Re: [PATCH v2 00/28] The new cgroup slab memory controller

[Michal Hocko]

On Wed 02-09-20 08:51:06, Pavel Tatashin wrote:
> > > > Thread #1: memory hot-remove systemd service
> > > > Loops indefinitely, because if there is something still to be migrated
> > > > this loop never terminates. However, this loop can be terminated via
> > > > signal from systemd after timeout.
> > > > __offline_pages()
> > > >       do {
> > > >           pfn = scan_movable_pages(pfn, end_pfn);
> > > >                   # Returns 0, meaning there is nothing available to
> > > >                   # migrate, no page is PageLRU(page)
> > > >           ...
> > > >           ret = walk_system_ram_range(start_pfn, end_pfn - start_pfn,
> > > >                                             NULL, check_pages_isolated_cb);
> > > >                   # Returns -EBUSY, meaning there is at least one PFN that
> > > >                   # still has to be migrated.
> > > >       } while (ret);
> >
> 
> Hi Micahl,
> 
> > This shouldn't really happen. What does prevent from this to proceed?
> > Did you manage to catch the specific pfn and what is it used for?
> 
> I did.
> 
> > start_isolate_page_range and scan_movable_pages should fail if there is
> > any memory that cannot be migrated permanently. This is something that
> > we should focus on when debugging.
> 
> I was hitting this issue:
> mm/memory_hotplug: drain per-cpu pages again during memory offline
> https://lore.kernel.org/lkml/20200901124615.137200-1-pasha.tatashin@xxxxxxxxxx

I have noticed the patch but didn't have time to think it through (have
been few days off and catching up with emails). Will give it a higher
priority.

-- 
Michal Hocko
SUSE Labs