For things like NBD we want to be able to experiment with different sized requests going over the wire. Half of our limit is controled by max_sectors_kb, but the other half is how many bvec's we can cram into a request, which is controlled by max_segments. Changing this sysfs knob to be writeable allows us to be able to control our io limits more precisely.
Signed-off-by: Josef Bacik <[email protected]> --- block/blk-sysfs.c | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-) diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c index 4585426..e7db3f8 100644 --- a/block/blk-sysfs.c +++ b/block/blk-sysfs.c @@ -116,6 +116,19 @@ static ssize_t queue_max_sectors_show(struct request_queue *q, char *page) return queue_var_show(max_sectors_kb, (page)); } +static ssize_t queue_max_segments_store(struct request_queue *q, + const char *page, size_t count) +{ + unsigned long max_segments; + ssize_t ret = queue_var_store(&max_segments, page, count); + + if (ret < 0) + return ret; + + q->limits.max_segments = (short)max_segments; + return ret; +} + static ssize_t queue_max_segments_show(struct request_queue *q, char *page) { return queue_var_show(queue_max_segments(q), (page)); @@ -527,8 +540,9 @@ static struct queue_sysfs_entry queue_max_hw_sectors_entry = { }; static struct queue_sysfs_entry queue_max_segments_entry = { - .attr = {.name = "max_segments", .mode = S_IRUGO }, + .attr = {.name = "max_segments", .mode = S_IRUGO | S_IWUSR }, .show = queue_max_segments_show, + .store = queue_max_segments_store, }; static struct queue_sysfs_entry queue_max_discard_segments_entry = { -- 2.7.4
