On Wed, Apr 05, 2017 at 01:59:49PM -0700, Hugh Dickins wrote:
> Hi Mel,
>
> I suspect that it's not safe for kthreadd to drain_all_pages();
> but I haven't studied flush_work() etc, so don't really know what
> I'm talking about: hoping that you will jump to a realization.
>
You're right, it's not safe. If kthreadd is creating the workqueue
thread to do the drain and it'll recurse into itself.
> 4.11-rc has been giving me hangs after hours of swapping load. At
> first they looked like memory leaks ("fork: Cannot allocate memory");
> but for no good reason I happened to do "cat /proc/sys/vm/stat_refresh"
> before looking at /proc/meminfo one time, and the stat_refresh stuck
> in D state, waiting for completion of flush_work like many kworkers.
> kthreadd waiting for completion of flush_work in drain_all_pages().
>
It's asking itself to do work in all likelihood.
> Patch below has been running well for 36 hours now:
> a bit too early to be sure, but I think it's time to turn to you.
>
I think the patch is valid but like Michal, would appreciate if you
could run the patch he linked to see if it also side-steps the same
problem.
Good spot!
--
Mel Gorman
SUSE Labs
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