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 > machine 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... http://lkml.kernel.org/r/201411231349.CAG78628.VFQFOtOSFJMOLH@xxxxxxxxxxxxxxxxxxx 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 > me. Can't we have a waitqueue like http://lkml.kernel.org/r/201510142121.IDE86954.SOVOFFQOFMJHtL@xxxxxxxxxxxxxxxxxxx ? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>