linux-kernel - [PATCH v4 1/2] mm: refactor __vunmap() to avoid duplicated call to find_vm

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Date:   Wed, 17 Apr 2019 12:40:01 -0700
From:   Roman Gushchin <guroan@...il.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        kernel-team@...com, Matthew Wilcox <willy@...radead.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Vlastimil Babka <vbabka@...e.cz>, Roman Gushchin <guro@...com>
Subject: [PATCH v4 1/2] mm: refactor __vunmap() to avoid duplicated call to find_vm_area()

__vunmap() calls find_vm_area() twice without an obvious reason:
first directly to get the area pointer, second indirectly by calling
remove_vm_area(), which is again searching for the area.

To remove this redundancy, let's split remove_vm_area() into
__remove_vm_area(struct vmap_area *), which performs the actual area
removal, and remove_vm_area(const void *addr) wrapper, which can
be used everywhere, where it has been used before.

On my test setup, I've got 5-10% speed up on vfree()'ing 1000000
of 4-pages vmalloc blocks.

Perf report before:
  22.64%  cat      [kernel.vmlinux]  [k] free_pcppages_bulk
  10.30%  cat      [kernel.vmlinux]  [k] __vunmap
   9.80%  cat      [kernel.vmlinux]  [k] find_vmap_area
   8.11%  cat      [kernel.vmlinux]  [k] vunmap_page_range
   4.20%  cat      [kernel.vmlinux]  [k] __slab_free
   3.56%  cat      [kernel.vmlinux]  [k] __list_del_entry_valid
   3.46%  cat      [kernel.vmlinux]  [k] smp_call_function_many
   3.33%  cat      [kernel.vmlinux]  [k] kfree
   3.32%  cat      [kernel.vmlinux]  [k] free_unref_page

Perf report after:
  23.01%  cat      [kernel.kallsyms]  [k] free_pcppages_bulk
   9.46%  cat      [kernel.kallsyms]  [k] __vunmap
   9.15%  cat      [kernel.kallsyms]  [k] vunmap_page_range
   6.17%  cat      [kernel.kallsyms]  [k] __slab_free
   5.61%  cat      [kernel.kallsyms]  [k] kfree
   4.86%  cat      [kernel.kallsyms]  [k] bad_range
   4.67%  cat      [kernel.kallsyms]  [k] free_unref_page_commit
   4.24%  cat      [kernel.kallsyms]  [k] __list_del_entry_valid
   3.68%  cat      [kernel.kallsyms]  [k] free_unref_page
   3.65%  cat      [kernel.kallsyms]  [k] __list_add_valid
   3.19%  cat      [kernel.kallsyms]  [k] __purge_vmap_area_lazy
   3.10%  cat      [kernel.kallsyms]  [k] find_vmap_area
   3.05%  cat      [kernel.kallsyms]  [k] rcu_cblist_dequeue

Signed-off-by: Roman Gushchin <guro@...com>
Acked-by: Johannes Weiner <hannes@...xchg.org>
Reviewed-by: Matthew Wilcox <willy@...radead.org>
Acked-by: Vlastimil Babka <vbabka@...e.cz>
---
 mm/vmalloc.c | 47 +++++++++++++++++++++++++++--------------------
 1 file changed, 27 insertions(+), 20 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 92b784d8088c..8ad8e8464e55 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2068,6 +2068,24 @@ struct vm_struct *find_vm_area(const void *addr)
 	return NULL;
 }
 
+static struct vm_struct *__remove_vm_area(struct vmap_area *va)
+{
+	struct vm_struct *vm = va->vm;
+
+	might_sleep();
+
+	spin_lock(&vmap_area_lock);
+	va->vm = NULL;
+	va->flags &= ~VM_VM_AREA;
+	va->flags |= VM_LAZY_FREE;
+	spin_unlock(&vmap_area_lock);
+
+	kasan_free_shadow(vm);
+	free_unmap_vmap_area(va);
+
+	return vm;
+}
+
 /**
  * remove_vm_area - find and remove a continuous kernel virtual area
  * @addr:	    base address
@@ -2080,31 +2098,20 @@ struct vm_struct *find_vm_area(const void *addr)
  */
 struct vm_struct *remove_vm_area(const void *addr)
 {
+	struct vm_struct *vm = NULL;
 	struct vmap_area *va;
 
-	might_sleep();
-
 	va = find_vmap_area((unsigned long)addr);
-	if (va && va->flags & VM_VM_AREA) {
-		struct vm_struct *vm = va->vm;
-
-		spin_lock(&vmap_area_lock);
-		va->vm = NULL;
-		va->flags &= ~VM_VM_AREA;
-		va->flags |= VM_LAZY_FREE;
-		spin_unlock(&vmap_area_lock);
-
-		kasan_free_shadow(vm);
-		free_unmap_vmap_area(va);
+	if (va && va->flags & VM_VM_AREA)
+		vm = __remove_vm_area(va);
 
-		return vm;
-	}
-	return NULL;
+	return vm;
 }
 
 static void __vunmap(const void *addr, int deallocate_pages)
 {
 	struct vm_struct *area;
+	struct vmap_area *va;
 
 	if (!addr)
 		return;
@@ -2113,17 +2120,18 @@ static void __vunmap(const void *addr, int deallocate_pages)
 			addr))
 		return;
 
-	area = find_vm_area(addr);
-	if (unlikely(!area)) {
+	va = find_vmap_area((unsigned long)addr);
+	if (unlikely(!va || !(va->flags & VM_VM_AREA))) {
 		WARN(1, KERN_ERR "Trying to vfree() nonexistent vm area (%p)\n",
 				addr);
 		return;
 	}
 
+	area = va->vm;
 	debug_check_no_locks_freed(area->addr, get_vm_area_size(area));
 	debug_check_no_obj_freed(area->addr, get_vm_area_size(area));
 
-	remove_vm_area(addr);
+	__remove_vm_area(va);
 	if (deallocate_pages) {
 		int i;
 
@@ -2138,7 +2146,6 @@ static void __vunmap(const void *addr, int deallocate_pages)
 	}
 
 	kfree(area);
-	return;
 }
 
 static inline void __vfree_deferred(const void *addr)
-- 
2.20.1