Re: v4.9, 4.4-final: 28 bioset threads on small notebook, 36 threads on cellphone

[Mike Galbraith <efault@gmx.de>]

On Tue, 2017-02-07 at 19:58 -0900, Kent Overstreet wrote:
> On Tue, Feb 07, 2017 at 09:39:11PM +0100, Pavel Machek wrote:
> > On Mon 2017-02-06 17:49:06, Kent Overstreet wrote:
> > > On Mon, Feb 06, 2017 at 04:47:24PM -0900, Kent Overstreet wrote:
> > > > On Mon, Feb 06, 2017 at 01:53:09PM +0100, Pavel Machek wrote:
> > > > > Still there on v4.9, 36 threads on nokia n900 cellphone.
> > > > > 
> > > > > So.. what needs to be done there?
> > > 
> > > > But, I just got an idea for how to handle this that might be halfway sane, maybe
> > > > I'll try and come up with a patch...
> > > 
> > > Ok, here's such a patch, only lightly tested:
> > 
> > I guess it would be nice for me to test it... but what it is against?
> > I tried after v4.10-rc5 and linux-next, but got rejects in both cases.
> 
> Sorry, I forgot I had a few other patches in my branch that touch
> mempool/biosets code.
> 
> Also, after thinking about it more and looking at the relevant code, I'm pretty
> sure we don't need rescuer threads for block devices that just split bios - i.e.
> most of them, so I changed my patch to do that.
> 
> Tested it by ripping out the current->bio_list checks/workarounds from the
> bcache code, appears to work:

Patch killed every last one of them, but..

homer:/root # dmesg|grep WARNING
[   11.701447] WARNING: CPU: 4 PID: 801 at block/bio.c:388 bio_alloc_bioset+0x1a7/0x240
[   11.711027] WARNING: CPU: 4 PID: 801 at block/blk-core.c:2013 generic_make_request+0x191/0x1f0
[   19.728989] WARNING: CPU: 0 PID: 717 at block/bio.c:388 bio_alloc_bioset+0x1a7/0x240
[   19.737020] WARNING: CPU: 0 PID: 717 at block/blk-core.c:2013 generic_make_request+0x191/0x1f0
[   19.746173] WARNING: CPU: 0 PID: 717 at block/bio.c:388 bio_alloc_bioset+0x1a7/0x240
[   19.755260] WARNING: CPU: 0 PID: 717 at block/blk-core.c:2013 generic_make_request+0x191/0x1f0
[   19.763837] WARNING: CPU: 0 PID: 717 at block/bio.c:388 bio_alloc_bioset+0x1a7/0x240
[   19.772526] WARNING: CPU: 0 PID: 717 at block/blk-core.c:2013 generic_make_request+0x191/0x1f0