Messages in this thread | | | Subject | Re: [PATCH V2] mm/page_alloc: Add alloc_contig_pages() | From | David Hildenbrand <> | Date | Thu, 17 Oct 2019 09:21:24 +0200 |
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On 17.10.19 09:11, Michal Hocko wrote: > On Thu 17-10-19 10:44:41, Anshuman Khandual wrote: > [...] >> Does this add-on documentation look okay ? Should we also mention about the >> possible reduction in chances of success during pfn block search for the >> non-power-of-two cases as the implicit alignment will probably turn out to >> be bigger than nr_pages itself ? >> >> * Requested nr_pages may or may not be power of two. The search for suitable >> * memory range in a zone happens in nr_pages aligned pfn blocks. But in case >> * when nr_pages is not power of two, an implicitly aligned pfn block search >> * will happen which in turn will impact allocated memory block's alignment. >> * In these cases, the size (i.e nr_pages) and the alignment of the allocated >> * memory will be different. This problem does not exist when nr_pages is power >> * of two where the size and the alignment of the allocated memory will always >> * be nr_pages. > > I dunno, it sounds more complicated than really necessary IMHO. Callers > shouldn't really be bothered by memory blocks and other really deep > implementation details.. Wouldn't be the below sufficient? > > The allocated memory is always aligned to a page boundary. If nr_pages > is a power of two then the alignement is guaranteed to be to the given
s/alignement/alignment/
and "the PFN is guaranteed to be aligned to nr_pages" (the address is aligned to nr_pages*PAGE_SIZE)
> nr_pages (e.g. 1GB request would be aligned to 1GB). >
I'd probably add "This function will miss allocation opportunities if nr_pages is not a power of two (and the implicit alignment is bogus)."
--
Thanks,
David / dhildenb
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