On Tue, 8 Sep 2009, Nick Piggin wrote: > On Mon, Sep 07, 2009 at 10:39:34PM +0100, Hugh Dickins wrote: > > KAMEZAWA Hiroyuki has observed customers of earlier kernels taking > > advantage of the ZERO_PAGE: which we stopped do_anonymous_page() from > > using in 2.6.24. And there were a couple of regression reports on LKML. > > > > Following suggestions from Linus, reinstate do_anonymous_page() use of > > the ZERO_PAGE; but this time avoid dirtying its struct page cacheline > > with (map)count updates - let vm_normal_page() regard it as abnormal. > > > > Use it only on arches which __HAVE_ARCH_PTE_SPECIAL (x86, s390, sh32, > > most powerpc): that's not essential, but minimizes additional branches > > (keeping them in the unlikely pte_special case); and incidentally > > excludes mips (some models of which needed eight colours of ZERO_PAGE > > to avoid costly exceptions). > > Without looking closely, why is it a big problem to have a > !HAVE PTE SPECIAL case? Couldn't it just be a check for > pfn == zero_pfn that is conditionally compiled away for pte > special architectures anyway? Yes, I'm uncomfortable with that restriction too: it makes for neater looking code in a couple of places, but it's not so good for the architectures to diverge gratuitously there. I'll give it a try without that restriction, see how it looks: it was Linus who proposed the "special" approach, I'm sure he'll speak up if he doesn't like how the alternative comes out. Tucking the test away in an asm-generic macro, we can leave the pain of a rangetest to the one mips case. By the way, in compiling that list of "special" architectures, I was surprised not to find ia64 amongst them. Not that it matters to me, but I thought the Fujitsu guys were usually keen on Itanium - do they realize that the special test is excluding it, or do they have their own special patch for it? > > If zero page is such a good idea, I don't see the logic of > limiting it like thisa. Your patch looks pretty clean though. > > At any rate, I think it might be an idea to cc linux-arch. Yes, thanks. Hugh -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
