/* * 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) { unsigned int phys_size; 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 = test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags); seg_size = 0; phys_size = 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 (!test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags)) 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; } /* * 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 = test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags); /* * 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 > 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->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 (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_RW) 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); 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_hw_segments(q) || req->nr_phys_segments + nr_phys_segs > queue_max_phys_segments(q)) { 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_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; if (unlikely(blk_pc_request(req))) max_sectors = queue_max_hw_sectors(q); else max_sectors = queue_max_sectors(q); if (blk_rq_sectors(req) + bio_sectors(bio) > max_sectors) { 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) { unsigned short max_sectors; if (unlikely(blk_pc_request(req))) max_sectors = queue_max_hw_sectors(q); else max_sectors = queue_max_sectors(q); if (blk_rq_sectors(req) + bio_sectors(bio) > max_sectors) { 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)) > queue_max_sectors(q)) 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_phys_segments(q)) return 0; if (total_phys_segments > queue_max_hw_segments(q)) return 0; /* Merge is OK... */ req->nr_phys_segments = total_phys_segments; return 1; } 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 = disk_map_sector_rcu(req->rq_disk, blk_rq_pos(req)); part_round_stats(cpu, part); part_dec_in_flight(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; /* * 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 (blk_integrity_rq(req) != blk_integrity_rq(next)) 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->__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; }