From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f54.google.com (mail-pa0-f54.google.com [209.85.220.54]) by kanga.kvack.org (Postfix) with ESMTP id 414716B0005 for ; Tue, 2 Feb 2016 16:51:37 -0500 (EST) Received: by mail-pa0-f54.google.com with SMTP id yy13so932275pab.3 for ; Tue, 02 Feb 2016 13:51:37 -0800 (PST) Received: from mail-pf0-x231.google.com (mail-pf0-x231.google.com. [2607:f8b0:400e:c00::231]) by mx.google.com with ESMTPS id b70si4253224pfj.56.2016.02.02.13.51.36 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 02 Feb 2016 13:51:36 -0800 (PST) Received: by mail-pf0-x231.google.com with SMTP id w123so1092828pfb.0 for ; Tue, 02 Feb 2016 13:51:36 -0800 (PST) Date: Tue, 2 Feb 2016 13:51:34 -0800 (PST) From: David Rientjes 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> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: 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 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