On Tue, Aug 2, 2022 at 6:31 AM Yafang Shao <laoar.shao@xxxxxxxxx> wrote:
>
> 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.
>
In such case you might as well put pages = bpf_map_area_alloc(); part
into this function and return struct page ** as a result, so that
everything related to pages is handled as a single unit. And then
bpf_map_pages_free() will free not just each individual page, but also
struct page*[] array.
Also please call it something ringbuf specific, e.g.,
bpf_ringbuf_pages_{alloc,free}()?
>
> --
> Regards
> Yafang
