On Tue, Mar 06, 2012 at 12:19:30AM +0100, Andrea Righi wrote: > On Mon, Mar 05, 2012 at 02:30:29PM -0800, Fengguang Wu wrote: > > On Mon, Mar 05, 2012 at 04:11:15PM -0500, Vivek Goyal wrote: > ... > > > But looks like we don't much choice. As buffered writes can be controlled > > > at two levels, we probably need two knobs. Also controlling writes while > > > entring cache limits will be global and not per device (unlinke currnet > > > per device limit in blkio controller). Having separate control for "dirty > > > rate limit" leaves the scope for implementing write control at device > > > level in the future (As some people prefer that). In possibly two > > > solutions can co-exist in future. > > > > Good point. balance_dirty_pages() has no idea about the devices at > > all. So the rate limit for buffered writes can hardly be unified with > > the per-device rate limit for direct writes. > > > > I think balance_dirty_pages() can have an idea about devices. We can get > a reference to the right block device / request queue from the > address_space: > > bdev = mapping->host->i_sb->s_bdev; > q = bdev_get_queue(bdev); > > (NULL pointer dereferences apart). Problem is, there is no general 1:1 mapping between bdev and disks. For the single disk multpile partitions (sda1, sda2...) case, the above scheme is fine and makes the throttle happen at sda granularity. However for md/dm etc. there is no way (or need?) to reach the exact disk that current blkcg is operating on. Thanks, Fengguang -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
