block: add notion of a chunk size for request merging
Some drivers have different limits on what size a request should
optimally be, depending on the offset of the request. Similar to
dividing a device into chunks. Add a setting that allows the driver
to inform the block layer of such a chunk size. The block layer will
then prevent merging across the chunks.
This is needed to optimally support NVMe with a non-zero stripe size.
Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/block/bio.c b/block/bio.c
index 96d28ee..97e832c 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -849,7 +849,8 @@
unsigned int offset)
{
struct request_queue *q = bdev_get_queue(bio->bi_bdev);
- return __bio_add_page(q, bio, page, len, offset, queue_max_sectors(q));
+
+ return __bio_add_page(q, bio, page, len, offset, blk_max_size_offset(q, bio->bi_iter.bi_sector));
}
EXPORT_SYMBOL(bio_add_page);
diff --git a/block/blk-settings.c b/block/blk-settings.c
index 5d21239..a2b9cb1 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -113,6 +113,7 @@
lim->seg_boundary_mask = BLK_SEG_BOUNDARY_MASK;
lim->max_segment_size = BLK_MAX_SEGMENT_SIZE;
lim->max_sectors = lim->max_hw_sectors = BLK_SAFE_MAX_SECTORS;
+ lim->chunk_sectors = 0;
lim->max_write_same_sectors = 0;
lim->max_discard_sectors = 0;
lim->discard_granularity = 0;
@@ -277,6 +278,23 @@
EXPORT_SYMBOL(blk_queue_max_hw_sectors);
/**
+ * blk_queue_chunk_sectors - set size of the chunk for this queue
+ * @q: the request queue for the device
+ * @chunk_sectors: chunk sectors in the usual 512b unit
+ *
+ * Description:
+ * If a driver doesn't want IOs to cross a given chunk size, it can set
+ * this limit and prevent merging across chunks. Note that the chunk size
+ * must currently be a power-of-2 in sectors.
+ **/
+void blk_queue_chunk_sectors(struct request_queue *q, unsigned int chunk_sectors)
+{
+ BUG_ON(!is_power_of_2(chunk_sectors));
+ q->limits.chunk_sectors = chunk_sectors;
+}
+EXPORT_SYMBOL(blk_queue_chunk_sectors);
+
+/**
* blk_queue_max_discard_sectors - set max sectors for a single discard
* @q: the request queue for the device
* @max_discard_sectors: maximum number of sectors to discard
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 3cd426e..dc2c703 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -280,6 +280,7 @@
unsigned long seg_boundary_mask;
unsigned int max_hw_sectors;
+ unsigned int chunk_sectors;
unsigned int max_sectors;
unsigned int max_segment_size;
unsigned int physical_block_size;
@@ -910,6 +911,20 @@
return q->limits.max_sectors;
}
+/*
+ * Return maximum size of a request at given offset. Only valid for
+ * file system requests.
+ */
+static inline unsigned int blk_max_size_offset(struct request_queue *q,
+ sector_t offset)
+{
+ if (!q->limits.chunk_sectors)
+ return q->limits.max_hw_sectors;
+
+ return q->limits.chunk_sectors -
+ (offset & (q->limits.chunk_sectors - 1));
+}
+
static inline unsigned int blk_rq_get_max_sectors(struct request *rq)
{
struct request_queue *q = rq->q;
@@ -917,7 +932,11 @@
if (unlikely(rq->cmd_type == REQ_TYPE_BLOCK_PC))
return q->limits.max_hw_sectors;
- return blk_queue_get_max_sectors(q, rq->cmd_flags);
+ if (!q->limits.chunk_sectors)
+ return blk_queue_get_max_sectors(q, rq->cmd_flags);
+
+ return min(blk_max_size_offset(q, blk_rq_pos(rq)),
+ blk_queue_get_max_sectors(q, rq->cmd_flags));
}
static inline unsigned int blk_rq_count_bios(struct request *rq)
@@ -983,6 +1002,7 @@
extern void blk_queue_bounce_limit(struct request_queue *, u64);
extern void blk_limits_max_hw_sectors(struct queue_limits *, unsigned int);
extern void blk_queue_max_hw_sectors(struct request_queue *, unsigned int);
+extern void blk_queue_chunk_sectors(struct request_queue *, unsigned int);
extern void blk_queue_max_segments(struct request_queue *, unsigned short);
extern void blk_queue_max_segment_size(struct request_queue *, unsigned int);
extern void blk_queue_max_discard_sectors(struct request_queue *q,