diff --git a/mm/percpu.c b/mm/percpu.c
index 503ccad..a84cf99 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -824,8 +824,8 @@
  * pcpu_setup_first_chunk - initialize the first percpu chunk
  * @get_page_fn: callback to fetch page pointer
  * @static_size: the size of static percpu area in bytes
- * @unit_size: unit size in bytes, must be multiple of PAGE_SIZE, 0 for auto
- * @dyn_size: free size for dynamic allocation in bytes, 0 for auto
+ * @unit_size: unit size in bytes, must be multiple of PAGE_SIZE, -1 for auto
+ * @dyn_size: free size for dynamic allocation in bytes, -1 for auto
  * @base_addr: mapped address, NULL for auto
  * @populate_pte_fn: callback to allocate pagetable, NULL if unnecessary
  *
@@ -842,13 +842,14 @@
  * indicates end of pages for the cpu.  Note that @get_page_fn() must
  * return the same number of pages for all cpus.
  *
- * @unit_size, if non-zero, determines unit size and must be aligned
- * to PAGE_SIZE and equal to or larger than @static_size + @dyn_size.
+ * @unit_size, if non-negative, specifies unit size and must be
+ * aligned to PAGE_SIZE and equal to or larger than @static_size +
+ * @dyn_size.
  *
- * @dyn_size determines the number of free bytes after the static
- * area in the first chunk.  If zero, whatever left is available.
- * Specifying non-zero value make percpu leave the area after
- * @static_size + @dyn_size alone.
+ * @dyn_size, if non-negative, limits the number of bytes available
+ * for dynamic allocation in the first chunk.  Specifying non-negative
+ * value make percpu leave alone the area beyond @static_size +
+ * @dyn_size.
  *
  * Non-null @base_addr means that the caller already allocated virtual
  * region for the first chunk and mapped it.  percpu must not mess
@@ -863,8 +864,9 @@
  * percpu access.
  */
 size_t __init pcpu_setup_first_chunk(pcpu_get_page_fn_t get_page_fn,
-				     size_t static_size, size_t unit_size,
-				     size_t dyn_size, void *base_addr,
+				     size_t static_size,
+				     ssize_t unit_size, ssize_t dyn_size,
+				     void *base_addr,
 				     pcpu_populate_pte_fn_t populate_pte_fn)
 {
 	static struct vm_struct first_vm;
@@ -877,13 +879,17 @@
 	/* santiy checks */
 	BUILD_BUG_ON(ARRAY_SIZE(smap) >= PCPU_DFL_MAP_ALLOC);
 	BUG_ON(!static_size);
-	BUG_ON(!unit_size && dyn_size);
-	BUG_ON(unit_size && unit_size < static_size + dyn_size);
-	BUG_ON(unit_size & ~PAGE_MASK);
-	BUG_ON(base_addr && !unit_size);
+	if (unit_size >= 0) {
+		BUG_ON(unit_size < static_size +
+				   (dyn_size >= 0 ? dyn_size : 0));
+		BUG_ON(unit_size & ~PAGE_MASK);
+	} else {
+		BUG_ON(dyn_size >= 0);
+		BUG_ON(base_addr);
+	}
 	BUG_ON(base_addr && populate_pte_fn);
 
-	if (unit_size)
+	if (unit_size >= 0)
 		pcpu_unit_pages = unit_size >> PAGE_SHIFT;
 	else
 		pcpu_unit_pages = max_t(int, PCPU_MIN_UNIT_SIZE >> PAGE_SHIFT,
@@ -894,6 +900,9 @@
 	pcpu_chunk_struct_size = sizeof(struct pcpu_chunk)
 		+ num_possible_cpus() * pcpu_unit_pages * sizeof(struct page *);
 
+	if (dyn_size < 0)
+		dyn_size = pcpu_unit_size - static_size;
+
 	/*
 	 * Allocate chunk slots.  The additional last slot is for
 	 * empty chunks.
@@ -909,12 +918,7 @@
 	schunk->vm = &first_vm;
 	schunk->map = smap;
 	schunk->map_alloc = ARRAY_SIZE(smap);
-
-	if (dyn_size)
-		schunk->free_size = dyn_size;
-	else
-		schunk->free_size = pcpu_unit_size - static_size;
-
+	schunk->free_size = dyn_size;
 	schunk->contig_hint = schunk->free_size;
 
 	schunk->map[schunk->map_used++] = -static_size;