Hi Christoph, On Thu, Oct 04, 2012 at 06:17:37PM +0000, Christoph Lameter wrote: > On Thu, 4 Oct 2012, Andrea Arcangeli wrote: > > > So we could drop page_autonuma by creating a CONFIG_SLUB=y dependency > > (AUTONUMA wouldn't be available in the kernel config if SLAB=y, and it > > also wouldn't be available on 32bit archs but the latter isn't a > > problem). > > Nope it should depend on page struct alignment. Other kernel subsystems > may be depeding on page struct alignment in the future (and some other > arches may already have that requirement) But currently only SLUB x86 64bit selects CONFIG_HAVE_ALIGNED_STRUCT_PAGE: arch/Kconfig:config HAVE_ALIGNED_STRUCT_PAGE arch/x86/Kconfig: select HAVE_ALIGNED_STRUCT_PAGE if SLUB && !M386 include/linux/mm_types.h: defined(CONFIG_HAVE_ALIGNED_STRUCT_PAGE) include/linux/mm_types.h:#ifdef CONFIG_HAVE_ALIGNED_STRUCT_PAGE mm/slub.c: defined(CONFIG_HAVE_ALIGNED_STRUCT_PAGE) mm/slub.c: defined(CONFIG_HAVE_ALIGNED_STRUCT_PAGE) mm/slub.c: defined(CONFIG_HAVE_ALIGNED_STRUCT_PAGE) So in practice a dependency on CONFIG_HAVE_ALIGNED_STRUCT_PAGE would still mean the same: only available when SLUB enables it, and only on x86 64bit (ppc64?). If you mean CONFIG_AUTONUMA=y should select (not depend) on CONFIG_HAVE_ALIGNED_STRUCT_PAGE, that would allow to enable it in all .configs but it would have a worse cons: losing 8bytes per page unconditionally (even when booting on non-NUMA hardware). The current page_autonuma solution is substantially memory-cheaper than selecting CONFIG_HAVE_ALIGNED_STRUCT_PAGE: it allocates 2bytes per page at boot time but only if booting on real NUMA hardware (without altering the page structure). So to me it looks still quite a decent tradeoff. Thanks, Andrea -- 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>