From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f51.google.com (mail-pa0-f51.google.com [209.85.220.51]) by kanga.kvack.org (Postfix) with ESMTP id 0C9166B0032 for ; Thu, 7 May 2015 08:32:33 -0400 (EDT) Received: by pabtp1 with SMTP id tp1so39117059pab.2 for ; Thu, 07 May 2015 05:32:32 -0700 (PDT) Received: from bombadil.infradead.org (bombadil.infradead.org. [2001:1868:205::9]) by mx.google.com with ESMTPS id fo3si2650729pad.17.2015.05.07.05.32.32 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 07 May 2015 05:32:32 -0700 (PDT) Date: Thu, 7 May 2015 14:32:08 +0200 From: Peter Zijlstra Subject: Re: [PATCH RFC 01/15] uaccess: count pagefault_disable() levels in pagefault_disabled Message-ID: <20150507123208.GJ23123@twins.programming.kicks-ass.net> References: <1430934639-2131-1-git-send-email-dahi@linux.vnet.ibm.com> <1430934639-2131-2-git-send-email-dahi@linux.vnet.ibm.com> <20150507102254.GE23123@twins.programming.kicks-ass.net> <20150507125053.5d2e8f0a@thinkpad-w530> <20150507111231.GF23123@twins.programming.kicks-ass.net> <20150507134030.137deeb2@thinkpad-w530> <20150507115118.GT21418@twins.programming.kicks-ass.net> <20150507141439.160cb979@thinkpad-w530> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150507141439.160cb979@thinkpad-w530> Sender: owner-linux-mm@kvack.org List-ID: To: David Hildenbrand Cc: linux-kernel@vger.kernel.org, mingo@redhat.com, yang.shi@windriver.com, bigeasy@linutronix.de, benh@kernel.crashing.org, paulus@samba.org, akpm@linux-foundation.org, heiko.carstens@de.ibm.com, schwidefsky@de.ibm.com, borntraeger@de.ibm.com, mst@redhat.com, tglx@linutronix.de, David.Laight@ACULAB.COM, hughd@google.com, hocko@suse.cz, ralf@linux-mips.org, herbert@gondor.apana.org.au, linux@arm.linux.org.uk, airlied@linux.ie, daniel.vetter@intel.com, linux-mm@kvack.org, linux-arch@vger.kernel.org On Thu, May 07, 2015 at 02:14:39PM +0200, David Hildenbrand wrote: > Thanks :), well just to make sure I got your opinion on this correctly: > > 1. You think that 2 counters is the way to go for now ack > 2. You agree that we can't replace preempt_disable()+pagefault_disable() with > preempt_disable() (CONFIG_PREEMPT stuff), so we need to have them separately ack > 3. We need in_atomic() (in the fault handlers only!) in addition to make sure we > don't mess with irq contexts (In that case I would add a good comment to that > place, describing why preempt_disable() won't help) ack > I think this is the right way to go because: > > a) This way we don't have to modify preempt_disable() logic (including > PREEMPT_COUNT). > > b) There are not that many users relying on > preempt_disable()+pagefault_disable() (compared to pure preempt_disable() or > pagefault_disable() users), so the performance overhead of two cache lines > should be small. Users only making use of one of them should see no difference > in performance. indeed. > c) We correctly decouple preemption and pagefault logic. Therefore we can now > preempt when pagefaults are disabled, which feels right. Right, that's always been the intent of introducing pagefault_disable(). -- 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