Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754073Ab0DTIpQ (ORCPT ); Tue, 20 Apr 2010 04:45:16 -0400 Received: from gir.skynet.ie ([193.1.99.77]:49930 "EHLO gir.skynet.ie" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753857Ab0DTIpO (ORCPT ); Tue, 20 Apr 2010 04:45:14 -0400 Date: Tue, 20 Apr 2010 09:44:54 +0100 From: Mel Gorman To: Minchan Kim Cc: KAMEZAWA Hiroyuki , linux-kernel@vger.kernel.org, akpm@linux-foundation.org, "linux-mm@kvack.org" , "kosaki.motohiro@jp.fujitsu.com" Subject: Re: error at compaction (Re: mmotm 2010-04-15-14-42 uploaded Message-ID: <20100420084454.GD19264@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> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.17+20080114 (2008-01-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5000 Lines: 112 On Tue, Apr 20, 2010 at 05:32:13PM +0900, Minchan Kim wrote: > 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. > */ > I can, but the comment that was there says it's like split_page except the page is already free. This also covers not using it in a driver. -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/