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SubjectRe: [PATCH] mm: refactor __vunmap() to avoid duplicated call to find_vm_area()
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On 05/15/2019 05:21 AM, Roman Gushchin wrote:
> __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();

Is not this necessary any more ?

> -
> 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;
> }

Other callers of remove_vm_area() cannot use __remove_vm_area() directly as well
to save a look up ?

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