On Fri, May 18, 2007 at 11:14:26AM -0700, Christoph Lameter wrote: > On Fri, 18 May 2007, Nick Piggin wrote: > > > 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. > > > 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.
It isn't the calculations I'm worried about, although they'll get simpler too. It is the cache cost. > > 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. It would be very rare for the page not to be in L1 cache at this point, because we've likely taken a reference on it and/or locked it or moved it between lists etc. > I wonder if there are other uses for the free space? Hugh points out that we should make _count and _mapcount atomic_long_t's, which would probably be a better use of the space once your vmemmap goes in. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/