[patch 132/262] hugetlb: add hugetlb demote page support

Andrew Morton
2021-11-05T20:41:38Z

From: Mike Kravetz <mike.kravetz@oracle.com>
Subject: hugetlb: add hugetlb demote page support

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_hugetlb_page and prep_compound_gigantic_page for use by
demote code.

[mike.kravetz@oracle.com: v4]
Link: https://lkml.kernel.org/r/6ca29b8e-527c-d6ec-900e-e6a43e4f8b73@oracle.com
Link: https://lkml.kernel.org/r/20211007181918.136982-6-mike.kravetz@oracle.com
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Cc: "Aneesh Kumar K . V" <aneesh.kumar@linux.ibm.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Naoya Horiguchi <naoya.horiguchi@linux.dev>
Cc: Nghia Le <nghialm78@gmail.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

mm/hugetlb.c | 100 +++++++++++++++++++++++++++++++++++++++++++++----
1 file changed, 92 insertions(+), 8 deletions(-)

--- a/mm/hugetlb.c~hugetlb-add-hugetlb-demote-page-support
+++ a/mm/hugetlb.c
@@ -1270,7 +1270,7 @@ static int hstate_next_node_to_free(stru
((node = hstate_next_node_to_free(hs, mask)) || 1); \
nr_nodes--)

-#ifdef CONFIG_ARCH_HAS_GIGANTIC_PAGE
+/* used to demote non-gigantic_huge pages as well */
static void __destroy_compound_gigantic_page(struct page *page,
unsigned int order, bool demote)
{
@@ -1293,6 +1293,13 @@ static void __destroy_compound_gigantic_
__ClearPageHead(page);
}

+static void destroy_compound_hugetlb_page_for_demote(struct page *page,
+ unsigned int order)
+{
+ __destroy_compound_gigantic_page(page, order, true);
+}
+
+#ifdef CONFIG_ARCH_HAS_GIGANTIC_PAGE
static void destroy_compound_gigantic_page(struct page *page,
unsigned int order)
{
@@ -1438,6 +1445,12 @@ static void remove_hugetlb_page(struct h
__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)
{
@@ -1779,6 +1792,12 @@ static bool prep_compound_gigantic_page(
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
@@ -3304,9 +3323,72 @@ out:
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;
+ int rc = 0;
+
+ target_hstate = size_to_hstate(PAGE_SIZE << h->demote_order);
+
+ remove_hugetlb_page_for_demote(h, page, false);
+ spin_unlock_irq(&hugetlb_lock);
+
+ rc = alloc_huge_page_vmemmap(h, page);
+ if (rc) {
+ /* 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 rc;
+ }
+
+ /*
+ * Use destroy_compound_hugetlb_page_for_demote for all huge page
+ * sizes as it will not ref count pages.
+ */
+ destroy_compound_hugetlb_page_for_demote(page, huge_page_order(h));
+
+ /*
+ * Taking target hstate mutex synchronizes with set_max_huge_pages.
+ * Without the mutex, pages added to target hstate could be marked
+ * as surplus.
+ *
+ * Note that we already hold h->resize_lock. To prevent deadlock,
+ * use the convention of always taking larger size hstate mutex first.
+ */
+ mutex_lock(&target_hstate->resize_lock);
+ 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);
+ put_page(page + i);
+ }
+ mutex_unlock(&target_hstate->resize_lock);
+
+ spin_lock_irq(&hugetlb_lock);
+
+ /*
+ * Not absolutely necessary, but for consistency update max_huge_pages
+ * based on pool changes for the demoted page.
+ */
+ h->max_huge_pages--;
+ target_hstate->max_huge_pages += pages_per_huge_page(h);
+
+ return rc;
+}
+
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);
@@ -3317,9 +3399,15 @@ static int demote_pool_huge_page(struct
return -EINVAL; /* internal error */
}

- /*
- * 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;
}

@@ -3554,10 +3642,6 @@ static ssize_t demote_store(struct kobje
/*
* Check for available pages to demote each time thorough the
* loop as demote_pool_huge_page will drop hugetlb_lock.
- *
- * NOTE: demote_pool_huge_page does not yet drop hugetlb_lock
- * but will when full demote functionality is added in a later
- * patch.
*/
if (nid != NUMA_NO_NODE)
nr_available = h->free_huge_pages_node[nid];
_