On Wed, Feb 27, 2019 at 09:35:56AM +0800, Ming Lei wrote: > On Tue, Feb 26, 2019 at 07:08:02PM +0100, Peter Zijlstra wrote: > > On Fri, Feb 15, 2019 at 10:26:59AM +0800, Ming Lei wrote: > > > There might be lots of blk_flush_queue instance which is allocated > > > for each hctx, then lots of class key slot may be wasted. > > > > What is 'lots' ? for someone who doesn't really know all that much about > > the block layer. > > Each hw queue has one instance of blk_flush_queue, and one device may > has lots of hw queues(may be > all possible cpus, such as nvme), and there > may be lots of block devices in one system. > > Suppose one system has 10 NVMe hosts, 8 disks attached to each host, and > 256 CPU cores in the system, there can be 10 * 8 * 256 = 20K instances of > blk_flush_queue. > > Not mention there are other block devices(loop, nbd, scsi, ...) in the system. > > That is why I suggest to use one single lock class for addressing this > nvme loop specific issue: > > https://marc.info/?l=linux-kernel&m=155019765724564&w=2
Right; that is rather a lot. But what causes the recursion, and thus how is it specific to NVME ?
