[PATCH 4/8] hugetlb: add hugetlb demote page support

Mike Kravetz
2021-08-16T22:51:08Z

Demote page functionality will split a huge page into a number of huge
pages of a smaller size. For example, on x86 a 1GB huge page can be
demoted into 512 2M huge pages. Demotion is done 'in place' by simply
splitting the huge page.

Added '*_for_demote' wrappers for remove_hugetlb_page,
destroy_compound_gigantic_page and prep_compound_gigantic_page for use
by demote code.

Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
---
mm/hugetlb.c | 76 +++++++++++++++++++++++++++++++++++++++++++++++++---
1 file changed, 73 insertions(+), 3 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 2f2d5002fe73..6d43523a1a4d 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1289,6 +1289,12 @@ static void destroy_compound_gigantic_page(struct page *page,
__destroy_compound_gigantic_page(page, order, false);
}

+static void destroy_compound_gigantic_page_for_demote(struct page *page,
+ unsigned int order)
+{
+ __destroy_compound_gigantic_page(page, order, true);
+}
+
static void free_gigantic_page(struct page *page, unsigned int order)
{
#ifdef CONFIG_CMA
@@ -1428,6 +1434,12 @@ static void remove_hugetlb_page(struct hstate *h, struct page *page,
__remove_hugetlb_page(h, page, adjust_surplus, false);
}

+static void remove_hugetlb_page_for_demote(struct hstate *h, struct page *page,
+ bool adjust_surplus)
+{
+ __remove_hugetlb_page(h, page, adjust_surplus, true);
+}
+
static void add_hugetlb_page(struct hstate *h, struct page *page,
bool adjust_surplus)
{
@@ -1777,6 +1789,12 @@ static bool prep_compound_gigantic_page(struct page *page, unsigned int order)
return __prep_compound_gigantic_page(page, order, false);
}

+static bool prep_compound_gigantic_page_for_demote(struct page *page,
+ unsigned int order)
+{
+ return __prep_compound_gigantic_page(page, order, true);
+}
+
/*
* PageHuge() only returns true for hugetlbfs pages, but not for normal or
* transparent huge pages. See the PageTransHuge() documentation for more
@@ -3294,9 +3312,55 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
return 0;
}

+static int demote_free_huge_page(struct hstate *h, struct page *page)
+{
+ int i, nid = page_to_nid(page);
+ struct hstate *target_hstate;
+ bool cma_page = HPageCma(page);
+
+ target_hstate = size_to_hstate(PAGE_SIZE << h->demote_order);
+
+ remove_hugetlb_page_for_demote(h, page, false);
+ spin_unlock_irq(&hugetlb_lock);
+
+ if (alloc_huge_page_vmemmap(h, page)) {
+ /* Allocation of vmemmmap failed, we can not demote page */
+ spin_lock_irq(&hugetlb_lock);
+ set_page_refcounted(page);
+ add_hugetlb_page(h, page, false);
+ return 1;
+ }
+
+ /*
+ * Use destroy_compound_gigantic_page_for_demote for all huge page
+ * sizes as it will not ref count pages.
+ */
+ destroy_compound_gigantic_page_for_demote(page, huge_page_order(h));
+
+ for (i = 0; i < pages_per_huge_page(h);
+ i += pages_per_huge_page(target_hstate)) {
+ if (hstate_is_gigantic(target_hstate))
+ prep_compound_gigantic_page_for_demote(page + i,
+ target_hstate->order);
+ else
+ prep_compound_page(page + i, target_hstate->order);
+ set_page_private(page + i, 0);
+ set_page_refcounted(page + i);
+ prep_new_huge_page(target_hstate, page + i, nid);
+ if (cma_page)
+ SetHPageCma(page + i);
+ put_page(page + i);
+ }
+
+ spin_lock_irq(&hugetlb_lock);
+ return 0;
+}
+
static int demote_pool_huge_page(struct hstate *h, nodemask_t *nodes_allowed)
__must_hold(&hugetlb_lock)
{
+ int nr_nodes, node;
+ struct page *page;
int rc = 0;

lockdep_assert_held(&hugetlb_lock);
@@ -3312,9 +3376,15 @@ static int demote_pool_huge_page(struct hstate *h, nodemask_t *nodes_allowed)
return 1;
}

- /*
- * TODO - demote fucntionality will be added in subsequent patch
- */
+ for_each_node_mask_to_free(h, nr_nodes, node, nodes_allowed) {
+ if (!list_empty(&h->hugepage_freelists[node])) {
+ page = list_entry(h->hugepage_freelists[node].next,
+ struct page, lru);
+ rc = !demote_free_huge_page(h, page);
+ break;
+ }
+ }
+
return rc;
}

--
2.31.1