From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail172.messagelabs.com (mail172.messagelabs.com [216.82.254.3]) by kanga.kvack.org (Postfix) with SMTP id 658FE6B01F0 for ; Mon, 19 Apr 2010 22:39:48 -0400 (EDT) Received: by iwn14 with SMTP id 14so3731932iwn.22 for ; Mon, 19 Apr 2010 19:39:47 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20100419193919.GB19264@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> Date: Tue, 20 Apr 2010 11:39:46 +0900 Message-ID: Subject: Re: error at compaction (Re: mmotm 2010-04-15-14-42 uploaded From: Minchan Kim Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org To: Mel Gorman Cc: KAMEZAWA Hiroyuki , linux-kernel@vger.kernel.org, akpm@linux-foundation.org, "linux-mm@kvack.org" , "kosaki.motohiro@jp.fujitsu.com" List-ID: 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 >> > =C2=A0# echo 0 > /proc/sys/vm/compaction >> > >> > I see following. >> > >> > My enviroment was >> > =C2=A0 2.6.34-rc4-mm1+ (2010-04-15-14-42) (x86-64) CPUx8 >> > =C2=A0 allocating tons of hugepages and reduce free memory. >> > >> > What I did was: >> > =C2=A0 # 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 d= istro >> kernel configuration (Debian Lenny). So, there is something in your .con= fig >> that triggers the problem. I very strongly suspect this is an interactio= n >> 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. > > =3D=3D=3D=3D CUT HERE =3D=3D=3D=3D > mm,compaction: Map free pages in the address space after they get split f= or 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? It's deadlock issue or latency issue? I don't found any comment about it. It should have added the comment around that functions. :) 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). If we can't do, how about making split_free_page static as static function? And only uses it in compaction. --=20 Kind regards, Minchan Kim -- 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