From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753526Ab1DRPCc (ORCPT ); Mon, 18 Apr 2011 11:02:32 -0400 Received: from e34.co.us.ibm.com ([32.97.110.152]:57552 "EHLO e34.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752296Ab1DRPCY (ORCPT ); Mon, 18 Apr 2011 11:02:24 -0400 Subject: Re: [RFC][PATCH 2/3] track numbers of pagetable pages From: Dave Hansen To: Matt Fleming Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org 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 X-Mailer: Evolution 2.30.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.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