From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail143.messagelabs.com (mail143.messagelabs.com [216.82.254.35]) by kanga.kvack.org (Postfix) with SMTP id AB8DA6B006A for ; Thu, 21 Jan 2010 00:24:42 -0500 (EST) Received: from m6.gw.fujitsu.co.jp ([10.0.50.76]) by fgwmail5.fujitsu.co.jp (Fujitsu Gateway) with ESMTP id o0L5OdnP008321 for (envelope-from kamezawa.hiroyu@jp.fujitsu.com); Thu, 21 Jan 2010 14:24:39 +0900 Received: from smail (m6 [127.0.0.1]) by outgoing.m6.gw.fujitsu.co.jp (Postfix) with ESMTP id 064BF45DE4F for ; Thu, 21 Jan 2010 14:24:39 +0900 (JST) Received: from s6.gw.fujitsu.co.jp (s6.gw.fujitsu.co.jp [10.0.50.96]) by m6.gw.fujitsu.co.jp (Postfix) with ESMTP id D5BB745DE4C for ; Thu, 21 Jan 2010 14:24:38 +0900 (JST) Received: from s6.gw.fujitsu.co.jp (localhost.localdomain [127.0.0.1]) by s6.gw.fujitsu.co.jp (Postfix) with ESMTP id BBF2C1DB8041 for ; Thu, 21 Jan 2010 14:24:38 +0900 (JST) Received: from ml14.s.css.fujitsu.com (ml14.s.css.fujitsu.com [10.249.87.104]) by s6.gw.fujitsu.co.jp (Postfix) with ESMTP id 55E9F1DB803A for ; Thu, 21 Jan 2010 14:24:35 +0900 (JST) Date: Thu, 21 Jan 2010 14:21:06 +0900 From: KAMEZAWA Hiroyuki Subject: Re: [PATCH 5/8] vmalloc: simplify vread()/vwrite() Message-Id: <20100121142106.c13c2bbf.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: <20100121050521.GB24236@localhost> References: <20100113135305.013124116@intel.com> <20100113135957.833222772@intel.com> <20100114124526.GB7518@laptop> <20100118133512.GC721@localhost> <20100118142359.GA14472@laptop> <20100119013303.GA12513@localhost> <20100119112343.04f4eff5.kamezawa.hiroyu@jp.fujitsu.com> <20100121050521.GB24236@localhost> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Wu Fengguang Cc: Nick Piggin , Andrew Morton , LKML , Tejun Heo , Ingo Molnar , Andi Kleen , Hugh Dickins , Christoph Lameter , Linux Memory Management List List-ID: On Thu, 21 Jan 2010 13:05:21 +0800 Wu Fengguang wrote: > On Mon, Jan 18, 2010 at 07:23:43PM -0700, KAMEZAWA Hiroyuki wrote: > > On Tue, 19 Jan 2010 09:33:03 +0800 > > Wu Fengguang wrote: > > > > The whole thing looks stupid though, apparently kmap is used to avoid "the > > > > lock". But the lock is already held. We should just use the vmap > > > > address. > > > > > > Yes. I wonder why Kame introduced kmap_atomic() in d0107eb07 -- given > > > that he at the same time fixed the order of removing vm_struct and > > > vmap in dd32c279983b. > > > > > Hmm...I must check my thinking again before answering.. > > > > vmalloc/vmap is constructed by 2 layer. > > - vmalloc layer....guarded by vmlist_lock. > > - vmap layer ....gurderd by purge_lock. etc. > > > > Now, let's see how vmalloc() works. It does job in 2 steps. > > vmalloc(): > > - allocate vmalloc area to the list under vmlist_lock. > > - map pages. > > vfree() > > - free vmalloc area from the list under vmlist_lock. > > - unmap pages under purge_lock. > > > > Now. vread(), vwrite() just take vmlist_lock, doesn't take purge_lock(). > > It walks page table and find pte entry, page, kmap and access it. > > > > Oh, yes. It seems it's safe without kmap. But My concern is percpu allocator. > > > > It uses get_vm_area() and controls mapped pages by themselves and > > map/unmap pages by with their own logic. vmalloc.c is just used for > > alloc/free virtual address. > > > > Now, vread()/vwrite() just holds vmlist_lock() and walk page table > > without no guarantee that the found page is stably mapped. So, I used kmap. > > > > If I miss something, I'm very sorry to add such kmap. > > Ah Thanks for explanation! > > I did some audit and find that > > - set_memory_uc(), set_memory_array_uc(), set_pages_uc(), > set_pages_array_uc() are called EFI code and various video drivers, > all of them don't touch HIGHMEM RAM > > - Kame: ioremap() won't allow remap of physical RAM > > So kmap_atomic() is safe. Let's just settle on this patch? > I recommend you to keep check on VM_IOREMAP. That was checked far before I started to see Linux. Some _unknown_ driver can call get_vm_area() and map arbitrary pages there. I'm sorry I coundn't track discussion correctly. Thanks, -Kame -- 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