On Tue, Mar 12, 2013 at 11:27:10AM +0100, Peter Zijlstra wrote:
> On Tue, 2013-03-12 at 11:05 +0100, Jiri Olsa wrote:
> > +/*
> > + * Returns the total number of pages allocated
> > + * by ring buffer including the user page.
> > + */
> > +static int page_nr(struct ring_buffer *rb)
> > +{
> > + return page_order(rb) == -1 ?
> > + 1 : /* no data, just user page */
> > + 1 + (1 << page_order(rb)); /* user page + data pages */
> > +}
>
> > @@ -371,9 +381,24 @@ struct ring_buffer *rb_alloc(int nr_pages, long
> > watermark, int cpu, int flags)
> > goto fail_all_buf;
> >
> > rb->user_page = all_buf;
> > - rb->data_pages[0] = all_buf + PAGE_SIZE;
> > - rb->page_order = ilog2(nr_pages);
> > - rb->nr_pages = 1;
>
> > +
> > + rb->data_pages[0] = nr_pages ? all_buf + PAGE_SIZE : NULL;
> > + rb->nr_pages = nr_pages ? 1 : 0;
> > + rb->page_order = ilog2(nr_pages);
> >
> > ring_buffer_init(rb, watermark, flags);
>
> Still somewhat confused by this.. wouldn't something 'simple' like the
> below suffice?
>
> Note how the !vmalloc branch also sets rb->nr_pages = nr_pages.
yep it would ;-) though I find it little confusing for:
>
> ---
> kernel/events/ring_buffer.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
> index 23cb34f..4f48d02 100644
> --- a/kernel/events/ring_buffer.c
> +++ b/kernel/events/ring_buffer.c
> @@ -316,7 +316,7 @@ void rb_free(struct ring_buffer *rb)
> struct page *
> perf_mmap_to_page(struct ring_buffer *rb, unsigned long pgoff)
> {
> - if (pgoff > (1UL << page_order(rb)))
> + if (pgoff > rb->nr_pages)
> return NULL;
here it's the '>' that masks that there's actually (rb->nr_pages + 1) pages
>
> return vmalloc_to_page((void *)rb->user_page + pgoff * PAGE_SIZE);
> @@ -336,7 +336,7 @@ static void rb_free_work(struct work_struct *work)
> int i, nr;
>
> rb = container_of(work, struct ring_buffer, work);
> - nr = 1 << page_order(rb);
> + nr = rb->nr_pages;
>
> base = rb->user_page;
> for (i = 0; i < nr + 1; i++)
and here's the user plus one
> @@ -373,7 +373,7 @@ struct ring_buffer *rb_alloc(int nr_pages, long
> watermark, int cpu, int flags)
> rb->user_page = all_buf;
> rb->data_pages[0] = all_buf + PAGE_SIZE;
> rb->page_order = ilog2(nr_pages);
> - rb->nr_pages = 1;
> + rb->nr_pages = nr_pages;
>
> ring_buffer_init(rb, watermark, flags);
but I'll get used to it np.. ;)
jirka
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