[PATCH 08/12] hugetlb: batch freeing of vmemmap pages

[Mike Kravetz]

Now that batching of hugetlb vmemmap optimization processing is possible,
batch the freeing of vmemmap pages.  When freeing vmemmap pages for a
hugetlb page, we add them to a list that is freed after the entire batch
has been processed.

This enhances the ability to return contiguous ranges of memory to the
low level allocators.

Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
---
 mm/hugetlb_vmemmap.c | 56 ++++++++++++++++++++++++++++++++------------
 1 file changed, 41 insertions(+), 15 deletions(-)

diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index d5e6b6c76dce..e390170c0887 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -305,11 +305,14 @@ static void vmemmap_restore_pte(pte_t *pte, unsigned long addr,
  * @end:	end address of the vmemmap virtual address range that we want to
  *		remap.
  * @reuse:	reuse address.
+ * @bulk_pages: list to deposit vmemmap pages to be freed in bulk operations
+ *		or NULL in non-bulk case;
  *
  * Return: %0 on success, negative error code otherwise.
  */
 static int vmemmap_remap_free(unsigned long start, unsigned long end,
-			      unsigned long reuse)
+			      unsigned long reuse,
+			      struct list_head *bulk_pages)
 {
 	int ret;
 	LIST_HEAD(vmemmap_pages);
@@ -372,7 +375,14 @@ static int vmemmap_remap_free(unsigned long start, unsigned long end,
 	}
 	mmap_read_unlock(&init_mm);
 
-	free_vmemmap_page_list(&vmemmap_pages);
+	/*
+	 * if performing bulk operation, do not free pages here.
+	 * rather add them to the bulk list
+	 */
+	if (!bulk_pages)
+		free_vmemmap_page_list(&vmemmap_pages);
+	else
+		list_splice(&vmemmap_pages, bulk_pages);
 
 	return ret;
 }
@@ -546,17 +556,9 @@ static bool vmemmap_should_optimize(const struct hstate *h, const struct page *h
 	return true;
 }
 
-/**
- * hugetlb_vmemmap_optimize - optimize @head page's vmemmap pages.
- * @h:		struct hstate.
- * @head:	the head page whose vmemmap pages will be optimized.
- *
- * This function only tries to optimize @head's vmemmap pages and does not
- * guarantee that the optimization will succeed after it returns. The caller
- * can use HPageVmemmapOptimized(@head) to detect if @head's vmemmap pages
- * have been optimized.
- */
-void hugetlb_vmemmap_optimize(const struct hstate *h, struct page *head)
+static void __hugetlb_vmemmap_optimize(const struct hstate *h,
+					struct page *head,
+					struct list_head *bulk_pages)
 {
 	unsigned long vmemmap_start = (unsigned long)head, vmemmap_end;
 	unsigned long vmemmap_reuse;
@@ -575,18 +577,42 @@ void hugetlb_vmemmap_optimize(const struct hstate *h, struct page *head)
 	 * to the page which @vmemmap_reuse is mapped to, then free the pages
 	 * which the range [@vmemmap_start, @vmemmap_end] is mapped to.
 	 */
-	if (vmemmap_remap_free(vmemmap_start, vmemmap_end, vmemmap_reuse))
+	if (vmemmap_remap_free(vmemmap_start, vmemmap_end, vmemmap_reuse, bulk_pages))
 		static_branch_dec(&hugetlb_optimize_vmemmap_key);
 	else
 		SetHPageVmemmapOptimized(head);
 }
 
+/**
+ * hugetlb_vmemmap_optimize - optimize @head page's vmemmap pages.
+ * @h:		struct hstate.
+ * @head:	the head page whose vmemmap pages will be optimized.
+ *
+ * This function only tries to optimize @head's vmemmap pages and does not
+ * guarantee that the optimization will succeed after it returns. The caller
+ * can use HPageVmemmapOptimized(@head) to detect if @head's vmemmap pages
+ * have been optimized.
+ */
+void hugetlb_vmemmap_optimize(const struct hstate *h, struct page *head)
+{
+	__hugetlb_vmemmap_optimize(h, head, NULL);
+}
+
+void hugetlb_vmemmap_optimize_bulk(const struct hstate *h, struct page *head,
+			struct list_head *bulk_pages)
+{
+	__hugetlb_vmemmap_optimize(h, head, bulk_pages);
+}
+
 void hugetlb_vmemmap_optimize_folios(struct hstate *h, struct list_head *folio_list)
 {
 	struct folio *folio;
+	LIST_HEAD(vmemmap_pages);
 
 	list_for_each_entry(folio, folio_list, lru)
-		hugetlb_vmemmap_optimize(h, &folio->page);
+		hugetlb_vmemmap_optimize_bulk(h, &folio->page, &vmemmap_pages);
+
+	free_vmemmap_page_list(&vmemmap_pages);
 }
 
 static struct ctl_table hugetlb_vmemmap_sysctls[] = {
-- 
2.41.0