On Mon, Feb 08, 2016 at 02:50:20PM +0530, Aneesh Kumar K.V wrote: > With next generation power processor, we are having a new mmu model > [1] that require us to maintain a different linux page table format. > > Inorder to support both current and future ppc64 systems with a single > kernel we need to make sure kernel can select between different page > table format at runtime. With the new MMU (radix MMU) added, we will > have two different pmd hugepage size 16MB for hash model and 2MB for > Radix model. Hence make HPAGE_PMD related values as a variable. But this patch doesn't actually turn any constant into a variable, as far as I can see... Most of what this patch does is to move two tests around: * The #if HPAGE_PMD_ORDER >= MAX_ORDER test get moved from a generic header into all archs except powerpc, and for powerpc it gets turned into BUILD_BUG_ON. However, BUILD_BUG_ON only works on things that are known at compile time, last time I looked. Doesn't it need to be a BUG_ON to prepare for HPAGE_PMD_ORDER being a variable that isn't known at compile time? * The existing BUILD_BUG_ON(HPAGE_PMD_ORDER < 2) gets turned into #if for all archs except powerpc, and for powerpc it stays as a BUILD_BUG_ON but gets moved to arch code. That doesn't really seem to accomplish anything. Once again, doesn't it need to become a BUG_ON? If so, could we just make it BUG_ON in the generic code where the BUILD_BUG_ON currently is? Paul. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>