Re: [PATCH v2 2/2] mm: hugetlb: support gigantic surplus pages

[Huang Shijie <shijie.huang@arm.com>]

On Wed, Nov 09, 2016 at 04:55:49PM +0100, Gerald Schaefer wrote:
> > index 9fdfc24..5dbfd62 100644
> > --- a/mm/hugetlb.c
> > +++ b/mm/hugetlb.c
> > @@ -1095,6 +1095,9 @@ static struct page *alloc_gigantic_page(int nid, unsigned int order)
> >  	unsigned long ret, pfn, flags;
> >  	struct zone *z;
> > 
> > +	if (nid == NUMA_NO_NODE)
> > +		nid = numa_mem_id();
> > +
> 
> Now counter.sh works (on s390) w/o the lockdep warning. However, it looks
Good news to me :)
We have found the root cause of the s390 issue.

> like this change will now result in inconsistent behavior compared to the
> normal sized hugepages, regarding surplus page allocation. Setting nid to
> numa_mem_id() means that only the node of the current CPU will be considered
> for allocating a gigantic page, as opposed to just "preferring" the current
> node in the normal size case (__hugetlb_alloc_buddy_huge_page() ->
> alloc_pages_node()) with a fallback to using other nodes.
Yes.

> 
> I am not really familiar with NUMA, and I might be wrong here, but if
> this is true then gigantic pages, which may be hard allocate at runtime
> in general, will be even harder to find (as surplus pages) because you
> only look on the current node.
Okay, I will try to fix this in the next version.

> 
> I honestly do not understand why alloc_gigantic_page() needs a nid
> parameter at all, since it looks like it will only be called from
> alloc_fresh_gigantic_page_node(), which in turn is only called
> from alloc_fresh_gigantic_page() in a "for_each_node" loop (at least
> before your patch).
> 
> Now it could be an option to also use alloc_fresh_gigantic_page()
> in your patch, instead of directly calling alloc_gigantic_page(),
Yes, a good suggestion. But I need to do some change to the
alloc_fresh_gigantic_page().	


Thanks
Huang Shijie

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