mm/vmalloc: modify struct vmap_area to reduce its size

Objective --------- The current implementation of struct vmap_area wasted space. After applying this commit, sizeof(struct vmap_area) has been reduced from 11 words to 8 words. Description ----------- 1) Pack "subtree_max_size", "vm" and "purge_list". This is no problem because A) "subtree_max_size" is only used when vmap_area is in "free" tree B) "vm" is only used when vmap_area is in "busy" tree C) "purge_list" is only used when vmap_area is in vmap_purge_list 2) Eliminate "flags". ;Since only one flag VM_VM_AREA is being used, and the same thing can be done by judging whether "vm" is NULL, then the "flags" can be eliminated.

Pengfei Li committed 7 years ago

Commit 688fcbf1 parent dd3b8352 files · +23 −21Browse files

Unified · Split

2 files

include/linux/vmalloc.h +13 −7
mm/vmalloc.c +10 −14

include/linux/vmalloc.h+13−7

@@ -53,15 +53,21 @@ struct vmap_area { · 52 unmodified lines
53	unsigned long va_start;	53	unsigned long va_start;
54	unsigned long va_end;	54	unsigned long va_end;
55		55
56	/*
57	* Largest available free size in subtree.
58	*/
59	unsigned long subtree_max_size;
60	unsigned long flags;
61	struct rb_node rb_node; /* address sorted rbtree */	56	struct rb_node rb_node; /* address sorted rbtree */
62	struct list_head list; /* address sorted list */	57	struct list_head list; /* address sorted list */
63	struct llist_node purge_list; /* "lazy purge" list */	58
64	struct vm_struct *vm;	59	/*
		60	* The following three variables can be packed, because
		61	* a vmap_area object is always one of the three states:
		62	* 1) in "free" tree (root is vmap_area_root)
		63	* 2) in "busy" tree (root is free_vmap_area_root)
		64	* 3) in purge list (head is vmap_purge_list)
		65	*/
		66	union {
		67	unsigned long subtree_max_size; /* in "free" tree */
		68	struct vm_struct vm; / in "busy" tree */
		69	struct llist_node purge_list; /* in purge list */
		70	};
65	};	71	};
66		72
67	/*	73	/*

mm/vmalloc.c+10−14

 #define DEBUG_AUGMENT_PROPAGATE_CHECK 0
 #define DEBUG_AUGMENT_LOWEST_MATCH_CHECK 0
-#define VM_VM_AREA	0x04
 static DEFINE_SPINLOCK(vmap_area_lock);
 /* Export for kexec only */
 	va->va_start = addr;
 	va->va_end = addr + size;
-	va->flags = 0;
+	va->vm = NULL;
 	insert_vmap_area(va, &vmap_area_root, &vmap_area_list);
 	spin_unlock(&vmap_area_lock);
 		if (WARN_ON_ONCE(!va))
 			continue;
-		va->flags = VM_VM_AREA;
 		va->va_start = (unsigned long)tmp->addr;
 		va->va_end = va->va_start + tmp->size;
 		va->vm = tmp;
 	vm->size = va->va_end - va->va_start;
 	vm->caller = caller;
 	va->vm = vm;
-	va->flags |= VM_VM_AREA;
 	spin_unlock(&vmap_area_lock);
 }
 	struct vmap_area *va;
 	va = find_vmap_area((unsigned long)addr);
-	if (va && va->flags & VM_VM_AREA)
+	if (!va)
-		return va->vm;
+		return NULL;
-	return NULL;
+	return va->vm;
 }
 /**
 	spin_lock(&vmap_area_lock);
 	va = __find_vmap_area((unsigned long)addr);
-	if (va && va->flags & VM_VM_AREA) {
+	if (va && va->vm) {
 		struct vm_struct *vm = va->vm;
 		va->vm = NULL;
-		va->flags &= ~VM_VM_AREA;
 		spin_unlock(&vmap_area_lock);
 		kasan_free_shadow(vm);
 		if (!count)
 			break;
-		if (!(va->flags & VM_VM_AREA))
+		if (!va->vm)
 			continue;
 		vm = va->vm;
 		if (!count)
 			break;
-		if (!(va->flags & VM_VM_AREA))
+		if (!va->vm)
 			continue;
 		vm = va->vm;
 	va = list_entry(p, struct vmap_area, list);
 	/*
-	 * s_show can encounter race with remove_vm_area, !VM_VM_AREA on
+	 * s_show can encounter race with remove_vm_area, !vm on behalf
-	 * behalf of vmap area is being tear down or vm_map_ram allocation.
+	 * of vmap area is being tear down or vm_map_ram allocation.
 	 */
-	if (!(va->flags & VM_VM_AREA)) {
+	if (!va->vm) {
 		seq_printf(m, "0x%pK-0x%pK %7ld vm_map_ram\n",
 			(void *)va->va_start, (void *)va->va_end,
 			va->va_end - va->va_start);

mm/vmalloc: modify struct vmap_area to reduce its size

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