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Subject[PATCH] 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
vm_remove_mappings()->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. Let's pass
a pointer to the vm_area instead of vm_struct to vm_remove_mappings(),
so it can pass it to __remove_vm_area() and avoid the redundant area
lookup.

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

Perf report before:
29.44% cat [kernel.kallsyms] [k] free_unref_page
11.88% cat [kernel.kallsyms] [k] find_vmap_area
9.28% cat [kernel.kallsyms] [k] __free_pages
7.44% cat [kernel.kallsyms] [k] __slab_free
7.28% cat [kernel.kallsyms] [k] vunmap_page_range
4.56% cat [kernel.kallsyms] [k] __vunmap
3.64% cat [kernel.kallsyms] [k] __purge_vmap_area_lazy
3.04% cat [kernel.kallsyms] [k] __free_vmap_area

Perf report after:
32.41% cat [kernel.kallsyms] [k] free_unref_page
7.79% cat [kernel.kallsyms] [k] find_vmap_area
7.40% cat [kernel.kallsyms] [k] __slab_free
7.31% cat [kernel.kallsyms] [k] vunmap_page_range
6.84% cat [kernel.kallsyms] [k] __free_pages
6.01% cat [kernel.kallsyms] [k] __vunmap
3.98% cat [kernel.kallsyms] [k] smp_call_function_single
3.81% cat [kernel.kallsyms] [k] __purge_vmap_area_lazy
2.77% cat [kernel.kallsyms] [k] __free_vmap_area

Signed-off-by: Roman Gushchin <guro@fb.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
---
mm/vmalloc.c | 52 +++++++++++++++++++++++++++++-----------------------
1 file changed, 29 insertions(+), 23 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index c42872ed82ac..8d4907865614 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2075,6 +2075,22 @@ 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;
+
+ 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
@@ -2087,26 +2103,14 @@ 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 inline void set_area_direct_map(const struct vm_struct *area,
@@ -2119,9 +2123,10 @@ static inline void set_area_direct_map(const struct vm_struct *area,
set_direct_map(area->pages[i]);
}

-/* Handle removing and resetting vm mappings related to the vm_struct. */
-static void vm_remove_mappings(struct vm_struct *area, int deallocate_pages)
+/* Handle removing and resetting vm mappings related to the va->vm vm_struct. */
+static void vm_remove_mappings(struct vmap_area *va, int deallocate_pages)
{
+ struct vm_struct *area = va->vm;
unsigned long addr = (unsigned long)area->addr;
unsigned long start = ULONG_MAX, end = 0;
int flush_reset = area->flags & VM_FLUSH_RESET_PERMS;
@@ -2138,7 +2143,7 @@ static void vm_remove_mappings(struct vm_struct *area, int deallocate_pages)
set_memory_rw(addr, area->nr_pages);
}

- remove_vm_area(area->addr);
+ __remove_vm_area(va);

/* If this is not VM_FLUSH_RESET_PERMS memory, no need for the below. */
if (!flush_reset)
@@ -2178,6 +2183,7 @@ static void vm_remove_mappings(struct vm_struct *area, int deallocate_pages)
static void __vunmap(const void *addr, int deallocate_pages)
{
struct vm_struct *area;
+ struct vmap_area *va;

if (!addr)
return;
@@ -2186,17 +2192,18 @@ 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));

- vm_remove_mappings(area, deallocate_pages);
+ vm_remove_mappings(va, deallocate_pages);

if (deallocate_pages) {
int i;
@@ -2212,7 +2219,6 @@ 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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