On Tue, Aug 2, 2022 at 7:17 AM Andrii Nakryiko
<andrii.nakryiko@xxxxxxxxx> wrote:
>
> On Fri, Jul 29, 2022 at 8:23 AM Yafang Shao <laoar.shao@xxxxxxxxx> wrote:
> >
> > Introduce new helper bpf_map_pages_alloc() for this memory allocation.
> >
> > Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
> > ---
> > include/linux/bpf.h | 4 ++++
> > kernel/bpf/ringbuf.c | 27 +++++++++------------------
> > kernel/bpf/syscall.c | 41 +++++++++++++++++++++++++++++++++++++++++
> > 3 files changed, 54 insertions(+), 18 deletions(-)
> >
>
> [...]
>
> > /* Each data page is mapped twice to allow "virtual"
> > * continuous read of samples wrapping around the end of ring
> > @@ -95,16 +95,10 @@ static struct bpf_ringbuf *bpf_ringbuf_area_alloc(struct bpf_map *map,
> > if (!pages)
> > return NULL;
> >
> > - for (i = 0; i < nr_pages; i++) {
> > - page = alloc_pages_node(numa_node, flags, 0);
> > - if (!page) {
> > - nr_pages = i;
> > - goto err_free_pages;
> > - }
> > - pages[i] = page;
> > - if (i >= nr_meta_pages)
> > - pages[nr_data_pages + i] = page;
> > - }
> > + ptr = bpf_map_pages_alloc(map, pages, nr_meta_pages, nr_data_pages,
> > + numa_node, flags, 0);
> > + if (!ptr)
>
> bpf_map_pages_alloc() has some weird and confusing interface. It fills
> out pages (second argument) and also returns pages as void *. Why not
> just return int error (0 or -ENOMEM)? You are discarding this ptr
> anyways.
>
I will change it.
>
> But also thinking some more, bpf_map_pages_alloc() is very ringbuf
> specific (which other map will have exactly the same meaning for
> nr_meta_pages and nr_data_pages, where we also allocate 2 *
> nr_data_pages, etc).
>
> I don't think it makes sense to expose it as a generic internal API.
> Why not keep all that inside kernel/bpf/ringbuf.c instead?
>
Right, it is used in ringbuf.c only currently. I will keep it inside ringbuf.c.
--
Regards
Yafang
