blk-merge.c

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/*
 * 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)->page_link &= ~0x02;
            *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;

    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);
    } /* 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);

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;
}

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;
}