Re: [PATCH V2] mm/page_alloc: Add alloc_contig_pages()

[David Hildenbrand]

On 16.10.19 13:51, Michal Hocko wrote:
> On Wed 16-10-19 16:43:57, Anshuman Khandual wrote:
> > On 10/16/2019 04:39 PM, David Hildenbrand wrote:
> [...]
> > > Just to make sure, you ignored my comment regarding alignment
> > > although I explicitly mentioned it a second time? Thanks.
> >
> > I had asked Michal explicitly what to be included for the respin. Anyways
> > seems like the previous thread is active again. I am happy to incorporate
> > anything new getting agreed on there.
>
> Your patch is using the same alignment as the original code would do. If
> an explicit alignement is needed then this can be added on top, right?

Again, the "issue" I see here is that we could now pass in numbers that 
are not a power of two. For gigantic pages it was clear that we always 
have a number of two. The alignment does not make any sense otherwise.

What I'm asking for is

a) Document "The resulting PFN is aligned to nr_pages" and "nr_pages 
should be a power of two".

b) Eventually adding something like

if (WARN_ON_ONCE(!is_power_of_2(nr_pages)))
	return NULL;

Once we need other granularities we can think about the alignment and an 
optimized search-process.

--

Thanks,

David / dhildenb