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Subject[PATCH v4 1/2] mm: refactor __vunmap() to avoid duplicated call to find_vm_area()
Date
__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@fb.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Matthew Wilcox <willy@infradead.org>
Acked-by: Vlastimil Babka <vbabka@suse.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
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