
+		if (req == q->last_merge)
+			q->last_merge = NULL;
+		return 0;
+	}
+	if (!bio_flagged(req->biotail, BIO_SEG_VALID))
+		blk_recount_segments(q, req->biotail);
+	if (!bio_flagged(bio, BIO_SEG_VALID))
+		blk_recount_segments(q, bio);
+
+	return ll_new_hw_segment(q, req, bio);
+}
+
+int ll_front_merge_fn(struct request_queue *q, struct request *req,
+		      struct bio *bio)
+{
+	if (blk_rq_sectors(req) + bio_sectors(bio) >
+	    blk_rq_get_max_sectors(req)) {
+		req->cmd_flags |= REQ_NOMERGE;
+		if (req == q->last_merge)
+			q->last_merge = NULL;
+		return 0;
+	}
+	if (!bio_flagged(bio, BIO_SEG_VALID))
+		blk_recount_segments(q, bio);
+	if (!bio_flagged(req->bio, BIO_SEG_VALID))
+		blk_recount_segments(q, req->bio);
+
+	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;
+	unsigned int seg_size =
+		req->biotail->bi_seg_back_size + next->bio->bi_seg_front_size;
+
+	/*
+	 * 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 ((blk_rq_sectors(req) + blk_rq_sectors(next)) >
+	    blk_rq_get_max_sectors(req))
+		return 0;
+
+	total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
+	if (blk_phys_contig_segment(q, req->biotail, next->bio)) {
+		if (req->nr_phys_segments == 1)
+			req->bio->bi_seg_front_size = seg_size;
+		if (next->nr_phys_segments == 1)
+			next->biotail->bi_seg_back_size = seg_size;
+		total_phys_segments--;
+	}
+
+	if (total_phys_segments > queue_max_segments(q))
+		return 0;
+
+	if (blk_integrity_rq(req) && blk_integrity_merge_rq(q, req, next))
+		return 0;
+
+	/* Merge is OK... */
+	req->nr_phys_segments = total_phys_segments;
+	return 1;
+}
+
+/**
+ * blk_rq_set_mixed_merge - mark a request as mixed merge
+ * @rq: request to mark as mixed merge
+ *
+ * Description:
+ *     @rq is about to be mixed merged.  Make sure the attributes
+ *     which can be mixed are set in each bio and mark @rq as mixed
+ *     merged.
+ */
+void blk_rq_set_mixed_merge(struct request *rq)
+{
+	unsigned int ff = rq->cmd_flags & REQ_FAILFAST_MASK;
+	struct bio *bio;
+
+	if (rq->cmd_flags & REQ_MIXED_MERGE)
+		return;
+
+	/*
+	 * @rq will no longer represent mixable attributes for all the
+	 * contained bios.  It will just track those of the first one.
+	 * Distributes the attributs to each bio.
+	 */
+	for (bio = rq->bio; bio; bio = bio->bi_next) {
+		WARN_ON_ONCE((bio->bi_rw & REQ_FAILFAST_MASK) &&
+			     (bio->bi_rw & REQ_FAILFAST_MASK) != ff);
+		bio->bi_rw |= ff;
+	}
+	rq->cmd_flags |= REQ_MIXED_MERGE;
+}
+
+static void blk_account_io_merge(struct request *req)
+{
+	if (blk_do_io_stat(req)) {
+		struct hd_struct *part;
+		int cpu;
+
+		cpu = part_stat_lock();
+		part = req->part;
+
+		part_round_stats(cpu, part);
+		part_dec_in_flight(part, rq_data_dir(req));
+
+		hd_struct_put(part);
+		part_stat_unlock();
+	}
+}
+
+/*
+ * 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;
+
+	if (!blk_check_merge_flags(req->cmd_flags, next->cmd_flags))
+		return 0;
+
+	/*
+	 * not contiguous
+	 */
+	if (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next))
+		return 0;
+
+	if (rq_data_dir(req) != rq_data_dir(next)
+	    || req->rq_disk != next->rq_disk
+	    || next->special)
+		return 0;
+
+	if (req->cmd_flags & REQ_WRITE_SAME &&
+	    !blk_write_same_mergeable(req->bio, next->bio))
+		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;
+
+	/*
+	 * If failfast settings disagree or any of the two is already
+	 * a mixed merge, mark both as mixed before proceeding.  This
+	 * makes sure that all involved bios have mixable attributes
+	 * set properly.
+	 */
+	if ((req->cmd_flags | next->cmd_flags) & REQ_MIXED_MERGE ||
+	    (req->cmd_flags & REQ_FAILFAST_MASK) !=
+	    (next->cmd_flags & REQ_FAILFAST_MASK)) {
+		blk_rq_set_mixed_merge(req);
+		blk_rq_set_mixed_merge(next);
+	}
+
+	/*
+	 * 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->__data_len += blk_rq_bytes(next);
+
+	elv_merge_requests(q, req, next);
+
+	/*
+	 * 'next' is going away, so update stats accordingly
+	 */
+	blk_account_io_merge(next);
+
+	req->ioprio = ioprio_best(req->ioprio, next->ioprio);
+	if (blk_rq_cpu_valid(next))
+		req->cpu = next->cpu;
+
+	/* owner-ship of bio passed from next to req */
+	next->bio = NULL;
+	__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;
+}
+
+int blk_attempt_req_merge(struct request_queue *q, struct request *rq,
+			  struct request *next)
+{
+	return attempt_merge(q, rq, next);
+}
+
+bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
+{
+	if (!rq_mergeable(rq) || !bio_mergeable(bio))
+		return false;
+
+	if (!blk_check_merge_flags(rq->cmd_flags, bio->bi_rw))
+		return false;
+
+	/* different data direction or already started, don't merge */
+	if (bio_data_dir(bio) != rq_data_dir(rq))
+		return false;
+
+	/* must be same device and not a special request */
+	if (rq->rq_disk != bio->bi_bdev->bd_disk || rq->special)
+		return false;
+
+	/* only merge integrity protected bio into ditto rq */
+	if (bio_integrity(bio) != blk_integrity_rq(rq))
+		return false;
+
+	/* must be using the same buffer */
+	if (rq->cmd_flags & REQ_WRITE_SAME &&
+	    !blk_write_same_mergeable(rq->bio, bio))
+		return false;
+
+	return true;
+}
+
+int blk_try_merge(struct request *rq, struct bio *bio)
+{
+	if (blk_rq_pos(rq) + blk_rq_sectors(rq) == bio->bi_sector)
+		return ELEVATOR_BACK_MERGE;
+	else if (blk_rq_pos(rq) - bio_sectors(bio) == bio->bi_sector)
+		return ELEVATOR_FRONT_MERGE;
+	return ELEVATOR_NO_MERGE;
+}