[PATCH] mm, vmalloc: fix high order __GFP_NOFAIL allocations

[Michal Hocko]

Gao Xiang has reported that the page allocator complains about high
order __GFP_NOFAIL request coming from the vmalloc core:

 __alloc_pages+0x1cb/0x5b0 mm/page_alloc.c:5549
 alloc_pages+0x1aa/0x270 mm/mempolicy.c:2286
 vm_area_alloc_pages mm/vmalloc.c:2989 [inline]
 __vmalloc_area_node mm/vmalloc.c:3057 [inline]
 __vmalloc_node_range+0x978/0x13c0 mm/vmalloc.c:3227
 kvmalloc_node+0x156/0x1a0 mm/util.c:606
 kvmalloc include/linux/slab.h:737 [inline]
 kvmalloc_array include/linux/slab.h:755 [inline]
 kvcalloc include/linux/slab.h:760 [inline]

it seems that I have completely missed high order allocation backing
vmalloc areas case when implementing __GFP_NOFAIL support. This means
that [k]vmalloc at al. can allocate higher order allocations with
__GFP_NOFAIL which can trigger OOM killer for non-costly orders easily
or cause a lot of reclaim/compaction activity if those requests cannot
be satisfied.

Fix the issue by falling back to zero order allocations for __GFP_NOFAIL
requests if the high order request fails.

Fixes: 9376130c390a ("mm/vmalloc: add support for __GFP_NOFAIL")
Reported-by: Gao Xiang <hsiangkao@xxxxxxxxxxxxxxxxx>
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
---
 mm/vmalloc.c | 28 +++++++++++++++++++++++-----
 1 file changed, 23 insertions(+), 5 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index ef910bf349e1..bef6cf2b4d46 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2883,6 +2883,8 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
 		unsigned int order, unsigned int nr_pages, struct page **pages)
 {
 	unsigned int nr_allocated = 0;
+	gfp_t alloc_gfp = gfp;
+	bool nofail = false;
 	struct page *page;
 	int i;
 
@@ -2893,6 +2895,7 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
 	 * more permissive.
 	 */
 	if (!order) {
+		/* bulk allocator doesn't support nofail req. officially */
 		gfp_t bulk_gfp = gfp & ~__GFP_NOFAIL;
 
 		while (nr_allocated < nr_pages) {
@@ -2931,20 +2934,35 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
 			if (nr != nr_pages_request)
 				break;
 		}
+	} else if (gfp & __GFP_NOFAIL) {
+		/*
+		 * Higher order nofail allocations are really expensive and
+		 * potentially dangerous (pre-mature OOM, disruptive reclaim
+		 * and compaction etc.
+		 */
+		alloc_gfp &= ~__GFP_NOFAIL;
+		nofail = true;
 	}
 
 	/* High-order pages or fallback path if "bulk" fails. */
-
 	while (nr_allocated < nr_pages) {
 		if (fatal_signal_pending(current))
 			break;
 
 		if (nid == NUMA_NO_NODE)
-			page = alloc_pages(gfp, order);
+			page = alloc_pages(alloc_gfp, order);
 		else
-			page = alloc_pages_node(nid, gfp, order);
-		if (unlikely(!page))
-			break;
+			page = alloc_pages_node(nid, alloc_gfp, order);
+		if (unlikely(!page)) {
+			if (!nofail)
+				break;
+
+			/* fall back to the zero order allocations */
+			alloc_gfp |= __GFP_NOFAIL;
+			order = 0;
+			continue;
+		}
+
 		/*
 		 * Higher order allocations must be able to be treated as
 		 * indepdenent small pages by callers (as they can with
-- 
2.30.2

-- 
Michal Hocko
SUSE Labs