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SubjectRe: [RFC] bpf: change bpf syacall to use u64 temp variables
On Mon, Oct 19, 2015 at 03:10:46PM +0800, yalin wang wrote:
> This patch change map_lookup_elem() and map_update_elem() function
> to use u64 temp variable if the key_size or value_size is less than
> u64, we don't need use kmalloc() for these small variables.
>
> Signed-off-by: yalin wang <yalin.wang2010@gmail.com>
> ---
> kernel/bpf/syscall.c | 30 ++++++++++++++++++++----------
> 1 file changed, 20 insertions(+), 10 deletions(-)
>
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index f640e5f..c82d7bf 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -189,7 +189,8 @@ static int map_lookup_elem(union bpf_attr *attr)
> void __user *uvalue = u64_to_ptr(attr->value);
> int ufd = attr->map_fd;
> struct bpf_map *map;
> - void *key, *value, *ptr;
> + u64 key_buf, value_buf;
> + void *key = &key_buf, *value = &value_buf, *ptr;
> struct fd f;
> int err;
>
> @@ -202,7 +203,8 @@ static int map_lookup_elem(union bpf_attr *attr)
> return PTR_ERR(map);
>
> err = -ENOMEM;
> - key = kmalloc(map->key_size, GFP_USER);
> + if (map->key_size > sizeof(u64))
> + key = kmalloc(map->key_size, GFP_USER);

I think it's a good optimization for common case.
Performance numbers would be good to prove the point.
Thanks



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