linux-kernel - [PATCH] mm/vmalloc.c: Remove always-true conditional in vmap_init_free

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Date:   Tue,  9 Jul 2019 01:06:31 +0800
From:   Pengfei Li <lpf.vector@...il.com>
To:     akpm@...ux-foundation.org
Cc:     urezki@...il.com, rpenyaev@...e.de, peterz@...radead.org,
        guro@...com, rick.p.edgecombe@...el.com, rppt@...ux.ibm.com,
        aryabinin@...tuozzo.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Pengfei Li <lpf.vector@...il.com>
Subject: [PATCH] mm/vmalloc.c: Remove always-true conditional in vmap_init_free_space

When unsigned long variables are subtracted from one another,
the result is always non-negative.

The vmap_area_list is sorted by address.

So the following two conditions are always true.

1) if (busy->va_start - vmap_start > 0)
2) if (vmap_end - vmap_start > 0)

Just remove them.

Signed-off-by: Pengfei Li <lpf.vector@...il.com>
---
 mm/vmalloc.c | 32 +++++++++++++-------------------
 1 file changed, 13 insertions(+), 19 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 0f76cca32a1c..c7bdbdc18472 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -1810,31 +1810,25 @@ static void vmap_init_free_space(void)
 	 *  |<--------------------------------->|
 	 */
 	list_for_each_entry(busy, &vmap_area_list, list) {
-		if (busy->va_start - vmap_start > 0) {
-			free = kmem_cache_zalloc(vmap_area_cachep, GFP_NOWAIT);
-			if (!WARN_ON_ONCE(!free)) {
-				free->va_start = vmap_start;
-				free->va_end = busy->va_start;
-
-				insert_vmap_area_augment(free, NULL,
-					&free_vmap_area_root,
-						&free_vmap_area_list);
-			}
-		}
-
-		vmap_start = busy->va_end;
-	}
-
-	if (vmap_end - vmap_start > 0) {
 		free = kmem_cache_zalloc(vmap_area_cachep, GFP_NOWAIT);
 		if (!WARN_ON_ONCE(!free)) {
 			free->va_start = vmap_start;
-			free->va_end = vmap_end;
+			free->va_end = busy->va_start;
 
 			insert_vmap_area_augment(free, NULL,
-				&free_vmap_area_root,
-					&free_vmap_area_list);
+				&free_vmap_area_root, &free_vmap_area_list);
 		}
+
+		vmap_start = busy->va_end;
+	}
+
+	free = kmem_cache_zalloc(vmap_area_cachep, GFP_NOWAIT);
+	if (!WARN_ON_ONCE(!free)) {
+		free->va_start = vmap_start;
+		free->va_end = vmap_end;
+
+		insert_vmap_area_augment(free, NULL,
+			&free_vmap_area_root, &free_vmap_area_list);
 	}
 }
 
-- 
2.21.0