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

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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




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