From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f51.google.com (mail-wm0-f51.google.com [74.125.82.51]) by kanga.kvack.org (Postfix) with ESMTP id EBB696B0005 for ; Mon, 25 Jan 2016 05:02:53 -0500 (EST) Received: by mail-wm0-f51.google.com with SMTP id n5so71002170wmn.0 for ; Mon, 25 Jan 2016 02:02:53 -0800 (PST) Received: from e06smtp14.uk.ibm.com (e06smtp14.uk.ibm.com. [195.75.94.110]) by mx.google.com with ESMTPS id mp1si27407739wjc.177.2016.01.25.02.02.52 for (version=TLS1 cipher=AES128-SHA bits=128/128); Mon, 25 Jan 2016 02:02:52 -0800 (PST) Received: from localhost by e06smtp14.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 25 Jan 2016 10:02:52 -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 7574D219005E for ; Mon, 25 Jan 2016 10:02:37 +0000 (GMT) Received: from d06av11.portsmouth.uk.ibm.com (d06av11.portsmouth.uk.ibm.com [9.149.37.252]) by b06cxnps3075.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id u0PA2ncL61538542 for ; Mon, 25 Jan 2016 10:02:49 GMT Received: from d06av11.portsmouth.uk.ibm.com (localhost [127.0.0.1]) by d06av11.portsmouth.uk.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id u0PA2nRP015675 for ; Mon, 25 Jan 2016 03:02:49 -0700 Date: Mon, 25 Jan 2016 11:02:48 +0100 From: Heiko Carstens Subject: Re: [PATCH] mm/debug_pagealloc: Ask users for default setting of debug_pagealloc Message-ID: <20160125100248.GB4298@osiris> References: <1453713588-119602-1-git-send-email-borntraeger@de.ibm.com> <20160125094132.GA4298@osiris> <56A5EECE.90607@de.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <56A5EECE.90607@de.ibm.com> Sender: owner-linux-mm@kvack.org List-ID: To: Christian Borntraeger Cc: linux-kernel@vger.kernel.org, peterz@infradead.org, akpm@linux-foundation.org, linux-mm@kvack.org, Joonsoo Kim On Mon, Jan 25, 2016 at 10:45:50AM +0100, Christian Borntraeger wrote: > >> + By default this option will be almost for free and can be activated > >> + in distribution kernels. The overhead and the debugging can be enabled > >> + by DEBUG_PAGEALLOC_ENABLE_DEFAULT or the debug_pagealloc command line > >> + parameter. > > > > Sorry, but it's not almost for free and should not be used by distribution > > kernels. If we have DEBUG_PAGEALLOC enabled, at least on s390 we will not > > make use of 2GB and 1MB pagetable entries for the identy mapping anymore. > > Instead we will only use 4K mappings. > > Hmmm, can we change these code areas to use debug_pagealloc_enabled? I guess > this evaluated too late? Yes, that should be possible. "debug_pagealloc" is an early_param, which will be evaluated before we call paging_init() (both in arch/s390/kernel/setup.c). So it looks like this can be trivially changed. (replace the ifdefs in arch/s390/mm/vmem.c with debug_pagealloc_enabled()). > > I assume this is true for all architectures since freeing pages can happen > > in any context and therefore we can't allocate memory in order to split > > page tables. > > > > So enabling this will cost memory and put more pressure on the TLB. > > So I will change the description and drop the "if unsure" statement. Well, given that we can change it like above... I don't care anymore ;) -- 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