[PATCH] mm/vmalloc: Fallback to a single page allocator

["Uladzislau Rezki (Sony)" <urezki@gmail.com>]

Currently for order-0 pages we use a bulk-page allocator to get
set of pages. From the other hand not allocating all pages is
something that might occur. In that case we should fallbak to
the single-page allocator trying to get missing pages, because
it is more permissive(direct reclaim, etc).

Introduce a vm_area_alloc_pages() function where the described
logic is implemented.

Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
---
 mm/vmalloc.c | 81 +++++++++++++++++++++++++++++++++-------------------
 1 file changed, 52 insertions(+), 29 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index b2a0cbfa37c1..4d9c422124d3 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2756,6 +2756,54 @@ void *vmap_pfn(unsigned long *pfns, unsigned int count, pgprot_t prot)
 EXPORT_SYMBOL_GPL(vmap_pfn);
 #endif /* CONFIG_VMAP_PFN */
 
+static inline unsigned int
+vm_area_alloc_pages(gfp_t gfp, int nid, unsigned int page_order,
+	unsigned long nr_small_pages, struct page **pages)
+{
+	unsigned int nr_allocated = 0;
+
+	/*
+	 * For order-0 pages we make use of bulk allocator, if
+	 * the page array is partly or not at all populated due
+	 * to fails, fallback to a single page allocator that is
+	 * more permissive.
+	 */
+	if (!page_order)
+		nr_allocated = alloc_pages_bulk_array_node(
+			gfp, nid, nr_small_pages, pages);
+	else
+		/*
+		 * Compound pages required for remap_vmalloc_page if
+		 * high-order pages.
+		 */
+		gfp |= __GFP_COMP;
+
+	/* High-order pages or fallback path if "bulk" fails. */
+	while (nr_allocated < nr_small_pages) {
+		struct page *page;
+		int i;
+
+		page = alloc_pages_node(nid, gfp, page_order);
+		if (unlikely(!page))
+			break;
+
+		/*
+		 * Careful, we allocate and map page_order pages, but
+		 * tracking is done per PAGE_SIZE page so as to keep the
+		 * vm_struct APIs independent of the physical/mapped size.
+		 */
+		for (i = 0; i < (1U << page_order); i++)
+			pages[nr_allocated + i] = page + i;
+
+		if (gfpflags_allow_blocking(gfp))
+			cond_resched();
+
+		nr_allocated += 1U << page_order;
+	}
+
+	return nr_allocated;
+}
+
 static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
 				 pgprot_t prot, unsigned int page_shift,
 				 int node)
@@ -2789,37 +2837,11 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
 		return NULL;
 	}
 
-	area->nr_pages = 0;
 	set_vm_area_page_order(area, page_shift - PAGE_SHIFT);
 	page_order = vm_area_page_order(area);
 
-	if (!page_order) {
-		area->nr_pages = alloc_pages_bulk_array_node(
-			gfp_mask, node, nr_small_pages, area->pages);
-	} else {
-		/*
-		 * Careful, we allocate and map page_order pages, but tracking is done
-		 * per PAGE_SIZE page so as to keep the vm_struct APIs independent of
-		 * the physical/mapped size.
-		 */
-		while (area->nr_pages < nr_small_pages) {
-			struct page *page;
-			int i;
-
-			/* Compound pages required for remap_vmalloc_page */
-			page = alloc_pages_node(node, gfp_mask | __GFP_COMP, page_order);
-			if (unlikely(!page))
-				break;
-
-			for (i = 0; i < (1U << page_order); i++)
-				area->pages[area->nr_pages + i] = page + i;
-
-			if (gfpflags_allow_blocking(gfp_mask))
-				cond_resched();
-
-			area->nr_pages += 1U << page_order;
-		}
-	}
+	area->nr_pages = vm_area_alloc_pages(gfp_mask, node,
+		page_order, nr_small_pages, area->pages);
 
 	atomic_long_add(area->nr_pages, &nr_vmalloc_pages);
 
@@ -2835,7 +2857,8 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
 		goto fail;
 	}
 
-	if (vmap_pages_range(addr, addr + size, prot, area->pages, page_shift) < 0) {
+	if (vmap_pages_range(addr, addr + size, prot, area->pages,
+			page_shift) < 0) {
 		warn_alloc(gfp_mask, NULL,
 			   "vmalloc size %lu allocation failure: "
 			   "failed to map pages",
-- 
2.20.1