From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f42.google.com (mail-pa0-f42.google.com [209.85.220.42]) by kanga.kvack.org (Postfix) with ESMTP id A32C56B0005 for ; Tue, 26 Jan 2016 19:36:13 -0500 (EST) Received: by mail-pa0-f42.google.com with SMTP id ho8so105860347pac.2 for ; Tue, 26 Jan 2016 16:36:13 -0800 (PST) Received: from mail-pf0-x232.google.com (mail-pf0-x232.google.com. [2607:f8b0:400e:c00::232]) by mx.google.com with ESMTPS id l23si5257653pfi.182.2016.01.26.16.36.12 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 26 Jan 2016 16:36:12 -0800 (PST) Received: by mail-pf0-x232.google.com with SMTP id 65so19895970pfd.2 for ; Tue, 26 Jan 2016 16:36:12 -0800 (PST) Date: Tue, 26 Jan 2016 16:36:11 -0800 (PST) From: David Rientjes Subject: Re: [PATCH/RFC 3/3] s390: query dynamic DEBUG_PAGEALLOC setting In-Reply-To: <20160127001918.GA7089@js1304-P5Q-DELUXE> Message-ID: References: <1453799905-10941-1-git-send-email-borntraeger@de.ibm.com> <1453799905-10941-4-git-send-email-borntraeger@de.ibm.com> <20160126181903.GB4671@osiris> <20160127001918.GA7089@js1304-P5Q-DELUXE> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Joonsoo Kim Cc: Heiko Carstens , Christian Borntraeger , linux-kernel@vger.kernel.org, akpm@linux-foundation.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-s390@vger.kernel.org, x86@kernel.org On Wed, 27 Jan 2016, Joonsoo Kim wrote: > > I'd agree if CONFIG_DEBUG_PAGEALLOC only did anything when > > debug_pagealloc_enabled() is true, but that doesn't seem to be the case. > > When CONFIG_DEBUG_SLAB is enabled, for instance, CONFIG_DEBUG_PAGEALLOC > > also enables stackinfo storing and poisoning and it's not guarded by > > debug_pagealloc_enabled(). > > > > It seems like CONFIG_DEBUG_PAGEALLOC enables debugging functionality > > outside the scope of the debug_pagealloc=on kernel parameter, so > > DEBUG_PAGEALLOC(disabled) actually does mean something. > > Hello, David. > > I tried to fix CONFIG_DEBUG_SLAB case on 04/16 of following patchset. > > http://thread.gmane.org/gmane.linux.kernel.mm/144527 > > I found that there are more sites to fix but not so many. > We can do it. > For the slab case, sure, this can be fixed, but there is other code that uses CONFIG_DEBUG_PAGEALLOC to suggest debugging is always enabled and is indifferent to debug_pagealloc_enabled(). I find this in powerpc and sparc arch code as well as generic vmalloc code. If we can convert existing users that only check for CONFIG_DEBUG_PAGEALLOC to rather check for debug_pagealloc_enabled() and agree that it is only enabled for debug_pagealloc=on, then this would seem fine. However, I think we should at least consult with those users before removing an artifact from the kernel log that could be useful in debugging why a particular BUG() happened. -- 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