Re: Sleeping BUG in khugepaged for i586

Michal Hocko
2017-06-15T08:32:30Z

On Wed 14-06-17 18:12:06, David Rientjes wrote:
> On Thu, 8 Jun 2017, Michal Hocko wrote:
>
> > collapse_huge_page
> > pte_offset_map
> > kmap_atomic
> > kmap_atomic_prot
> > preempt_disable
> > __collapse_huge_page_copy
> > pte_unmap
> > kunmap_atomic
> > __kunmap_atomic
> > preempt_enable
> >
> > I suspect, so cond_resched seems indeed inappropriate on 32b systems.
> >
>
> Seems to be an issue for i386 and arm with ARM_LPAE. I'm slightly
> surprised we can get away with __collapse_huge_page_swapin() for
> VM_FAULT_RETRY, unless that hasn't been encountered yet.

I do not see what you mean here or how is it related.
__collapse_huge_page_swapin is called outside of
pte_offset_map/pte_unmap section

> I think the cond_resched() in __collapse_huge_page_copy() could be
> done only for !in_atomic() if we choose.

in_atomic() depends on having PREEMPT_COUNT enabled to work properly AFAIR.
I haven't double checked and something might have changed since I've
looked the last time.

--
Michal Hocko
SUSE Labs