From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f46.google.com (mail-wm0-f46.google.com [74.125.82.46]) by kanga.kvack.org (Postfix) with ESMTP id C78CC828DF for ; Mon, 25 Jan 2016 05:07:12 -0500 (EST) Received: by mail-wm0-f46.google.com with SMTP id n5so71202446wmn.0 for ; Mon, 25 Jan 2016 02:07:12 -0800 (PST) Received: from e06smtp07.uk.ibm.com (e06smtp07.uk.ibm.com. [195.75.94.103]) by mx.google.com with ESMTPS id e18si27461367wjn.112.2016.01.25.02.07.11 for (version=TLS1 cipher=AES128-SHA bits=128/128); Mon, 25 Jan 2016 02:07:11 -0800 (PST) Received: from localhost by e06smtp07.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 25 Jan 2016 10:07:11 -0000 Received: from b06cxnps4074.portsmouth.uk.ibm.com (d06relay11.portsmouth.uk.ibm.com [9.149.109.196]) by d06dlp01.portsmouth.uk.ibm.com (Postfix) with ESMTP id 944CA17D806B for ; Mon, 25 Jan 2016 10:07:13 +0000 (GMT) Received: from d06av07.portsmouth.uk.ibm.com (d06av07.portsmouth.uk.ibm.com [9.149.37.248]) by b06cxnps4074.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id u0PA75P6590200 for ; Mon, 25 Jan 2016 10:07:05 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 u0PA75KC032246 for ; Mon, 25 Jan 2016 05:07:05 -0500 Subject: Re: [PATCH] mm/debug_pagealloc: Ask users for default setting of debug_pagealloc References: <1453713588-119602-1-git-send-email-borntraeger@de.ibm.com> <20160125094132.GA4298@osiris> <56A5EECE.90607@de.ibm.com> <20160125100248.GB4298@osiris> From: Christian Borntraeger Message-ID: <56A5F3C8.4050202@de.ibm.com> Date: Mon, 25 Jan 2016 11:07:04 +0100 MIME-Version: 1.0 In-Reply-To: <20160125100248.GB4298@osiris> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Heiko Carstens Cc: linux-kernel@vger.kernel.org, peterz@infradead.org, akpm@linux-foundation.org, linux-mm@kvack.org, Joonsoo Kim On 01/25/2016 11:02 AM, Heiko Carstens wrote: > 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 ;) Ok, I will give it a try, and come back with a rewording or an s390 patch. -- 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