[PATCH 2/3] mm: separate memory allocation and actual work in alloc_vmap_area()

[Roman Gushchin <guroan@xxxxxxxxx>]

alloc_vmap_area() is allocating memory for the vmap_area, and
performing the actual lookup of the vm area and vmap_area
initialization.

This prevents us from using a pre-allocated memory for the map_area
structure, which can be used in some cases to minimize the number
of required memory allocations.

Let's keep the memory allocation part in alloc_vmap_area() and
separate everything else into init_vmap_area().

Signed-off-by: Roman Gushchin <guro@xxxxxx>
Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Reviewed-by: Matthew Wilcox <willy@xxxxxxxxxxxxx>
---
 mm/vmalloc.c | 50 +++++++++++++++++++++++++++++++++-----------------
 1 file changed, 33 insertions(+), 17 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 8f0179895fb5..f1f19d1105c4 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -395,16 +395,10 @@ static void purge_vmap_area_lazy(void);
 
 static BLOCKING_NOTIFIER_HEAD(vmap_notify_list);
 
-/*
- * Allocate a region of KVA of the specified size and alignment, within the
- * vstart and vend.
- */
-static struct vmap_area *alloc_vmap_area(unsigned long size,
-				unsigned long align,
-				unsigned long vstart, unsigned long vend,
-				int node, gfp_t gfp_mask)
+static int init_vmap_area(struct vmap_area *va, unsigned long size,
+			  unsigned long align, unsigned long vstart,
+			  unsigned long vend, int node, gfp_t gfp_mask)
 {
-	struct vmap_area *va;
 	struct rb_node *n;
 	unsigned long addr;
 	int purged = 0;
@@ -416,11 +410,6 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
 
 	might_sleep();
 
-	va = kmalloc_node(sizeof(struct vmap_area),
-			gfp_mask & GFP_RECLAIM_MASK, node);
-	if (unlikely(!va))
-		return ERR_PTR(-ENOMEM);
-
 	/*
 	 * Only scan the relevant parts containing pointers to other objects
 	 * to avoid false negatives.
@@ -516,7 +505,7 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
 	BUG_ON(va->va_start < vstart);
 	BUG_ON(va->va_end > vend);
 
-	return va;
+	return 0;
 
 overflow:
 	spin_unlock(&vmap_area_lock);
@@ -538,8 +527,35 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
 	if (!(gfp_mask & __GFP_NOWARN) && printk_ratelimit())
 		pr_warn("vmap allocation for size %lu failed: use vmalloc=<size> to increase size\n",
 			size);
-	kfree(va);
-	return ERR_PTR(-EBUSY);
+
+	return -EBUSY;
+}
+
+/*
+ * Allocate a region of KVA of the specified size and alignment, within the
+ * vstart and vend.
+ */
+static struct vmap_area *alloc_vmap_area(unsigned long size,
+					 unsigned long align,
+					 unsigned long vstart,
+					 unsigned long vend,
+					 int node, gfp_t gfp_mask)
+{
+	struct vmap_area *va;
+	int ret;
+
+	va = kmalloc_node(sizeof(struct vmap_area),
+			gfp_mask & GFP_RECLAIM_MASK, node);
+	if (unlikely(!va))
+		return ERR_PTR(-ENOMEM);
+
+	ret = init_vmap_area(va, size, align, vstart, vend, node, gfp_mask);
+	if (ret) {
+		kfree(va);
+		return ERR_PTR(ret);
+	}
+
+	return va;
 }
 
 int register_vmap_purge_notifier(struct notifier_block *nb)
-- 
2.20.1