From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail191.messagelabs.com (mail191.messagelabs.com [216.82.242.19]) by kanga.kvack.org (Postfix) with ESMTP id 3025E900086 for ; Mon, 18 Apr 2011 11:02:27 -0400 (EDT) Received: from d03relay04.boulder.ibm.com (d03relay04.boulder.ibm.com [9.17.195.106]) by e33.co.us.ibm.com (8.14.4/8.13.1) with ESMTP id p3IEtV2L003817 for ; Mon, 18 Apr 2011 08:55:31 -0600 Received: from d03av01.boulder.ibm.com (d03av01.boulder.ibm.com [9.17.195.167]) by d03relay04.boulder.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id p3IF2BBM123038 for ; Mon, 18 Apr 2011 09:02:12 -0600 Received: from d03av01.boulder.ibm.com (loopback [127.0.0.1]) by d03av01.boulder.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id p3IF2Aof032092 for ; Mon, 18 Apr 2011 09:02:10 -0600 Subject: Re: [RFC][PATCH 2/3] track numbers of pagetable pages From: Dave Hansen In-Reply-To: <20110416104456.3915b7de@mfleming-mobl1.ger.corp.intel.com> References: <20110415173821.62660715@kernel> <20110415173823.EA7A7473@kernel> <20110416104456.3915b7de@mfleming-mobl1.ger.corp.intel.com> Content-Type: text/plain; charset="ISO-8859-1" Date: Mon, 18 Apr 2011 08:02:04 -0700 Message-ID: <1303138924.9615.2487.camel@nimitz> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Matt Fleming Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org On Sat, 2011-04-16 at 10:44 +0100, Matt Fleming wrote: > > static inline void pgtable_page_dtor(struct mm_struct *mm, struct page *page) > > { > > pte_lock_deinit(page); > > + dec_mm_counter(mm, MM_PTEPAGES); > > dec_zone_page_state(page, NR_PAGETABLE); > > } > > I'm probably missing something really obvious but... > > Is this safe in the non-USE_SPLIT_PTLOCKS case? If we're not using > split-ptlocks then inc/dec_mm_counter() are only safe when done under > mm->page_table_lock, right? But it looks to me like we can end up doing, > > __pte_alloc() > pte_alloc_one() > pgtable_page_ctor() > > before acquiring mm->page_table_lock in __pte_alloc(). No, it's probably not safe. We'll have to come up with something a bit different in that case. Either that, or just kill the non-atomic case. Surely there's some percpu magic counter somewhere in the kernel that is optimized for fast (unlocked?) updates and rare, slow reads. -- Dave -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org