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

[Huang Shijie]

When testing the gigantic page whose order is too large for the buddy
allocator, the libhugetlbfs test case "counter.sh" will fail.

The failure is caused by:
 1) kernel fails to allocate a gigantic page for the surplus case.
    And the gather_surplus_pages() will return NULL in the end.

 2) The condition checks for "over-commit" is wrong.

This patch adds code to allocate the gigantic page in the
__alloc_huge_page(). After this patch, gather_surplus_pages()
can return a gigantic page for the surplus case.

This patch also changes the condition checks for:
     return_unused_surplus_pages()
     nr_overcommit_hugepages_store()

After this patch, the counter.sh can pass for the gigantic page.

Acked-by: Steve Capper <steve.capper at arm.com>
Signed-off-by: Huang Shijie <shijie.huang at arm.com>
---
 mm/hugetlb.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 0bf4444..2b67aff 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1574,7 +1574,7 @@ static struct page *__alloc_huge_page(struct hstate *h,
 	struct page *page;
 	unsigned int r_nid;
 
-	if (hstate_is_gigantic(h))
+	if (hstate_is_gigantic(h) && !gigantic_page_supported())
 		return NULL;
 
 	/*
@@ -1619,7 +1619,13 @@ static struct page *__alloc_huge_page(struct hstate *h,
 	}
 	spin_unlock(&hugetlb_lock);
 
-	page = __hugetlb_alloc_buddy_huge_page(h, vma, addr, nid);
+	if (hstate_is_gigantic(h))  {
+		page = alloc_gigantic_page(nid, huge_page_order(h));
+		if (page)
+			prep_compound_gigantic_page(page, huge_page_order(h));
+	} else {
+		page = __hugetlb_alloc_buddy_huge_page(h, vma, addr, nid);
+	}
 
 	spin_lock(&hugetlb_lock);
 	if (page) {
@@ -1786,8 +1792,7 @@ static void return_unused_surplus_pages(struct hstate *h,
 	/* Uncommit the reservation */
 	h->resv_huge_pages -= unused_resv_pages;
 
-	/* Cannot return gigantic pages currently */
-	if (hstate_is_gigantic(h))
+	if (hstate_is_gigantic(h) && !gigantic_page_supported())
 		return;
 
 	nr_pages = min(unused_resv_pages, h->surplus_huge_pages);
@@ -2439,7 +2444,7 @@ static ssize_t nr_overcommit_hugepages_store(struct kobject *kobj,
 	unsigned long input;
 	struct hstate *h = kobj_to_hstate(kobj, NULL);
 
-	if (hstate_is_gigantic(h))
+	if (hstate_is_gigantic(h) && !gigantic_page_supported())
 		return -EINVAL;
 
 	err = kstrtoul(buf, 10, &input);
-- 
2.1.4