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https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
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![Jens Axboe](/assets/img/avatar_default.png)
One of the disadvantages of on-stack plugging is that we potentially lose out on merging since all pending IO isn't always visible to everybody. When we flush the on-stack plugs, right now we don't do any checks to see if potential merge candidates could be utilized. Correct this by adding a new insert variant, ELEVATOR_INSERT_SORT_MERGE. It works just ELEVATOR_INSERT_SORT, but first checks whether we can merge with an existing request before doing the insertion (if we fail merging). This fixes a regression with multiple processes issuing IO that can be merged. Thanks to Shaohua Li <shaohua.li@intel.com> for testing and fixing an accounting bug. Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
473 lines
11 KiB
C
473 lines
11 KiB
C
/*
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* Functions related to segment and merge handling
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*/
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/bio.h>
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#include <linux/blkdev.h>
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#include <linux/scatterlist.h>
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#include "blk.h"
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static unsigned int __blk_recalc_rq_segments(struct request_queue *q,
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struct bio *bio)
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{
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struct bio_vec *bv, *bvprv = NULL;
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int cluster, i, high, highprv = 1;
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unsigned int seg_size, nr_phys_segs;
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struct bio *fbio, *bbio;
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if (!bio)
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return 0;
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fbio = bio;
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cluster = blk_queue_cluster(q);
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seg_size = 0;
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nr_phys_segs = 0;
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for_each_bio(bio) {
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bio_for_each_segment(bv, bio, i) {
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/*
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* the trick here is making sure that a high page is
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* never considered part of another segment, since that
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* might change with the bounce page.
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*/
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high = page_to_pfn(bv->bv_page) > queue_bounce_pfn(q);
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if (high || highprv)
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goto new_segment;
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if (cluster) {
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if (seg_size + bv->bv_len
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> queue_max_segment_size(q))
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goto new_segment;
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if (!BIOVEC_PHYS_MERGEABLE(bvprv, bv))
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goto new_segment;
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if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bv))
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goto new_segment;
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seg_size += bv->bv_len;
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bvprv = bv;
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continue;
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}
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new_segment:
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if (nr_phys_segs == 1 && seg_size >
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fbio->bi_seg_front_size)
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fbio->bi_seg_front_size = seg_size;
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nr_phys_segs++;
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bvprv = bv;
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seg_size = bv->bv_len;
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highprv = high;
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}
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bbio = bio;
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}
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if (nr_phys_segs == 1 && seg_size > fbio->bi_seg_front_size)
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fbio->bi_seg_front_size = seg_size;
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if (seg_size > bbio->bi_seg_back_size)
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bbio->bi_seg_back_size = seg_size;
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return nr_phys_segs;
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}
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void blk_recalc_rq_segments(struct request *rq)
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{
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rq->nr_phys_segments = __blk_recalc_rq_segments(rq->q, rq->bio);
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}
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void blk_recount_segments(struct request_queue *q, struct bio *bio)
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{
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struct bio *nxt = bio->bi_next;
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bio->bi_next = NULL;
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bio->bi_phys_segments = __blk_recalc_rq_segments(q, bio);
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bio->bi_next = nxt;
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bio->bi_flags |= (1 << BIO_SEG_VALID);
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}
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EXPORT_SYMBOL(blk_recount_segments);
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static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio,
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struct bio *nxt)
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{
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if (!blk_queue_cluster(q))
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return 0;
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if (bio->bi_seg_back_size + nxt->bi_seg_front_size >
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queue_max_segment_size(q))
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return 0;
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if (!bio_has_data(bio))
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return 1;
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if (!BIOVEC_PHYS_MERGEABLE(__BVEC_END(bio), __BVEC_START(nxt)))
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return 0;
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/*
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* bio and nxt are contiguous in memory; check if the queue allows
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* these two to be merged into one
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*/
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if (BIO_SEG_BOUNDARY(q, bio, nxt))
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return 1;
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return 0;
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}
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/*
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* map a request to scatterlist, return number of sg entries setup. Caller
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* must make sure sg can hold rq->nr_phys_segments entries
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*/
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int blk_rq_map_sg(struct request_queue *q, struct request *rq,
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struct scatterlist *sglist)
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{
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struct bio_vec *bvec, *bvprv;
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struct req_iterator iter;
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struct scatterlist *sg;
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int nsegs, cluster;
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nsegs = 0;
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cluster = blk_queue_cluster(q);
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/*
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* for each bio in rq
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*/
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bvprv = NULL;
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sg = NULL;
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rq_for_each_segment(bvec, rq, iter) {
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int nbytes = bvec->bv_len;
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if (bvprv && cluster) {
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if (sg->length + nbytes > queue_max_segment_size(q))
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goto new_segment;
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if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec))
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goto new_segment;
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if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec))
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goto new_segment;
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sg->length += nbytes;
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} else {
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new_segment:
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if (!sg)
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sg = sglist;
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else {
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/*
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* If the driver previously mapped a shorter
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* list, we could see a termination bit
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* prematurely unless it fully inits the sg
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* table on each mapping. We KNOW that there
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* must be more entries here or the driver
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* would be buggy, so force clear the
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* termination bit to avoid doing a full
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* sg_init_table() in drivers for each command.
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*/
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sg->page_link &= ~0x02;
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sg = sg_next(sg);
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}
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sg_set_page(sg, bvec->bv_page, nbytes, bvec->bv_offset);
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nsegs++;
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}
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bvprv = bvec;
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} /* segments in rq */
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if (unlikely(rq->cmd_flags & REQ_COPY_USER) &&
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(blk_rq_bytes(rq) & q->dma_pad_mask)) {
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unsigned int pad_len =
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(q->dma_pad_mask & ~blk_rq_bytes(rq)) + 1;
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sg->length += pad_len;
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rq->extra_len += pad_len;
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}
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if (q->dma_drain_size && q->dma_drain_needed(rq)) {
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if (rq->cmd_flags & REQ_WRITE)
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memset(q->dma_drain_buffer, 0, q->dma_drain_size);
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sg->page_link &= ~0x02;
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sg = sg_next(sg);
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sg_set_page(sg, virt_to_page(q->dma_drain_buffer),
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q->dma_drain_size,
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((unsigned long)q->dma_drain_buffer) &
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(PAGE_SIZE - 1));
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nsegs++;
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rq->extra_len += q->dma_drain_size;
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}
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if (sg)
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sg_mark_end(sg);
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return nsegs;
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}
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EXPORT_SYMBOL(blk_rq_map_sg);
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static inline int ll_new_hw_segment(struct request_queue *q,
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struct request *req,
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struct bio *bio)
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{
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int nr_phys_segs = bio_phys_segments(q, bio);
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if (req->nr_phys_segments + nr_phys_segs > queue_max_segments(q))
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goto no_merge;
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if (bio_integrity(bio) && blk_integrity_merge_bio(q, req, bio))
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goto no_merge;
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/*
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* This will form the start of a new hw segment. Bump both
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* counters.
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*/
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req->nr_phys_segments += nr_phys_segs;
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return 1;
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no_merge:
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req->cmd_flags |= REQ_NOMERGE;
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if (req == q->last_merge)
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q->last_merge = NULL;
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return 0;
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}
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int ll_back_merge_fn(struct request_queue *q, struct request *req,
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struct bio *bio)
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{
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unsigned short max_sectors;
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if (unlikely(req->cmd_type == REQ_TYPE_BLOCK_PC))
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max_sectors = queue_max_hw_sectors(q);
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else
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max_sectors = queue_max_sectors(q);
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if (blk_rq_sectors(req) + bio_sectors(bio) > max_sectors) {
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req->cmd_flags |= REQ_NOMERGE;
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if (req == q->last_merge)
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q->last_merge = NULL;
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return 0;
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}
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if (!bio_flagged(req->biotail, BIO_SEG_VALID))
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blk_recount_segments(q, req->biotail);
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if (!bio_flagged(bio, BIO_SEG_VALID))
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blk_recount_segments(q, bio);
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return ll_new_hw_segment(q, req, bio);
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}
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int ll_front_merge_fn(struct request_queue *q, struct request *req,
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struct bio *bio)
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{
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unsigned short max_sectors;
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if (unlikely(req->cmd_type == REQ_TYPE_BLOCK_PC))
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max_sectors = queue_max_hw_sectors(q);
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else
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max_sectors = queue_max_sectors(q);
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if (blk_rq_sectors(req) + bio_sectors(bio) > max_sectors) {
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req->cmd_flags |= REQ_NOMERGE;
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if (req == q->last_merge)
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q->last_merge = NULL;
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return 0;
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}
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if (!bio_flagged(bio, BIO_SEG_VALID))
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blk_recount_segments(q, bio);
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if (!bio_flagged(req->bio, BIO_SEG_VALID))
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blk_recount_segments(q, req->bio);
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return ll_new_hw_segment(q, req, bio);
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}
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static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
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struct request *next)
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{
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int total_phys_segments;
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unsigned int seg_size =
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req->biotail->bi_seg_back_size + next->bio->bi_seg_front_size;
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/*
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* First check if the either of the requests are re-queued
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* requests. Can't merge them if they are.
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*/
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if (req->special || next->special)
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return 0;
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/*
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* Will it become too large?
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*/
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if ((blk_rq_sectors(req) + blk_rq_sectors(next)) > queue_max_sectors(q))
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return 0;
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total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
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if (blk_phys_contig_segment(q, req->biotail, next->bio)) {
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if (req->nr_phys_segments == 1)
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req->bio->bi_seg_front_size = seg_size;
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if (next->nr_phys_segments == 1)
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next->biotail->bi_seg_back_size = seg_size;
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total_phys_segments--;
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}
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if (total_phys_segments > queue_max_segments(q))
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return 0;
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if (blk_integrity_rq(req) && blk_integrity_merge_rq(q, req, next))
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return 0;
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/* Merge is OK... */
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req->nr_phys_segments = total_phys_segments;
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return 1;
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}
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/**
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* blk_rq_set_mixed_merge - mark a request as mixed merge
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* @rq: request to mark as mixed merge
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*
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* Description:
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* @rq is about to be mixed merged. Make sure the attributes
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* which can be mixed are set in each bio and mark @rq as mixed
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* merged.
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*/
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void blk_rq_set_mixed_merge(struct request *rq)
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{
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unsigned int ff = rq->cmd_flags & REQ_FAILFAST_MASK;
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struct bio *bio;
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if (rq->cmd_flags & REQ_MIXED_MERGE)
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return;
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/*
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* @rq will no longer represent mixable attributes for all the
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* contained bios. It will just track those of the first one.
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* Distributes the attributs to each bio.
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*/
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for (bio = rq->bio; bio; bio = bio->bi_next) {
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WARN_ON_ONCE((bio->bi_rw & REQ_FAILFAST_MASK) &&
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(bio->bi_rw & REQ_FAILFAST_MASK) != ff);
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bio->bi_rw |= ff;
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}
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rq->cmd_flags |= REQ_MIXED_MERGE;
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}
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static void blk_account_io_merge(struct request *req)
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{
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if (blk_do_io_stat(req)) {
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struct hd_struct *part;
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int cpu;
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cpu = part_stat_lock();
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part = req->part;
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part_round_stats(cpu, part);
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part_dec_in_flight(part, rq_data_dir(req));
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hd_struct_put(part);
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part_stat_unlock();
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}
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}
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/*
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* Has to be called with the request spinlock acquired
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*/
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static int attempt_merge(struct request_queue *q, struct request *req,
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struct request *next)
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{
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if (!rq_mergeable(req) || !rq_mergeable(next))
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return 0;
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/*
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* Don't merge file system requests and discard requests
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*/
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if ((req->cmd_flags & REQ_DISCARD) != (next->cmd_flags & REQ_DISCARD))
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return 0;
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/*
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* Don't merge discard requests and secure discard requests
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*/
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if ((req->cmd_flags & REQ_SECURE) != (next->cmd_flags & REQ_SECURE))
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return 0;
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/*
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* not contiguous
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*/
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if (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next))
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return 0;
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if (rq_data_dir(req) != rq_data_dir(next)
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|| req->rq_disk != next->rq_disk
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|| next->special)
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return 0;
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/*
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* If we are allowed to merge, then append bio list
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* from next to rq and release next. merge_requests_fn
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* will have updated segment counts, update sector
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* counts here.
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*/
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if (!ll_merge_requests_fn(q, req, next))
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return 0;
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/*
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* If failfast settings disagree or any of the two is already
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* a mixed merge, mark both as mixed before proceeding. This
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* makes sure that all involved bios have mixable attributes
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* set properly.
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*/
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if ((req->cmd_flags | next->cmd_flags) & REQ_MIXED_MERGE ||
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(req->cmd_flags & REQ_FAILFAST_MASK) !=
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(next->cmd_flags & REQ_FAILFAST_MASK)) {
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blk_rq_set_mixed_merge(req);
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blk_rq_set_mixed_merge(next);
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}
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/*
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* At this point we have either done a back merge
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* or front merge. We need the smaller start_time of
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* the merged requests to be the current request
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* for accounting purposes.
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*/
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if (time_after(req->start_time, next->start_time))
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req->start_time = next->start_time;
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req->biotail->bi_next = next->bio;
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req->biotail = next->biotail;
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req->__data_len += blk_rq_bytes(next);
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elv_merge_requests(q, req, next);
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/*
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* 'next' is going away, so update stats accordingly
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*/
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blk_account_io_merge(next);
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req->ioprio = ioprio_best(req->ioprio, next->ioprio);
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if (blk_rq_cpu_valid(next))
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req->cpu = next->cpu;
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/* owner-ship of bio passed from next to req */
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next->bio = NULL;
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__blk_put_request(q, next);
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return 1;
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}
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int attempt_back_merge(struct request_queue *q, struct request *rq)
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{
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struct request *next = elv_latter_request(q, rq);
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if (next)
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return attempt_merge(q, rq, next);
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return 0;
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}
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int attempt_front_merge(struct request_queue *q, struct request *rq)
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{
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struct request *prev = elv_former_request(q, rq);
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if (prev)
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return attempt_merge(q, prev, rq);
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return 0;
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}
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int blk_attempt_req_merge(struct request_queue *q, struct request *rq,
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struct request *next)
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{
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return attempt_merge(q, rq, next);
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}
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