linux-kernel - Re: [PATCH 0/3] make mapped executable pages the first class citizen

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Date:	Wed, 24 Jun 2009 10:49:05 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	David Howells <dhowells@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Christoph Lameter <cl@...ux-foundation.org>,
	"hannes@...xchg.org" <hannes@...xchg.org>,
	"peterz@...radead.org" <peterz@...radead.org>,
	"riel@...hat.com" <riel@...hat.com>,
	"tytso@....edu" <tytso@....edu>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"elladan@...imo.com" <elladan@...imo.com>,
	"npiggin@...e.de" <npiggin@...e.de>,
	"minchan.kim@...il.com" <minchan.kim@...il.com>
Subject: Re: [PATCH 0/3] make mapped executable pages the first class
	citizen

On Wed, Jun 24, 2009 at 10:43:21AM +0800, KOSAKI Motohiro wrote:
> > On Tue, Jun 23, 2009 at 10:43:57PM +0800, David Howells wrote:
> > > Wu Fengguang <fengguang.wu@...el.com> wrote:
> > > 
> > > > David, could you try running this when it occurred again?
> > > > 
> > > >         make Documentation/vm/page-types
> > > >         Documentation/vm/page-types --raw  # run as root
> > > 
> > > Okay.  I managed to catch it between the first and second OOMs, and ran the
> > > command you asked for.
> > 
> > Thank you!
> > 
> > > 0x0000000000000000	    142261      555  ________________________________	
> > > 0x0000000000000400	      6797       26  __________B_____________________	buddy
> > 
> > The buddy+free numbers are pretty high. 26MB PG_buddy pages means much
> > more actual free pages. So I bet the 555MB no-flag pages are mostly free pages.
> 
> You mean our VM can make OOM although it have 600MB free pages?

Not exactly from one of the previous OOM messages:

DMA: 1*4kB 1*8kB 0*16kB 0*32kB 1*64kB 0*128kB 1*256kB 1*512kB 1*1024kB 1*2048kB 0*4096kB = 3916kB
DMA32: 576*4kB 15*8kB 1*16kB 0*32kB 1*64kB 0*128kB 1*256kB 1*512kB 1*1024kB 0*2048kB 0*4096kB = 4296kB

It looks like something goes wrong with the buddy system?

Thanks,
Fengguang
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