Paul Mackerras <paulus@xxxxxxxxxx> writes: > 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... This get done in a later patch where we rename PMD_SHIFT to H_PMD_SHIFT. [PATCH V2 15/29] powerpc/mm: Rename hash specific page table bits (_PAGE* -> H_PAGE*) > > 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? The patch actually got updated after feedback from Kirill Updated patch here. We still want to fail during build for ppc64. So there is a BUILD_BUG_ON also added http://article.gmane.org/gmane.linux.kernel/2148538 -aneesh -- 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>