On Wed, Feb 03, 2016 at 02:21:48PM +0100, Arnd Bergmann wrote: > I ran into build errors on ARM after Willy's newly added generic > TRANSPARENT_HUGEPAGE_PUD support. We don't support this feature > on ARM at all, but the patch causes a build error anyway: > > In file included from ../kernel/memremap.c:17:0: > ../include/linux/pfn_t.h:108:7: error: 'pud_mkdevmap' declared as function returning an array > pud_t pud_mkdevmap(pud_t pud); > > We don't use a PUD on ARM, so pud_t is defined as pmd_t, which > in turn is defined as > > typedef unsigned long pgd_t[2]; > > on NOMMU and on 2-level MMU configurations. There is an (unused) > other definition using a struct around the array, which happens to > work fine here. > > There is a comment in the file about the fact the other version > is "easier on the compiler", and I've traced that version back > to linux-2.1.80 when ARM support was first merged back in 1998. > > It's probably a safe assumption that this is no longer necessary: > The same logic existed in asm-i386 at the time but was removed > a year later in 2.3.23pre3. The STRICT_MM_TYPECHECKS logic > also ended up getting copied into these files: > > arch/alpha/include/asm/page.h > arch/arc/include/asm/page.h > arch/arm/include/asm/pgtable-3level-types.h > arch/arm64/include/asm/pgtable-types.h > arch/ia64/include/asm/page.h > arch/parisc/include/asm/page.h > arch/powerpc/include/asm/page.h > arch/sparc/include/asm/page_32.h > arch/sparc/include/asm/page_64.h For the sparc32 case we use the simpler variants. According to the comment this is due to limitation in the way we pass arguments in the sparc32 ABI. But I have not tried to compare a kernel for sparc32 with and without the use of structs. For sparc64 we use the stricter types (structs). I did not check other architectures - but just wanted to tell that the right choice may be architecture dependent. Sam -- 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>