nbd: increase default and max request sizes

Raise the default max request size for nbd to 128KB (from 127KB) to get it
4KB aligned.  This patch also allows the max request size to be increased
(via /sys/block/nbd<x>/queue/max_sectors_kb) to 32MB.

The patch makes nbd network traffic more efficient by:
- reducing request fragmentation (4KB alignment)
- reducing the number of requests (fewer round trips, less network overhead)

Especially in high latency networks, larger request size can make a dramatic

Signed-off-by: Paul Clements <paul.clements@steeleye.com>
Signed-off-by: Michal Belczyk <belczyk@bsd.krakow.pl>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index 7fecc784be01321cf0954024252e47fa777eb763..037288e7874d625676f5fa9e95a9920ac91551f5 100644 (file)
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -856,6 +856,8 @@ static int __init nbd_init(void)
                disk->queue->limits.discard_granularity = 512;
                disk->queue->limits.max_discard_sectors = UINT_MAX;
                disk->queue->limits.discard_zeroes_data = 0;
+               blk_queue_max_hw_sectors(disk->queue, 65536);
+               disk->queue->limits.max_sectors = 256;
        }
 
        if (register_blkdev(NBD_MAJOR, "nbd")) {