[PATCH v9 05/11] mm/hugetlb: Allocate the vmemmap pages associated with each HugeTLB page

[Muchun Song <songmuchun@bytedance.com>]

When we free a HugeTLB page to the buddy allocator, we should allocate the
vmemmap pages associated with it. We can do that in the __free_hugepage()
before freeing it to buddy.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 include/linux/mm.h   |  1 +
 mm/hugetlb.c         |  2 ++
 mm/hugetlb_vmemmap.c | 11 +++++++++
 mm/hugetlb_vmemmap.h |  5 ++++
 mm/sparse-vmemmap.c  | 69 +++++++++++++++++++++++++++++++++++++++++++++++++++-
 5 files changed, 87 insertions(+), 1 deletion(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index ab02e405a979..5b8dc36e4d20 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -3006,6 +3006,7 @@ static inline void print_vma_addr(char *prefix, unsigned long rip)
 #endif
 
 void vmemmap_remap_reuse(unsigned long start, unsigned long size);
+void vmemmap_remap_restore(unsigned long start, unsigned long size);
 
 void *sparse_buffer_alloc(unsigned long size);
 struct page * __populate_section_memmap(unsigned long pfn,
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 0ff9b90e524f..542e6cb81321 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1362,6 +1362,8 @@ static void __free_hugepage(struct hstate *h, struct page *page)
 {
 	int i;
 
+	alloc_huge_page_vmemmap(h, page);
+
 	for (i = 0; i < pages_per_huge_page(h); i++) {
 		page[i].flags &= ~(1 << PG_locked | 1 << PG_error |
 				1 << PG_referenced | 1 << PG_dirty |
diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index 6d4e77a2b6c7..02201c2e3dfa 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -185,6 +185,17 @@ static inline unsigned long free_vmemmap_pages_size_per_hpage(struct hstate *h)
 	return (unsigned long)free_vmemmap_pages_per_hpage(h) << PAGE_SHIFT;
 }
 
+void alloc_huge_page_vmemmap(struct hstate *h, struct page *head)
+{
+	unsigned long vmemmap_addr = (unsigned long)head;
+
+	if (!free_vmemmap_pages_per_hpage(h))
+		return;
+
+	vmemmap_remap_restore(vmemmap_addr + RESERVE_VMEMMAP_SIZE,
+			      free_vmemmap_pages_size_per_hpage(h));
+}
+
 void free_huge_page_vmemmap(struct hstate *h, struct page *head)
 {
 	unsigned long vmemmap_addr = (unsigned long)head;
diff --git a/mm/hugetlb_vmemmap.h b/mm/hugetlb_vmemmap.h
index 01f8637adbe0..b2c8d2f11d48 100644
--- a/mm/hugetlb_vmemmap.h
+++ b/mm/hugetlb_vmemmap.h
@@ -11,6 +11,7 @@
 #include <linux/hugetlb.h>
 
 #ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
+void alloc_huge_page_vmemmap(struct hstate *h, struct page *head);
 void free_huge_page_vmemmap(struct hstate *h, struct page *head);
 
 /*
@@ -25,6 +26,10 @@ static inline unsigned int free_vmemmap_pages_per_hpage(struct hstate *h)
 	return 0;
 }
 #else
+static inline void alloc_huge_page_vmemmap(struct hstate *h, struct page *head)
+{
+}
+
 static inline void free_huge_page_vmemmap(struct hstate *h, struct page *head)
 {
 }
diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
index 78c527617e8d..ffcf092c92ed 100644
--- a/mm/sparse-vmemmap.c
+++ b/mm/sparse-vmemmap.c
@@ -29,6 +29,7 @@
 #include <linux/sched.h>
 #include <linux/pgtable.h>
 #include <linux/bootmem_info.h>
+#include <linux/delay.h>
 
 #include <asm/dma.h>
 #include <asm/pgalloc.h>
@@ -39,7 +40,8 @@
  *
  * @rmap_pte:		called for each non-empty PTE (lowest-level) entry.
  * @reuse:		the page which is reused for the tail vmemmap pages.
- * @vmemmap_pages:	the list head of the vmemmap pages that can be freed.
+ * @vmemmap_pages:	the list head of the vmemmap pages that can be freed
+ *			or is mapped from.
  */
 struct vmemmap_rmap_walk {
 	void (*rmap_pte)(pte_t *pte, unsigned long addr,
@@ -54,6 +56,9 @@ struct vmemmap_rmap_walk {
  */
 #define VMEMMAP_TAIL_PAGE_REUSE		-1
 
+/* The gfp mask of allocating vmemmap page */
+#define GFP_VMEMMAP_PAGE	(GFP_KERNEL | __GFP_RETRY_MAYFAIL | __GFP_NOWARN)
+
 static void vmemmap_pte_range(pmd_t *pmd, unsigned long addr,
 			      unsigned long end, struct vmemmap_rmap_walk *walk)
 {
@@ -200,6 +205,68 @@ void vmemmap_remap_reuse(unsigned long start, unsigned long size)
 	free_vmemmap_page_list(&vmemmap_pages);
 }
 
+static void vmemmap_remap_restore_pte(pte_t *pte, unsigned long addr,
+				      struct vmemmap_rmap_walk *walk)
+{
+	pgprot_t pgprot = PAGE_KERNEL;
+	struct page *page;
+	void *to;
+
+	BUG_ON(pte_page(*pte) != walk->reuse);
+
+	page = list_first_entry(walk->vmemmap_pages, struct page, lru);
+	list_del(&page->lru);
+	to = page_to_virt(page);
+	copy_page(to, page_to_virt(walk->reuse));
+
+	set_pte_at(&init_mm, addr, pte, mk_pte(page, pgprot));
+}
+
+static void alloc_vmemmap_page_list(struct list_head *list,
+				    unsigned long nr_pages)
+{
+	while (nr_pages--) {
+		struct page *page;
+
+retry:
+		page = alloc_page(GFP_VMEMMAP_PAGE);
+		if (unlikely(!page)) {
+			msleep(100);
+			/*
+			 * We should retry infinitely, because we cannot
+			 * handle allocation failures. Once we allocate
+			 * vmemmap pages successfully, then we can free
+			 * a HugeTLB page.
+			 */
+			goto retry;
+		}
+		list_add_tail(&page->lru, list);
+	}
+}
+
+/**
+ * vmemmap_remap_restore - remap the vmemmap virtual address range
+ *                         [start, start + size) to the page respectively
+ *                         which from the @vmemmap_pages
+ * @start:	start address of the vmemmap virtual address range
+ * @end:	size of the vmemmap virtual address range
+ */
+void vmemmap_remap_restore(unsigned long start, unsigned long size)
+{
+	LIST_HEAD(vmemmap_pages);
+	unsigned long end = start + size;
+
+	struct vmemmap_rmap_walk walk = {
+		.rmap_pte	= vmemmap_remap_restore_pte,
+		.vmemmap_pages	= &vmemmap_pages,
+	};
+
+	might_sleep();
+
+	alloc_vmemmap_page_list(&vmemmap_pages, size >> PAGE_SHIFT);
+	vmemmap_remap_range(start, end, &walk);
+}
+
 /*
  * Allocate a block of memory to be used to back the virtual memory map
  * or to back the page tables that are used to create the mapping.
-- 
2.11.0