On Wed, Feb 27, 2019 at 03:24:51PM +0100, Peter Zijlstra wrote: > 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 ?
The recursion is nvme-loop specific, see the following link: https://marc.info/?l=linux-block&m=155003205030566&w=2 Thanks, Ming
