From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753237AbcEWSW6 (ORCPT ); Mon, 23 May 2016 14:22:58 -0400 Received: from mail-wm0-f65.google.com ([74.125.82.65]:36357 "EHLO mail-wm0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752536AbcEWSW4 (ORCPT ); Mon, 23 May 2016 14:22:56 -0400 Date: Mon, 23 May 2016 20:22:53 +0200 From: Michal Hocko To: Yang Shi Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linaro-kernel@lists.linaro.org Subject: Re: [PATCH] mm: make CONFIG_DEFERRED_STRUCT_PAGE_INIT depends on !FLATMEM explicitly Message-ID: <20160523182252.GD32715@dhcp22.suse.cz> References: <1464022471-30545-1-git-send-email-yang.shi@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1464022471-30545-1-git-send-email-yang.shi@linaro.org> User-Agent: Mutt/1.6.0 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 23-05-16 09:54:31, Yang Shi wrote: > Per the suggestion from Michal Hocko [1], CONFIG_DEFERRED_STRUCT_PAGE_INIT > should be incompatible with FLATMEM, make this explicitly in Kconfig. I guess the changelog could benefit from some clarification. What do you think about the following: " DEFERRED_STRUCT_PAGE_INIT requires some ordering wrt other initialization operations, e.g. page_ext_init has to happen after the whole memmap is initialized properly. For SPARSEMEM this requires to wait for page_alloc_init_late. Other memory models (e.g. flatmem) might have different initialization layouts (page_ext_init_flatmem). Currently DEFERRED_STRUCT_PAGE_INIT depends on MEMORY_HOTPLUG which in turn depends on SPARSEMEM || X86_64_ACPI_NUMA depends on ARCH_ENABLE_MEMORY_HOTPLUG and X86_64_ACPI_NUMA depends on NUMA which in turn disable FLATMEM memory model: config ARCH_FLATMEM_ENABLE def_bool y depends on X86_32 && !NUMA so FLATMEM is ruled out via dependency maze. Be explicit and disable FLATMEM for DEFERRED_STRUCT_PAGE_INIT so that we do not reintroduce subtle initialization bugs " > > [1] http://lkml.kernel.org/r/20160523073157.GD2278@dhcp22.suse.cz > > Signed-off-by: Yang Shi > --- > mm/Kconfig | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/mm/Kconfig b/mm/Kconfig > index 2664c11..22fa818 100644 > --- a/mm/Kconfig > +++ b/mm/Kconfig > @@ -649,6 +649,7 @@ config DEFERRED_STRUCT_PAGE_INIT > default n > depends on ARCH_SUPPORTS_DEFERRED_STRUCT_PAGE_INIT > depends on MEMORY_HOTPLUG > + depends on !FLATMEM > help > Ordinarily all struct pages are initialised during early boot in a > single thread. On very large machines this can take a considerable > -- > 2.0.2 -- Michal Hocko SUSE Labs