From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail202.messagelabs.com (mail202.messagelabs.com [216.82.254.227]) by kanga.kvack.org (Postfix) with SMTP id 1516D9000C1 for ; Tue, 26 Apr 2011 10:57:48 -0400 (EDT) Date: Tue, 26 Apr 2011 15:57:43 +0100 From: Matt Fleming Subject: Re: [RFC][PATCH 2/3] track numbers of pagetable pages Message-ID: <20110426155743.2e76282d@mfleming-mobl1.ger.corp.intel.com> In-Reply-To: <1303138924.9615.2487.camel@nimitz> References: <20110415173821.62660715@kernel> <20110415173823.EA7A7473@kernel> <20110416104456.3915b7de@mfleming-mobl1.ger.corp.intel.com> <1303138924.9615.2487.camel@nimitz> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Dave Hansen Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Hugh Dickins [Added Hugh Dickins to the CC list] Sorry it's taken me so long to reply Dave. On Mon, 18 Apr 2011 08:02:04 -0700 Dave Hansen wrote: > 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. It seems it was Hugh that added these atomics in f412ac08c986 ("[PATCH] mm: fix rss and mmlist locking"). Hugh, what was the reason that you left the old counters around (the ones protected by page_table_lock)? It seems to me that we could delete those and just have the single case that uses the atomic_t operations. Would anyone object to a patch that removed the non-atomic case? -- Matt Fleming, Intel Open Source Technology Center -- 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