From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from e06smtp11.uk.ibm.com (e06smtp11.uk.ibm.com [195.75.94.107]) (using TLSv1 with cipher CAMELLIA256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 7DC6E1A0204 for ; Wed, 3 Feb 2016 08:53:46 +1100 (AEDT) Received: from localhost by e06smtp11.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 2 Feb 2016 21:53:41 -0000 Received: from b06cxnps3075.portsmouth.uk.ibm.com (d06relay10.portsmouth.uk.ibm.com [9.149.109.195]) by d06dlp02.portsmouth.uk.ibm.com (Postfix) with ESMTP id 89D6D2190046 for ; Tue, 2 Feb 2016 21:53:25 +0000 (GMT) Received: from d06av07.portsmouth.uk.ibm.com (d06av07.portsmouth.uk.ibm.com [9.149.37.248]) by b06cxnps3075.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id u12LrccH4194814 for ; Tue, 2 Feb 2016 21:53:38 GMT Received: from d06av07.portsmouth.uk.ibm.com (localhost [127.0.0.1]) by d06av07.portsmouth.uk.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id u12Lrb4v020575 for ; Tue, 2 Feb 2016 16:53:38 -0500 Subject: Re: [PATCH v3 2/3] x86: query dynamic DEBUG_PAGEALLOC setting To: David Rientjes 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> 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 From: Christian Borntraeger Message-ID: <56B12560.4010201@de.ibm.com> Date: Tue, 2 Feb 2016 22:53:36 +0100 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252 List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On 02/02/2016 10:51 PM, David Rientjes wrote: > 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? > https://lkml.org/lkml/2016/1/29/266 ?