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Re: [PATCH] workqueue: warn if memory reclaim tries to flush !WQ_MEM_RECLAIM workqueue

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On Thu, Dec 03, 2015 at 03:56:32PM -0500, Tejun Heo wrote:
> So, if I'm not mistaken, those are all marking tasks which can be
> depended upon during memory reclaim and we do want to catch them all.

Up to a point yes, these are things that want to be reliable during
reclaim, but lacking memory reserves and usage bounds (which we
discussed last at lsf/mm) these are just wanna-be.

> PF_MEMALLOC shouldn't depend on something which require memory to be
> reclaimed to guarantee forward progress.

PF_MEMALLOC basically avoids reclaim for any memory allocation while its
set.

The thing is, even if your workqueue has WQ_MEM_RECLAIM set, it will not
hit the mayday button until you're completely full flat out of memory.
At which point you're probably boned anyway, because, as per the above,
all that code assumes there's _some_ memory to be had.

One solution is to always fail maybe_create_worker() when PF_MEMALLOC is
set, thus always hitting the mayday button.
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[PATCH 1/2] watchdog: introduce touch_softlockup_watchdog_sched() Tejun Heo <tj@kernel.org> - 2015-12-03 01:30 +0100
  [PATCH 2/2] workqueue: implement lockup detector Tejun Heo <tj@kernel.org> - 2015-12-03 01:30 +0100
    Re: [PATCH 2/2] workqueue: implement lockup detector Tejun Heo <tj@kernel.org> - 2015-12-03 15:50 +0100
    Re: [PATCH 2/2] workqueue: implement lockup detector Don Zickus <dzickus@redhat.com> - 2015-12-03 19:00 +0100
      Re: [PATCH 2/2] workqueue: implement lockup detector Tejun Heo <tj@kernel.org> - 2015-12-03 20:50 +0100
        Re: [PATCH 2/2] workqueue: implement lockup detector Ulrich Obergfell <uobergfe@redhat.com> - 2015-12-03 21:20 +0100
          Re: [PATCH 2/2] workqueue: implement lockup detector Tejun Heo <tj@kernel.org> - 2015-12-03 22:00 +0100
            Re: [PATCH 2/2] workqueue: implement lockup detector Ingo Molnar <mingo@kernel.org> - 2015-12-04 09:10 +0100
              Re: [PATCH 2/2] workqueue: implement lockup detector Don Zickus <dzickus@redhat.com> - 2015-12-04 18:00 +0100
            Re: [PATCH 2/2] workqueue: implement lockup detector Ulrich Obergfell <uobergfe@redhat.com> - 2015-12-04 14:30 +0100
    [PATCH v2 2/2] workqueue: implement lockup detector Tejun Heo <tj@kernel.org> - 2015-12-07 20:10 +0100
      Re: [PATCH v2 2/2] workqueue: implement lockup detector Tejun Heo <tj@kernel.org> - 2015-12-07 22:40 +0100
        Re: [PATCH v2 2/2] workqueue: implement lockup detector Don Zickus <dzickus@redhat.com> - 2015-12-08 17:10 +0100
          Re: [PATCH v2 2/2] workqueue: implement lockup detector Tejun Heo <tj@kernel.org> - 2015-12-08 17:40 +0100
      Re: [PATCH v2 2/2] workqueue: implement lockup detector Don Zickus <dzickus@redhat.com> - 2015-12-07 22:40 +0100
  Re: [PATCH 1/2] watchdog: introduce touch_softlockup_watchdog_sched() Peter Zijlstra <peterz@infradead.org> - 2015-12-03 10:40 +0100
    Re: [PATCH 1/2] watchdog: introduce touch_softlockup_watchdog_sched() Peter Zijlstra <peterz@infradead.org> - 2015-12-03 11:10 +0100
      Re: [PATCH 1/2] watchdog: introduce touch_softlockup_watchdog_sched() Tejun Heo <tj@kernel.org> - 2015-12-03 15:50 +0100
        Re: [PATCH 1/2] watchdog: introduce touch_softlockup_watchdog_sched() Tejun Heo <tj@kernel.org> - 2015-12-03 16:10 +0100
          [PATCH] workqueue: warn if memory reclaim tries to flush  !WQ_MEM_RECLAIM workqueue Tejun Heo <tj@kernel.org> - 2015-12-03 20:30 +0100
            Re: [PATCH] workqueue: warn if memory reclaim tries to flush  !WQ_MEM_RECLAIM workqueue Peter Zijlstra <peterz@infradead.org> - 2015-12-03 21:50 +0100
              Re: [PATCH] workqueue: warn if memory reclaim tries to flush  !WQ_MEM_RECLAIM workqueue Tejun Heo <tj@kernel.org> - 2015-12-03 22:00 +0100
                Re: [PATCH] workqueue: warn if memory reclaim tries to flush  !WQ_MEM_RECLAIM workqueue Peter Zijlstra <peterz@infradead.org> - 2015-12-03 22:10 +0100
                Re: [PATCH] workqueue: warn if memory reclaim tries to flush  !WQ_MEM_RECLAIM workqueue Tejun Heo <tj@kernel.org> - 2015-12-03 23:10 +0100
                Re: [PATCH] workqueue: warn if memory reclaim tries to flush  !WQ_MEM_RECLAIM workqueue Peter Zijlstra <peterz@infradead.org> - 2015-12-04 14:00 +0100
            Re: [PATCH] workqueue: warn if memory reclaim tries to flush  !WQ_MEM_RECLAIM workqueue Tejun Heo <tj@kernel.org> - 2015-12-07 17:00 +0100
        Re: [PATCH 1/2] watchdog: introduce touch_softlockup_watchdog_sched() Peter Zijlstra <peterz@infradead.org> - 2015-12-03 16:10 +0100

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