@@ -157,22 +157,36 @@ static unsigned get_max_segment_size(const struct request_queue *q,
queue_max_segment_size(q));
}
-/*
- * Split the bvec @bv into segments, and update all kinds of
- * variables.
+/**
+ * bvec_split_segs - verify whether or not a bvec should be split in the middle
+ * @q: [in] request queue associated with the bio associated with @bv
+ * @bv: [in] bvec to examine
+ * @nsegs: [in,out] Number of segments in the bio being built. Incremented
+ * by the number of segments from @bv that may be appended to that
+ * bio without exceeding @max_segs
+ * @sectors: [in,out] Number of sectors in the bio being built. Incremented
+ * by the number of sectors from @bv that may be appended to that
+ * bio without exceeding @max_sectors
+ * @max_segs: [in] upper bound for *@nsegs
+ * @max_sectors: [in] upper bound for *@sectors
+ *
+ * When splitting a bio, it can happen that a bvec is encountered that is too
+ * big to fit in a single segment and hence that it has to be split in the
+ * middle. This function verifies whether or not that should happen. The value
+ * %true is returned if and only if appending the entire @bv to a bio with
+ * *@nsegs segments and *@sectors sectors would make that bio unacceptable for
+ * the block driver.
*/
static bool bvec_split_segs(const struct request_queue *q,
const struct bio_vec *bv, unsigned *nsegs,
- unsigned *sectors, unsigned max_segs)
+ unsigned *sectors, unsigned max_segs,
+ unsigned max_sectors)
{
- unsigned len = bv->bv_len;
+ unsigned max_len = (min(max_sectors, UINT_MAX >> 9) - *sectors) << 9;
+ unsigned len = min(bv->bv_len, max_len);
unsigned total_len = 0;
unsigned seg_size = 0;
- /*
- * Multi-page bvec may be too big to hold in one segment, so the
- * current bvec has to be splitted as multiple segments.
- */
while (len && *nsegs < max_segs) {
seg_size = get_max_segment_size(q, bv->bv_offset + total_len);
seg_size = min(seg_size, len);
@@ -187,8 +201,8 @@ static bool bvec_split_segs(const struct request_queue *q,
*sectors += total_len >> 9;
- /* split in the middle of the bvec if len != 0 */
- return !!len;
+ /* tell the caller to split the bvec if it is too big to fit */
+ return len > 0 || bv->bv_len > max_len;
}
/**
@@ -229,34 +243,18 @@ static struct bio *blk_bio_segment_split(struct request_queue *q,
if (bvprvp && bvec_gap_to_prev(q, bvprvp, bv.bv_offset))
goto split;
- if (sectors + (bv.bv_len >> 9) > max_sectors) {
- /*
- * Consider this a new segment if we're splitting in
- * the middle of this vector.
- */
- if (nsegs < max_segs &&
- sectors < max_sectors) {
- /* split in the middle of bvec */
- bv.bv_len = (max_sectors - sectors) << 9;
- bvec_split_segs(q, &bv, &nsegs,
- §ors, max_segs);
- }
+ if (nsegs < max_segs &&
+ sectors + (bv.bv_len >> 9) <= max_sectors &&
+ bv.bv_offset + bv.bv_len <= PAGE_SIZE) {
+ nsegs++;
+ sectors += bv.bv_len >> 9;
+ } else if (bvec_split_segs(q, &bv, &nsegs, §ors, max_segs,
+ max_sectors)) {
goto split;
}
- if (nsegs == max_segs)
- goto split;
-
bvprv = bv;
bvprvp = &bvprv;
-
- if (bv.bv_offset + bv.bv_len <= PAGE_SIZE) {
- nsegs++;
- sectors += bv.bv_len >> 9;
- } else if (bvec_split_segs(q, &bv, &nsegs, §ors,
- max_segs)) {
- goto split;
- }
}
*segs = nsegs;
@@ -363,7 +361,7 @@ unsigned int blk_recalc_rq_segments(struct request *rq)
rq_for_each_bvec(bv, rq, iter)
bvec_split_segs(rq->q, &bv, &nr_phys_segs, &nr_sectors,
- UINT_MAX);
+ UINT_MAX, UINT_MAX);
return nr_phys_segs;
}
Move the max_sectors check into bvec_split_segs() such that a single call to that function can do all the necessary checks. This patch optimizes the fast path further, namely if a bvec fits in a page. Cc: Christoph Hellwig <hch@lst.de> Cc: Ming Lei <ming.lei@redhat.com> Cc: Hannes Reinecke <hare@suse.com> Signed-off-by: Bart Van Assche <bvanassche@acm.org> --- block/blk-merge.c | 68 +++++++++++++++++++++++------------------------ 1 file changed, 33 insertions(+), 35 deletions(-)