!1246 mm/hugetlb_vmemmap: remap head page to newly allocated page

Merge Pull Request from: @ci-robot 
 
PR sync from: Liu Shixin <liushixin2@huawei.com>
https://mailweb.openeuler.org/hyperkitty/list/kernel@openeuler.org/message/5RIDEB6A7NBTUWJUHQL6MOC4ZUD2N323/ 
 
 
Link:https://gitee.com/openeuler/kernel/pulls/1246 

Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com> 
Signed-off-by: Jialin Zhang <zhangjialin11@huawei.com> 

mm/sparse-vmemmap.c

@@ -221,12 +221,7 @@ static int vmemmap_remap_range(unsigned long start, unsigned long end,
 			return ret;
 	} while (pgd++, addr = next, addr != end);
 
-	/*
-	 * We only change the mapping of the vmemmap virtual address range
-	 * [@start + PAGE_SIZE, end), so we only need to flush the TLB which
-	 * belongs to the range.
-	 */
-	flush_tlb_kernel_range(start + PAGE_SIZE, end);
+	flush_tlb_kernel_range(start, end);
 
 	return 0;
 }
@@ -264,9 +259,23 @@ static void vmemmap_remap_pte(pte_t *pte, unsigned long addr,
 	 * to the tail pages.
 	 */
 	pgprot_t pgprot = PAGE_KERNEL_RO;
-	pte_t entry = mk_pte(walk->reuse_page, pgprot);
 	struct page *page = pte_page(*pte);
+	pte_t entry;
 
+	/* Remapping the head page requires r/w */
+	if (unlikely(addr == walk->reuse_addr)) {
+		pgprot = PAGE_KERNEL;
+		list_del(&walk->reuse_page->lru);
+
+		/*
+		 * Makes sure that preceding stores to the page contents from
+		 * vmemmap_remap_free() become visible before the set_pte_at()
+		 * write.
+		 */
+		smp_wmb();
+	}
+
+	entry = mk_pte(walk->reuse_page, pgprot);
 	list_add_tail(&page->lru, walk->vmemmap_pages);
 	set_pte_at(&init_mm, addr, pte, entry);
 }
@@ -331,6 +340,24 @@ int vmemmap_remap_free(unsigned long start, unsigned long end,
 		.reuse_addr	= reuse,
 		.vmemmap_pages	= &vmemmap_pages,
 	};
+	int nid = page_to_nid((struct page *)start);
+	gfp_t gfp_mask = GFP_KERNEL | __GFP_THISNODE | __GFP_NORETRY |
+			__GFP_NOWARN;
+
+	/*
+	 * Allocate a new head vmemmap page to avoid breaking a contiguous
+	 * block of struct page memory when freeing it back to page allocator
+	 * in free_vmemmap_page_list(). This will allow the likely contiguous
+	 * struct page backing memory to be kept contiguous and allowing for
+	 * more allocations of hugepages. Fallback to the currently
+	 * mapped head page in case should it fail to allocate.
+	 */
+	walk.reuse_page = alloc_pages_node(nid, gfp_mask, 0);
+	if (walk.reuse_page) {
+		copy_page(page_to_virt(walk.reuse_page),
+			  (void *)walk.reuse_addr);
+		list_add(&walk.reuse_page->lru, &vmemmap_pages);
+	}
 
 	/*
 	 * In order to make remapping routine most efficient for the huge pages,