Re: [BUG] Make setup_zone_migrate_reserve() aware of overlapping nodes

Dave Hansen
2008-08-20T18:14:37Z

On Wed, 2008-08-20 at 12:08 -0500, Adam Litke wrote:
> I have gotten to the root cause of the hugetlb badness I reported back
> on August 15th. My system has the following memory topology (note the
> overlapping node):
>
> i>>?Node 0 Memory: 0x8000000-0x44000000
> i>>?Node 1 Memory: 0x0-0x8000000 0x44000000-0x80000000
>
> setup_zone_migrate_reserve() scans the address range 0x0-0x8000000
> looking for a pageblock to move onto the MIGRATE_RESERVE list. Finding
> no candidates, it happily continues the scan into 0x8000000-0x44000000.
> When a pageblock is found, the pages are moved to the MIGRATE_RESERVE
> list on the wrong zone. Oops.

This eventually gets down into move_freepages() via:

->setup_zone_migrate_reserve()
->move_freepages_block()
->move_freepages()
right?

It looks like there have been bugs in this area before in
move_freepages(). Should there be a more stringent check in *there*?
Maybe a warning?
> i>>?
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2512,6 +2512,10 @@ static void setup_zone_migrate_reserve(struct
> zone *zone)
> pageblock_order;
>
> for (pfn = start_pfn; pfn < end_pfn; pfn += pageblock_nr_pages) {
> + /* Watch out for overlapping nodes */
> + if (!early_pfn_in_nid(pfn, zone->node))
> + continue;

zone->node doesn't exist on !CONFIG_NUMA. :(

You probably want:

if (!early_pfn_in_nid(pfn, zone_to_nid(zone)))
continue;

Are you sure you need the "early_" variant here? We're not using
early_pfn_valid() right below it. I guess you could also use:

if (!page_to_nid(page) != zone_to_nid(zone))
continue;

-- Dave