On Fri, Aug 07, 2026 at 04:25:33PM +0100, Vincent Donnefort wrote: > On Fri, Aug 07, 2026 at 10:45:26AM -0400, Steven Rostedt wrote: > > On Fri, 7 Aug 2026 10:43:12 +0100 > > Vincent Donnefort <[email protected]> wrote: > > > > > On Fri, Aug 07, 2026 at 09:14:26AM +0100, Vincent Donnefort wrote: > > > > On Fri, Aug 07, 2026 at 11:18:08AM +0900, Masami Hiramatsu wrote: > > > > > On Thu, 6 Aug 2026 22:13:01 +0100 > > > > > Vincent Donnefort <[email protected]> wrote: > > > > > > > > > > > Dynamically resizing a persistent ring buffer is not possible. > > > > > > Disable > > > > > > the feature. > > > > > > > > > > Is it true? Of course there is meaningless to resize the persistent > > > > > ring buffer (because it makes the buffer none-persistent), we are > > > > > currently > > > > > allows user to resize it (like for resizing unused persistent ring > > > > > buffer) > > > > > > > > __rb_allocate_pages() in ring_buffer_resize() would call for a > > > > persistent buffer > > > > rb_range_buffer(), which IIUC, is just reusing the same ring buffer > > > > pages as the > > > > one already in the persistent buffer. > > > > > > I have just tried and if reducing the size works, increasing fails in both > > > rb_set_head_page() and rb_insert_pages() with a warning, which I believe > > > is > > > expected. > > > > > > We could improve that, but it feels like it is a lot of work for a > > > meaningless > > > feature which we should just disable? > > > > Resizing a persistent ring buffer to a smaller size may be allowed, but I > > see no point in increasing the size. Making it smaller should allow us to > > give back a portion of the persistent ring buffer for general usage. > > > > -- Steve > > While I see the appeal to reclaim that memory, I don't think we have any good > interface for that. There is no nice way to get the list of pages that have > been > freed and we have no control over what part of the ring-buffer is removed. > > Also, as this memory is from a reserved-range, is there really a way to > re-inject > it into the buddy allocator?
free_reserved_page() would do actually. But then it is definitive. Happy to implement something like that. That also means that the instance can be actually freed? > > Perhaps what would make sense for resizing would be to support a CMA pool as a > persistent buffer? > > -- > Vincent -- Vincent
