From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christian Borntraeger Subject: Re: [PATCH/RFC 3/3] s390: query dynamic DEBUG_PAGEALLOC setting Date: Wed, 27 Jan 2016 13:47:41 +0100 Message-ID: <56A8BC6D.9080101@de.ibm.com> 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> <20160127005920.GB7089@js1304-P5Q-DELUXE> <56A8BB15.9070305@suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <56A8BB15.9070305@suse.cz> Sender: linux-kernel-owner@vger.kernel.org List-Archive: List-Post: To: Vlastimil Babka , Joonsoo Kim , David Rientjes Cc: Heiko Carstens , 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 List-ID: On 01/27/2016 01:41 PM, Vlastimil Babka wrote: > On 01/27/2016 01:59 AM, Joonsoo Kim wrote: >> On Tue, Jan 26, 2016 at 04:36:11PM -0800, David Rientjes wrote: >>> >>> 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. >> >> Yes, at least, non-architecture dependent code (vmalloc, SLAB, SLUB) should >> be changed first. If Christian doesn't mind, I will try to fix above 3 >> things. > > I think it might be worth also to convert debug_pagealloc_enabled() to be based > on static key, like I did for page_owner [1]. That should help make it possible > to have virtually no overhead when compiling kernel with CONFIG_DEBUG_PAGEALLOC > without enabling it boot-time. I assume it's one of the goals here? We could do something like that but dump_stack and setup of the initial identity mapping of the kernel as well as the initial page protection are not hot path as far as I can tell. Any other places? > > [1] http://www.spinics.net/lists/linux-mm/msg100795.html