Messages in this thread Patch in this message | | | Date | Tue, 21 Mar 2023 11:40:47 -0400 | From | Steven Rostedt <> | Subject | Re: [PATCH 1/2] ring-buffer: Introducing ring-buffer mapping functions |
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On Tue, 21 Mar 2023 15:17:15 +0000 Vincent Donnefort <vdonnefort@google.com> wrote:
> On Mon, Mar 20, 2023 at 09:45:16PM -0400, Steven Rostedt wrote: > > On Fri, 17 Mar 2023 14:33:09 +0000 > > Vincent Donnefort <vdonnefort@google.com> wrote: > > > > > Also, the meta-page being... a single page, this limits at the moment the > > > number of pages in the ring-buffer that can be mapped: ~3MB on a 4K pages > > > system. > > > > I hate this limitation, so I fixed it ;-) > > Thanks a lot for having a look. Do you mind if I fold this in my patch for a V2?
Hold off, I found some bugs that I'm fixing ;-)
> > > > > I added a meta_page_size field to the meta page, and user space can do: > > > > meta = mmap(NULL, page_size, PROT_READ, MAP_SHARED, fd, 0); > > if (meta == MAP_FAILED) > > pdie("mmap"); > > > > map = meta; > > meta_len = map->meta_page_size; > > > > if (meta_len > page_size) { > > munmap(meta, page_size); > > meta = mmap(NULL, meta_len, PROT_READ, MAP_SHARED, fd, 0); > > if (meta == MAP_FAILED) > > pdie("mmap"); > > map = meta; > > } > > > > This appears to work (but I'm still testing it). > > > > -- Steve > > > > diff --git a/include/uapi/linux/trace_mmap.h b/include/uapi/linux/trace_mmap.h > > index 24bcec754a35..12f3f7ee33d9 100644 > > --- a/include/uapi/linux/trace_mmap.h > > +++ b/include/uapi/linux/trace_mmap.h > > @@ -18,6 +18,7 @@ struct ring_buffer_meta_page { > > __u32 reader_page; > > __u32 nr_data_pages; /* doesn't take into account the reader_page */ > > __u32 data_page_head; /* index of data_pages[] */ > > + __u32 meta_page_size; /* size of the meta page */ > > Do we want a specific field here? That could be deduced from nr_data_pages() > quite easily?
I rather not have too much implementation detail knowledge in user space. It only removes a single entry, and it makes user space easier. In fact, I'm thinking we should not include "__u32 data_pages[]" but instead add a: "__u32 data_start" where user space does:
__u32 *data_pages = (_u32 *)meta_page + meta_page->data_start;
That way we could extend the data provided by the meta_page in the future.
-- Steve
> > > > __u32 data_pages[]; > > }; > > > > diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c > > index 10a17e78cfe6..77c92e4a7adc 100644 > > --- a/kernel/trace/ring_buffer.c > > +++ b/kernel/trace/ring_buffer.c > > @@ -526,6 +526,7 @@ struct ring_buffer_per_cpu { > > u64 read_stamp; > > > > int mapped; > > + int meta_order; > > struct mutex mapping_lock; > > unsigned long *page_ids; /* ID to addr */ > > struct ring_buffer_meta_page *meta_page; > > @@ -5898,7 +5899,7 @@ int ring_buffer_read_page(struct trace_buffer *buffer, > > EXPORT_SYMBOL_GPL(ring_buffer_read_page); > > > > #define META_PAGE_MAX_PAGES \ > > - ((PAGE_SIZE - (offsetof(struct ring_buffer_meta_page, data_page_head))) >> 2) > > + ((PAGE_SIZE - (offsetof(struct ring_buffer_meta_page, data_pages))) >> 2) > > > > [...]
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