@@ -132,16 +132,29 @@ static struct bio *blk_bio_write_same_split(struct request_queue *q,
return bio_split(bio, q->limits.max_write_same_sectors, GFP_NOIO, bs);
}
+/*
+ * Return the maximum number of sectors from the start of a bio that may be
+ * submitted as a single request to a block device. If enough sectors remain,
+ * align the end to the physical block size. Otherwise align the end to the
+ * logical block size. This approach minimizes the number of non-aligned
+ * requests that are submitted to a block device if the start of a bio is not
+ * aligned to a physical block boundary.
+ */
static inline unsigned get_max_io_size(struct request_queue *q,
struct bio *bio)
{
unsigned sectors = blk_max_size_offset(q, bio->bi_iter.bi_sector);
- unsigned mask = queue_logical_block_size(q) - 1;
+ unsigned max_sectors = sectors;
+ unsigned pbs = queue_physical_block_size(q) >> SECTOR_SHIFT;
+ unsigned lbs = queue_logical_block_size(q) >> SECTOR_SHIFT;
+ unsigned start_offset = bio->bi_iter.bi_sector & (pbs - 1);
- /* aligned to logical block size */
- sectors &= ~(mask >> 9);
+ max_sectors += start_offset;
+ max_sectors &= ~(pbs - 1);
+ if (max_sectors > start_offset)
+ return max_sectors - start_offset;
- return sectors;
+ return sectors & (lbs - 1);
}
static unsigned get_max_segment_size(const struct request_queue *q,
Consider the following example: * The logical block size is 4 KB. * The physical block size is 8 KB. * max_sectors equals (16 KB >> 9) sectors. * A non-aligned 4 KB and an aligned 64 KB bio are merged into a single non-aligned 68 KB bio. The current behavior is to split such a bio into (16 KB + 16 KB + 16 KB + 16 KB + 4 KB). The start of none of these five bio's is aligned to a physical block boundary. This patch ensures that such a bio is split into four aligned and one non-aligned bio instead of being split into five non-aligned bios. This improves performance because most block devices can handle aligned requests faster than non-aligned requests. Since the physical block size is larger than or equal to the logical block size, this patch preserves the guarantee that the returned value is a multiple of the logical block size. Cc: Christoph Hellwig <hch@infradead.org> 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 | 21 +++++++++++++++++---- 1 file changed, 17 insertions(+), 4 deletions(-)