mm/vmalloc: improve allocation failure error messages

There are several reasons why a vmalloc can fail, virtual space exhausted,
page array allocation failure, page allocation failure, and kernel page
table allocation failure.

Add distinct warning messages for the main causes of failure, with some
added information like page order or allocation size where applicable.

[urezki@gmail.com: print correct vmalloc allocation size]
  Link: https://lkml.kernel.org/r/20210329193214.GA28602@pc638.lan

Link: https://lkml.kernel.org/r/20210322021806.892164-6-npiggin@gmail.comSigned-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/vmalloc.c

@@ -2790,6 +2790,10 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
 
 	if (!pages) {
 		free_vm_area(area);
+		warn_alloc(gfp_mask, NULL,
+			   "vmalloc size %lu allocation failure: "
+			   "page array size %lu allocation failed",
+			   nr_small_pages * PAGE_SIZE, array_size);
 		return NULL;
 	}
 
@@ -2814,6 +2818,10 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
 			/* Successfully allocated i pages, free them in __vfree() */
 			area->nr_pages = i;
 			atomic_long_add(area->nr_pages, &nr_vmalloc_pages);
+			warn_alloc(gfp_mask, NULL,
+				   "vmalloc size %lu allocation failure: "
+				   "page order %u allocation failed",
+				   area->nr_pages * PAGE_SIZE, page_order);
 			goto fail;
 		}
 
@@ -2825,15 +2833,17 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
 	}
 	atomic_long_add(area->nr_pages, &nr_vmalloc_pages);
 
-	if (vmap_pages_range(addr, addr + size, prot, pages, page_shift) < 0)
+	if (vmap_pages_range(addr, addr + size, prot, pages, page_shift) < 0) {
+		warn_alloc(gfp_mask, NULL,
+			   "vmalloc size %lu allocation failure: "
+			   "failed to map pages",
+			   area->nr_pages * PAGE_SIZE);
 		goto fail;
+	}
 
 	return area->addr;
 
 fail:
-	warn_alloc(gfp_mask, NULL,
-			  "vmalloc: allocation failure, allocated %ld of %ld bytes",
-			  (area->nr_pages*PAGE_SIZE), size);
 	__vfree(area->addr);
 	return NULL;
 }
@@ -2867,9 +2877,14 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align,
 	unsigned long real_align = align;
 	unsigned int shift = PAGE_SHIFT;
 
-	if (!size || (size >> PAGE_SHIFT) > totalram_pages()) {
-		area = NULL;
-		goto fail;
+	if (WARN_ON_ONCE(!size))
+		return NULL;
+
+	if ((size >> PAGE_SHIFT) > totalram_pages()) {
+		warn_alloc(gfp_mask, NULL,
+			   "vmalloc size %lu allocation failure: "
+			   "exceeds total pages", real_size);
+		return NULL;
 	}
 
 	if (vmap_allow_huge && !(vm_flags & VM_NO_HUGE_VMAP) &&
@@ -2897,8 +2912,12 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align,
 	size = PAGE_ALIGN(size);
 	area = __get_vm_area_node(size, align, VM_ALLOC | VM_UNINITIALIZED |
 				vm_flags, start, end, node, gfp_mask, caller);
-	if (!area)
+	if (!area) {
+		warn_alloc(gfp_mask, NULL,
+			   "vmalloc size %lu allocation failure: "
+			   "vm_struct allocation failed", real_size);
 		goto fail;
+	}
 
 	addr = __vmalloc_area_node(area, gfp_mask, prot, shift, node);
 	if (!addr)
@@ -2923,11 +2942,6 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align,
 		goto again;
 	}
 
-	if (!area) {
-		/* Warn for area allocation, page allocations already warn */
-		warn_alloc(gfp_mask, NULL,
-			  "vmalloc: allocation failure: %lu bytes", real_size);
-	}
 	return NULL;
 }