[PATCH] mm/vmalloc: allocate small pages for area->pages

[Xu Yu <xuyu@linux.alibaba.com>]

The area->pages stores the struct pages allocated for vmalloc mappings.
The allocated memory can be hugepage if arch has HAVE_ARCH_HUGE_VMALLOC
set, while area->pages itself does not have to be hugepage backed.

Suppose that we want to vmalloc 1026M of memory, then area->pages is
2052K in size, which is large than PMD_SIZE when the pagesize is 4K.
Currently, 4096K will be allocated for area->pages, wherein 2044K is
wasted.

This introduces __vmalloc_node_no_huge, and makes area->pages backed by
small pages, because I think to allocate hugepage for area->pages is
unnecessary and vulnerable to abuse.

Signed-off-by: Xu Yu <xuyu@linux.alibaba.com>
---
 include/linux/vmalloc.h |  2 ++
 mm/vmalloc.c            | 15 ++++++++++++---
 2 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
index 6e022cc712e6..e93f39eb46a5 100644
--- a/include/linux/vmalloc.h
+++ b/include/linux/vmalloc.h
@@ -150,6 +150,8 @@ extern void *__vmalloc_node_range(unsigned long size, unsigned long align,
 			const void *caller) __alloc_size(1);
 void *__vmalloc_node(unsigned long size, unsigned long align, gfp_t gfp_mask,
 		int node, const void *caller) __alloc_size(1);
+void *__vmalloc_node_no_huge(unsigned long size, unsigned long align,
+		gfp_t gfp_mask, int node, const void *caller) __alloc_size(1);
 void *vmalloc_no_huge(unsigned long size) __alloc_size(1);
 
 extern void vfree(const void *addr);
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index d2a00ad4e1dd..0bdbb96d3e3f 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2925,17 +2925,18 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
 	unsigned long size = get_vm_area_size(area);
 	unsigned long array_size;
 	unsigned int nr_small_pages = size >> PAGE_SHIFT;
+	unsigned int max_small_pages = ALIGN(size, 1UL << page_shift) >> PAGE_SHIFT;
 	unsigned int page_order;
 
-	array_size = (unsigned long)nr_small_pages * sizeof(struct page *);
+	array_size = (unsigned long)max_small_pages * sizeof(struct page *);
 	gfp_mask |= __GFP_NOWARN;
 	if (!(gfp_mask & (GFP_DMA | GFP_DMA32)))
 		gfp_mask |= __GFP_HIGHMEM;
 
 	/* Please note that the recursion is strictly bounded. */
 	if (array_size > PAGE_SIZE) {
-		area->pages = __vmalloc_node(array_size, 1, nested_gfp, node,
-					area->caller);
+		area->pages = __vmalloc_node_no_huge(array_size, 1, nested_gfp,
+						     node, area->caller);
 	} else {
 		area->pages = kmalloc_node(array_size, nested_gfp, node);
 	}
@@ -3114,6 +3115,14 @@ void *__vmalloc_node(unsigned long size, unsigned long align,
 	return __vmalloc_node_range(size, align, VMALLOC_START, VMALLOC_END,
 				gfp_mask, PAGE_KERNEL, 0, node, caller);
 }
+
+void *__vmalloc_node_no_huge(unsigned long size, unsigned long align,
+			     gfp_t gfp_mask, int node, const void *caller)
+{
+	return __vmalloc_node_range(size, align, VMALLOC_START, VMALLOC_END,
+				gfp_mask, PAGE_KERNEL, VM_NO_HUGE_VMAP, node, caller);
+}
+
 /*
  * This is only for performance analysis of vmalloc and stress purpose.
  * It is required by vmalloc test module, therefore do not use it other
-- 
2.20.1.2432.ga663e714