Re: [BUG] mm, thp: khugepaged can't allocate on requested node when confined to a cpuset

[Peter Zijlstra]

On Wed, Oct 08, 2014 at 02:10:50PM -0500, Alex Thorlton wrote:

> Is this particular bug a known issue?

Its not unexpected for me.

> I've been trying to come up with
> a simple way to fix the bug, but it's a bit difficult since we no longer
> have a way to trace back to the task_struct that we're collapsing for
> once we've reached get_page_from_freelist.  I'm wondering if we might
> want to make the cpuset check higher up in the call-chain and then pass
> that nodemask down instead of sending a NULL nodemask, as we end up
> doing in many (most?) situations.  I can think of several problems with
> that approach as well, but it's all I've come up with so far.
> 
> The obvious workaround is to not isolate khugepaged to a cpuset, but
> since we're allowed to do so, I think the thread should probably behave
> appropriately when pinned to a cpuset.
> 
> Any input on this issue is greatly appreciated.  Thanks, guys!

So for the numa thing we do everything from the affected tasks context.
There was a lot of arguments early on that that could never really work,
but here we are.

Should we convert khugepaged to the same? Drive the whole thing from
task_work? That would make this issue naturally go away.
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