Re: [PATCH 2/2] perf/ring_buffer: Fix high-order allocations for AUX space with correct MAX_ORDER limit

[Leo Yan]

On Mon, Jun 12, 2023 at 09:45:38AM +0100, James Clark wrote:

[...]

> > @@ -609,8 +609,8 @@ static struct page *rb_alloc_aux_page(int node, int order)
> >  {
> >  	struct page *page;
> >  
> > -	if (order > MAX_ORDER)
> > -		order = MAX_ORDER;
> > +	if (order >= MAX_ORDER)
> > +		order = MAX_ORDER - 1;
> >  
> >  	do {
> >  		page = alloc_pages_node(node, PERF_AUX_GFP, order);
> 
> 
> It seems like this was only just recently changed with this as the
> commit message (23baf83):
> 
>    mm, treewide: redefine MAX_ORDER sanely
> 
>   MAX_ORDER currently defined as number of orders page allocator
>   supports: user can ask buddy allocator for page order between 0 and
>   MAX_ORDER-1.
> 
>   This definition is counter-intuitive and lead to number of bugs all
>   over the kernel.
> 
>   Change the definition of MAX_ORDER to be inclusive: the range of
>   orders user can ask from buddy allocator is 0..MAX_ORDER now.
> 
> It might be worth referring to this in the commit message or adding a
> fixes: reference. Or maybe this new change isn't quite right?

Good point.  If so, we don't need this patch anymore.

Thanks for reminding, James.

Leo