Re: [PATCH 0/6] mm: make movable onlining suck less

[Michal Hocko]

On Thu 06-04-17 10:46:53, Reza Arbab wrote:
> On Thu, Apr 06, 2017 at 05:41:28PM +0200, Michal Hocko wrote:
> >On Thu 06-04-17 10:24:49, Reza Arbab wrote:
> >>On Thu, Apr 06, 2017 at 03:08:46PM +0200, Michal Hocko wrote:
> >>>OK, so after recent change mostly driven by testing from Reza Arbab
> >>>(thanks again) I believe I am getting to a working state finally. All I
> >>>currently have is
> >>>in git://git.kernel.org/pub/scm/linux/kernel/git/mhocko/mm.git tree
> >>>attempts/rewrite-mem_hotplug-WIP branch. I will highly appreciate more
> >>>testing of course and if there are no new issues found I will repost the
> >>>series for the review.
> >>
> >>Looking good! I can do my add/remove/repeat test and things seem fine.
> >>
> >>One thing--starting on the second iteration, I am seeing the WARN in
> >>free_area_init_node();
> >>
> >>add_memory
> >> add_memory_resource
> >>   hotadd_new_pgdat
> >>     free_area_init_node
> >>	WARN_ON(pgdat->nr_zones || pgdat->kswapd_classzone_idx);
> >
> >Have you tested with my attempts/rewrite-mem_hotplug-WIP mentioned
> >elsewhere? Because I suspect that "mm: get rid of zone_is_initialized"
> >might cause this.
> 
> This was my first time using your git branch instead of applying the patches
> from this thread to v4.11-rc5 myself.

OK, so this looks like another thing to resolve. I have seen this
warning as well but I didn't consider it relevant because I had to tweak
the code make the node go offline (removed check_and_unmap_cpu_on_node
from try_offline_node) so I thought it was a fallout from there. 

But let's have a look. hotadd_new_pgdat does for an existing pgdat
		/* Reset the nr_zones, order and classzone_idx before reuse */
		pgdat->nr_zones = 0;
		pgdat->kswapd_order = 0;
		pgdat->kswapd_classzone_idx = MAX_NR_ZONES;

so free_area_init_node absolutely has to hit this warning. This is not
in the Linus tree because it is still in Andrew's mmotm coming from
http://www.ozlabs.org/~akpm/mmotm/broken-out/mm-vmscan-prevent-kswapd-sleeping-prematurely-due-to-mismatched-classzone_idx.patch

So yay, finally that doesn't come from me. Mel, I guess that either
hotadd_new_pgdat should keep its kswapd_classzone_idx = 0 or the warning
should be updated.

-- 
Michal Hocko
SUSE Labs