Re: [PATCH 6/9] bpf: arraymap: introduce BPF_MAP_TYPE_ARRAY_PERCPU

On Mon, Jan 11, 2016 at 11:56:58PM +0800, Ming Lei wrote:

This patch introduces percpu array map so that expensive
atomic operations can be avoided in eBPF prog in case of
ARRAY map.

PERCPU MAP uses the percpu version of update/lookup element
helpers and callbacks to access element in the map, and
the previous update/lookup element helpers and callbacks
don't work at the same time.

Signed-off-by: Ming Lei <tom.leiming@gmail.com>

useful stuff!

+	if (percpu) {
+		if (alloc_percpu_array(array, attr->max_entries,
+				       attr->value_size)) {
+			kvfree(array);
+			return ERR_PTR(-ENOMEM);
+		}
+		array->map.pages = round_up(attr->max_entries *
+				attr->value_size * num_possible_cpus(),
+				PAGE_SIZE) >> PAGE_SHIFT;

I think it would be more accurate to add it to array_size instead of
doing page rounding here.

-	array->map.pages = round_up(array_size, PAGE_SIZE) >> PAGE_SHIFT;
+	array->map.pages += round_up(array_size, PAGE_SIZE) >> PAGE_SHIFT;

and this line wouldn't need to change...