Re: [PATCH 2/3] percpu: add __GFP_NORETRY semantics to the percpu balancing path

From: Tejun Heo
Date: Thu Feb 15 2018 - 16:39:27 EST


Hello,

On Thu, Feb 15, 2018 at 10:08:15AM -0600, Dennis Zhou wrote:
> -static struct pcpu_chunk *pcpu_create_chunk(void)
> +static struct pcpu_chunk *pcpu_create_chunk(gfp_t gfp)
> {
> const int nr_pages = pcpu_group_sizes[0] >> PAGE_SHIFT;
> struct pcpu_chunk *chunk;
> struct page *pages;
> int i;
>
> - chunk = pcpu_alloc_chunk();
> + chunk = pcpu_alloc_chunk(gfp);
> if (!chunk)
> return NULL;
>
> - pages = alloc_pages(GFP_KERNEL, order_base_2(nr_pages));
> + pages = alloc_pages(gfp | GFP_KERNEL, order_base_2(nr_pages));

Is there a reason to set GFP_KERNEL in this function? I'd prefer
pushing this to the callers.

> diff --git a/mm/percpu-vm.c b/mm/percpu-vm.c
> index 9158e5a..ea9906a 100644
> --- a/mm/percpu-vm.c
> +++ b/mm/percpu-vm.c
> @@ -37,7 +37,7 @@ static struct page **pcpu_get_pages(void)
> lockdep_assert_held(&pcpu_alloc_mutex);
>
> if (!pages)
> - pages = pcpu_mem_zalloc(pages_size);
> + pages = pcpu_mem_zalloc(pages_size, 0);
^^^^
because this is confusing
> static int pcpu_alloc_pages(struct pcpu_chunk *chunk,
> - struct page **pages, int page_start, int page_end)
> + struct page **pages, int page_start, int page_end,
> + gfp_t gfp)
> {
> - const gfp_t gfp = GFP_KERNEL | __GFP_HIGHMEM;
> unsigned int cpu, tcpu;
> int i;
>
> + gfp |= GFP_KERNEL | __GFP_HIGHMEM;
^^
double space

So, setting __GFP_HIGHMEM unconditionally here makes sense because
it's indicating the types of pages we can use (we also accept high
pages); however, I'm not sure GFP_KERNEL makes sense. That's about
"how to allocate" and looks like it should be left to the caller.

Thanks.

--
tejun