On 2021-02-19 03:10, Mike Kravetz wrote:

Those counts will be wrong as there are no huge pages on the node.

I'll think about this more tomorrow.
Pretty sure this is an issue, but I could be wrong.  Just wanted to 
give
a heads up.

Yes, this is a problem, although the fixup would be to check whether we 
have any hugepages.

Nevertheless, I think we should not be touching surplus at all but 
rather make the page temporary.
I am exploring making migrate_pages() handle free hugepages as Michal 
suggested, so the approach is cleaner and we do not need extra 
functions. I yet have to see if that is feasible, as some issues come to 
my mind like the page needs to be in a list to go to migrate_pages, but 
if it is in that list, it is not in hugepages_freelist, and that could 
disrupt userspace as it could not dequeue hugepages if it demands it.
I have to check. Shoult not be possible, we can always make the page 
temporary here.

--
Mike Kravetz

quoted

+		}
+	}
+
+	return ret;
+}
+
+bool isolate_or_dissolve_huge_page(struct page *page)
+{
+	struct hstate *h = NULL;
+	struct page *head;
+	bool ret = false;
+
+	spin_lock(&hugetlb_lock);
+	if (PageHuge(page)) {
+		head = compound_head(page);
+		h = page_hstate(head);
+	}
+	spin_unlock(&hugetlb_lock);
+
+	/*
+	 * The page might have been dissolved from under our feet.
+	 * If that is the case, return success as if we dissolved it 
ourselves.
+	 */
+	if (!h)
+		return true;
+
+	/*
+	 * Fence off gigantic pages as there is a cyclic dependency
+	 * between alloc_contig_range and them.
+	 */
+	if (hstate_is_gigantic(h))
+		return ret;
+
+	if(!page_count(head) && alloc_and_dissolve_huge_page(h, head))
+		ret = true;
+
+	return ret;
+}
+
 struct page *alloc_huge_page(struct vm_area_struct *vma,
 				    unsigned long addr, int avoid_reserve)
 {

-- 
Oscar Salvador
SUSE L3