On Sat, 7 Oct 2023 21:51:01 +0800 Hou Tao <houtao@xxxxxxxxxxxxxxx> wrote:
> From: Hou Tao <houtao1@xxxxxxxxxx>
>
> Introduce alloc_size_percpu() to get the size of the dynamic per-cpu
> area. It will be used by bpf memory allocator in the following patches.
> BPF memory allocator maintains multiple per-cpu area caches for multiple
> area sizes and it needs the size of dynamic per-cpu area to select the
> corresponding cache when bpf program frees the dynamic per-cpu area.
>
> --- a/mm/percpu.c
> +++ b/mm/percpu.c
> @@ -2244,6 +2244,35 @@ static void pcpu_balance_workfn(struct work_struct *work)
> mutex_unlock(&pcpu_alloc_mutex);
> }
>
> +/**
> + * alloc_size_percpu - the size of the dynamic percpu area
> + * @ptr: pointer to the dynamic percpu area
> + *
> + * Return the size of the dynamic percpu area @ptr.
> + *
> + * RETURNS:
> + * The size of the dynamic percpu area.
> + *
> + * CONTEXT:
> + * Can be called from atomic context.
> + */
> +size_t alloc_size_percpu(void __percpu *ptr)
> +{
> + struct pcpu_chunk *chunk;
> + int bit_off, end;
It's minor, but I'd suggest unsigned long for both.
> + void *addr;
> +
> + if (!ptr)
> + return 0;
> +
> + addr = __pcpu_ptr_to_addr(ptr);
> + /* No pcpu_lock here: ptr has not been freed, so chunk is still alive */
> + chunk = pcpu_chunk_addr_search(addr);
> + bit_off = (addr - chunk->base_addr) / PCPU_MIN_ALLOC_SIZE;
void* - void* is a ptrdiff_t, which is long or int.
> + end = find_next_bit(chunk->bound_map, pcpu_chunk_map_bits(chunk), bit_off + 1);
find_next_bit takes an unsigned long
> + return (end - bit_off) * PCPU_MIN_ALLOC_SIZE;
And then we don't need to worry about signedness issues.
> +}
> +
