From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753993Ab0DTIcQ (ORCPT ); Tue, 20 Apr 2010 04:32:16 -0400 Received: from mail-yw0-f194.google.com ([209.85.211.194]:36801 "EHLO mail-yw0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753474Ab0DTIcO convert rfc822-to-8bit (ORCPT ); Tue, 20 Apr 2010 04:32:14 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=g3EebyYUQl7yNmbwvn1uQyp6wnAeZDozegA82KBQdlSlbl+f8biOTs71ynatIBrjHQ BIhgvRRih7nk6ii7YvsZl64uGgbBc/4MRL+QhIopmUZ3WZUla4zF5klNYxvtZFOxBx2c VtmrK+YJL9IPZk0a5igXAoOE+7NsHM3m4w/R4= MIME-Version: 1.0 In-Reply-To: <20100420082057.GC19264@csn.ul.ie> References: <201004152210.o3FMA7KV001909@imap1.linux-foundation.org> <20100419190133.50a13021.kamezawa.hiroyu@jp.fujitsu.com> <20100419181442.GA19264@csn.ul.ie> <20100419193919.GB19264@csn.ul.ie> <20100420082057.GC19264@csn.ul.ie> Date: Tue, 20 Apr 2010 17:32:13 +0900 Message-ID: Subject: Re: error at compaction (Re: mmotm 2010-04-15-14-42 uploaded From: Minchan Kim To: Mel Gorman Cc: KAMEZAWA Hiroyuki , linux-kernel@vger.kernel.org, akpm@linux-foundation.org, "linux-mm@kvack.org" , "kosaki.motohiro@jp.fujitsu.com" Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 20, 2010 at 5:20 PM, Mel Gorman wrote: > On Tue, Apr 20, 2010 at 11:39:46AM +0900, Minchan Kim wrote: >> On Tue, Apr 20, 2010 at 4:39 AM, Mel Gorman wrote: >> > On Mon, Apr 19, 2010 at 07:14:42PM +0100, Mel Gorman wrote: >> >> On Mon, Apr 19, 2010 at 07:01:33PM +0900, KAMEZAWA Hiroyuki wrote: >> >> > >> >> > mmotm 2010-04-15-14-42 >> >> > >> >> > When I tried >> >> >  # echo 0 > /proc/sys/vm/compaction >> >> > >> >> > I see following. >> >> > >> >> > My enviroment was >> >> >   2.6.34-rc4-mm1+ (2010-04-15-14-42) (x86-64) CPUx8 >> >> >   allocating tons of hugepages and reduce free memory. >> >> > >> >> > What I did was: >> >> >   # echo 0 > /proc/sys/vm/compact_memory >> >> > >> >> > Hmm, I see this kind of error at migation for the 1st time.. >> >> > my.config is attached. Hmm... ? >> >> > >> >> > (I'm sorry I'll be offline soon.) >> >> >> >> That's ok, thanks you for the report. I'm afraid I made little progress >> >> as I spent most of the day on other bugs but I do have something for >> >> you. >> >> >> >> First, I reproduced the problem using your .config. However, the problem does >> >> not manifest with the .config I normally use which is derived from the distro >> >> kernel configuration (Debian Lenny). So, there is something in your .config >> >> that triggers the problem. I very strongly suspect this is an interaction >> >> between migration, compaction and page allocation debug. >> > >> > I unexpecedly had the time to dig into this. Does the following patch fix >> > your problem? It Worked For Me. >> >> Nice catch during shot time. Below is comment. >> >> > >> > ==== CUT HERE ==== >> > mm,compaction: Map free pages in the address space after they get split for compaction >> > >> > split_free_page() is a helper function which takes a free page from the >> > buddy lists and splits it into order-0 pages. It is used by memory >> > compaction to build a list of destination pages. If >> > CONFIG_DEBUG_PAGEALLOC is set, a kernel paging request bug is triggered >> > because split_free_page() did not call the arch-allocation hooks or map >> > the page into the kernel address space. >> > >> > This patch does not update split_free_page() as it is called with >> > interrupts held. Instead it documents that callers of split_free_page() >> > are responsible for calling the arch hooks and to map the page and fixes >> > compaction. >> >> Dumb question. Why can't we call arch_alloc_page and kernel_map_pages >> as interrupt disabled? > > In theory, it isn't known what arch_alloc_page is going to do but more > practically kernel_map_pages() is updating mappings and should be > flushing all the TLBs. It can't do that with interrupts disabled. > > I checked X86 and it should be fine but only because it flushes the > local CPU and appears to just hope for the best that this doesn't cause > problems. Okay. >> And now compaction only uses split_free_page and it is exposed by mm.h. >> I think it would be better to map pages inside split_free_page to >> export others.(ie, making generic function). > > I considered that and it would not be ideal. It would have to disable and > reenable interrupts as each page is taken from the list or alternatively > require that the caller not have the zone lock taken. The latter of these > options is more reasonable but would still result in more interrupt enabling > and disabling. > > split_free_page() is extremely specialised and requires knowledge of the > page allocator internals to call properly. There is little pressure to > make this easier to use at the cost of increased locking. > >> If we can't do, how about making split_free_page static as static function? >> And only uses it in compaction. >> > > It pretty much has to be in page_alloc.c because it uses internal > functions of the page allocator - e.g. rmv_page_order. I could move it > to mm/internal.h because whatever about split_page, I can't imagine why > anyone else would need to call split_free_page. Yes. Then, Let's add comment like split_page. :) /* * Note: this is probably too low level an operation for use in drivers. * Please consult with lkml before using this in your driver. */ > > -- > Mel Gorman > Part-time Phd Student                          Linux Technology Center > University of Limerick                         IBM Dublin Software Lab > -- Kind regards, Minchan Kim