Matthew Wilcox <willy@infradead.org> schrieb am Mi. 14. Apr. 2021 um 20:52:

> On Wed, Apr 14, 2021 at 05:24:42PM +0200, David Hildenbrand wrote:
> > On 13.04.21 21:46, Matthew Wilcox (Oracle) wrote:
> > > +#if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP)
> > >   #define nth_page(page,n) pfn_to_page(page_to_pfn((page)) + (n))
> > > +#else
> > > +#define nth_page(page,n) ((page) + (n))
> > > +#endif
> >
> > For sparsemem we could optimize within a single memory section. But not
> sure
> > if it's worth the trouble.
>
> Not only is it not worth the trouble, I suspect it's more expensive to
> test-and-branch than just unconditionally call pfn_to_page() and
> page_to_pfn().  That said, I haven't measured.


My thinking was that in most cases we might stay within the section such
that there are barely any actual branches.


>
> SPARSEMEM_VMEMMAP is default Y, and enabled by arm64, ia64, powerpc,
> riscv, s390, sparc and x86.  I mean ... do we care any more?


Also true.
-- 
Thanks,

David / dhildenb