On Fri, 18 May 2007, Nick Piggin wrote:

quoted text
> However we don't have to let those 8 bytes go to waste: we can use them
> to store the virtual address of the page, which kind of makes sense for
> 64-bit, because they can likely to use complicated memory models.

That is not a valid consideration anymore. There is virtual memmap update 
pending with the sparsemem folks that will simplify things.

quoted text
> Many batch operations on struct page are completely random, and as such, I
> think it is better if each struct page fits completely into a single
> cacheline even if it means being slightly larger.

Right. That would simplify the calculations.
 
quoted text
> Don't let this space go to waste though, we can use page->virtual in order
> to optimise page_address operations.

page->virtual is a benefit if the page is cache hot. Otherwise it may 
cause a useless lookup.

I wonder if there are other uses for the free space?

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