From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755848AbcBBVvk (ORCPT ); Tue, 2 Feb 2016 16:51:40 -0500 Received: from mail-pf0-f174.google.com ([209.85.192.174]:36698 "EHLO mail-pf0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751720AbcBBVvh (ORCPT ); Tue, 2 Feb 2016 16:51:37 -0500 Date: Tue, 2 Feb 2016 13:51:34 -0800 (PST) From: David Rientjes X-X-Sender: rientjes@chino.kir.corp.google.com To: Christian Borntraeger cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-s390@vger.kernel.org, x86@kernel.org, linuxppc-dev@lists.ozlabs.org, davem@davemloft.net, Joonsoo Kim , davej@codemonkey.org.uk Subject: Re: [PATCH v3 2/3] x86: query dynamic DEBUG_PAGEALLOC setting In-Reply-To: Message-ID: References: <1453889401-43496-1-git-send-email-borntraeger@de.ibm.com> <1453889401-43496-3-git-send-email-borntraeger@de.ibm.com> <56A9E3D1.3090001@de.ibm.com> User-Agent: Alpine 2.10 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 28 Jan 2016, David Rientjes wrote: > On Thu, 28 Jan 2016, Christian Borntraeger wrote: > > > Indeed, I only touched the identity mapping and dump stack. > > The question is do we really want to change free_init_pages as well? > > The unmapping during runtime causes significant overhead, but the > > unmapping after init imposes almost no runtime overhead. Of course, > > things get fishy now as what is enabled and what not. > > > > Kconfig after my patch "mm/debug_pagealloc: Ask users for default setting of debug_pagealloc" > > (in mm) now states > > ----snip---- > > By default this option will have a small overhead, e.g. by not > > allowing the kernel mapping to be backed by large pages on some > > architectures. Even bigger overhead comes when the debugging is > > enabled by DEBUG_PAGEALLOC_ENABLE_DEFAULT or the debug_pagealloc > > command line parameter. > > ----snip---- > > > > So I am tempted to NOT change free_init_pages, but the x86 maintainers > > can certainly decide differently. Ingo, Thomas, H. Peter, please advise. > > > > I'm sorry, but I thought the discussion of the previous version of the > patchset led to deciding that all CONFIG_DEBUG_PAGEALLOC behavior would be > controlled by being enabled on the commandline and checked with > debug_pagealloc_enabled(). > > I don't think we should have a CONFIG_DEBUG_PAGEALLOC that does some stuff > and then a commandline parameter or CONFIG_DEBUG_PAGEALLOC_ENABLE_DEFAULT > to enable more stuff. It should either be all enabled by the commandline > (or config option) or split into a separate entity. > CONFIG_DEBUG_PAGEALLOC_LIGHT and CONFIG_DEBUG_PAGEALLOC would be fine, but > the current state is very confusing about what is being done and what > isn't. > Ping? From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Rientjes Subject: Re: [PATCH v3 2/3] x86: query dynamic DEBUG_PAGEALLOC setting Date: Tue, 2 Feb 2016 13:51:34 -0800 (PST) Message-ID: References: <1453889401-43496-1-git-send-email-borntraeger@de.ibm.com> <1453889401-43496-3-git-send-email-borntraeger@de.ibm.com> <56A9E3D1.3090001@de.ibm.com> Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Return-path: In-Reply-To: Sender: owner-linux-mm@kvack.org List-Archive: List-Post: To: Christian Borntraeger Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-s390@vger.kernel.org, x86@kernel.org, linuxppc-dev@lists.ozlabs.org, davem@davemloft.net, Joonsoo Kim , davej@codemonkey.org.uk List-ID: On Thu, 28 Jan 2016, David Rientjes wrote: > On Thu, 28 Jan 2016, Christian Borntraeger wrote: > > > Indeed, I only touched the identity mapping and dump stack. > > The question is do we really want to change free_init_pages as well? > > The unmapping during runtime causes significant overhead, but the > > unmapping after init imposes almost no runtime overhead. Of course, > > things get fishy now as what is enabled and what not. > > > > Kconfig after my patch "mm/debug_pagealloc: Ask users for default setting of debug_pagealloc" > > (in mm) now states > > ----snip---- > > By default this option will have a small overhead, e.g. by not > > allowing the kernel mapping to be backed by large pages on some > > architectures. Even bigger overhead comes when the debugging is > > enabled by DEBUG_PAGEALLOC_ENABLE_DEFAULT or the debug_pagealloc > > command line parameter. > > ----snip---- > > > > So I am tempted to NOT change free_init_pages, but the x86 maintainers > > can certainly decide differently. Ingo, Thomas, H. Peter, please advise. > > > > I'm sorry, but I thought the discussion of the previous version of the > patchset led to deciding that all CONFIG_DEBUG_PAGEALLOC behavior would be > controlled by being enabled on the commandline and checked with > debug_pagealloc_enabled(). > > I don't think we should have a CONFIG_DEBUG_PAGEALLOC that does some stuff > and then a commandline parameter or CONFIG_DEBUG_PAGEALLOC_ENABLE_DEFAULT > to enable more stuff. It should either be all enabled by the commandline > (or config option) or split into a separate entity. > CONFIG_DEBUG_PAGEALLOC_LIGHT and CONFIG_DEBUG_PAGEALLOC would be fine, but > the current state is very confusing about what is being done and what > isn't. > Ping? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org