Re: [PATCH 1/6] ring-buffer: Prevent resizing of persistent ring buffer

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