Re: [PATCH] mm,vmscan: Use accurate values for zone_reclaimable()checks
From: Tetsuo Handa
Date: Tue Oct 27 2015 - 07:07:46 EST
Michal Hocko wrote:
> > On Fri, Oct 23, 2015 at 01:11:45PM +0200, Michal Hocko wrote:
> > > > The problem here is not lack
> > > > of execution resource but concurrency management misunderstanding the
> > > > situation.
> > >
> > > And this sounds like a bug to me.
> > I don't know. I can be argued either way, the other direction being a
> > kernel thread going RUNNING non-stop is buggy. Given how this has
> > been a complete non-issue for all the years, I'm not sure how useful
> > plugging this is.
> Well, I guess we haven't noticed because this is a pathological case. It
> also triggers OOM livelocks which were not reported in the past either.
> You do not reach this state normally unless you rely _want_ to kill your
I don't think we can say this is a pathological case. Customers' serves
might have hit this state. We have no code for warning this state.
> And vmstat is not the only instance. E.g. sysrq oom trigger is known
> to stay behind in similar cases. It should be changed to a dedicated
> WQ_MEM_RECLAIM wq and it would require runnable item guarantee as well.
Well, this seems to be the cause of SysRq-f being unresponsive...
Picking up from http://lkml.kernel.org/r/201506112212.JAG26531.FLSVFMOQJOtOHF@xxxxxxxxxxxxxxxxxxx
[ 515.536393] Showing busy workqueues and worker pools:
[ 515.538185] workqueue events: flags=0x0
[ 515.539758] pwq 6: cpus=3 node=0 flags=0x0 nice=0 active=8/256
[ 515.541872] pending: vmpressure_work_fn, console_callback, vmstat_update, flush_to_ldisc, push_to_pool, moom_callback, sysrq_reinject_alt_sysrq, fb_deferred_io_work
[ 515.546684] workqueue events_power_efficient: flags=0x80
[ 515.548589] pwq 6: cpus=3 node=0 flags=0x0 nice=0 active=2/256
[ 515.550829] pending: neigh_periodic_work, check_lifetime
[ 515.552884] workqueue events_freezable_power_: flags=0x84
[ 515.554742] pwq 6: cpus=3 node=0 flags=0x0 nice=0 active=1/256
[ 515.556846] in-flight: 3837:disk_events_workfn
[ 515.558665] workqueue writeback: flags=0x4e
[ 515.560291] pwq 16: cpus=0-7 flags=0x4 nice=0 active=2/256
[ 515.562271] in-flight: 3812:bdi_writeback_workfn bdi_writeback_workfn
[ 515.564544] workqueue xfs-data/sda1: flags=0xc
[ 515.566265] pwq 6: cpus=3 node=0 flags=0x0 nice=0 active=4/256
[ 515.568359] in-flight: 374(RESCUER):xfs_end_io, 3759:xfs_end_io, 26:xfs_end_io, 3836:xfs_end_io
[ 515.571018] pwq 2: cpus=1 node=0 flags=0x0 nice=0 active=1/256
[ 515.573113] in-flight: 179:xfs_end_io
[ 515.574782] pool 2: cpus=1 node=0 flags=0x0 nice=0 workers=4 idle: 3790 237 3820
[ 515.577230] pool 6: cpus=3 node=0 flags=0x0 nice=0 workers=5 manager: 219
[ 515.579488] pool 16: cpus=0-7 flags=0x4 nice=0 workers=3 idle: 356 357
We want immediate execution guarantee for not only vmstat_update and
moom_callback but also vmstat_shepherd and console_callback?
> > > Don't we have some IO related paths which would suffer from the same
> > > problem. I haven't checked all the WQ_MEM_RECLAIM users but from the
> > > name I would expect they _do_ participate in the reclaim and so they
> > > should be able to make a progress. Now if your new IMMEDIATE flag will
> > Seriously, nobody goes full-on RUNNING.
> Looping with cond_resched seems like general pattern in the kernel when
> there is no clear source to wait for. We have io_schedule when we know
> we should wait for IO (in case of congestion) but this is not necessarily
> the case - as you can see here. What should we wait for? A short nap
> without actually waiting on anything sounds like a dirty workaround to
Can't we have a waitqueue like
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