Messages in this thread |  | | Date | Wed, 27 Feb 2019 09:35:56 +0800 | From | Ming Lei <> | Subject | Re: [PATCH v7 21/23] block: Avoid that flushing triggers a lockdep complaint |
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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
Thanks, Ming
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