From: Mel Gorman <mgorman@suse.de>
Subject: Re: [PATCH 3/3] mm: slub: Default slub_max_order to 0
Date: Fri, 13 May 2011 11:30:09 +0100
Message-ID: <20110513103009.GD3569@suse.de>
References: <alpine.DEB.2.00.1105120942050.24560@router.home>
 <1305213359.2575.46.camel@mulgrave.site>
 <alpine.DEB.2.00.1105121024350.26013@router.home>
 <1305214993.2575.50.camel@mulgrave.site>
 <1305215742.27848.40.camel@jaguar>
 <1305225467.2575.66.camel@mulgrave.site>
 <1305229447.2575.71.camel@mulgrave.site>
 <1305230652.2575.72.camel@mulgrave.site>
 <1305237882.2575.100.camel@mulgrave.site>
 <20110512221506.GM16531@cmpxchg.org>
Mime-Version: 1.0
Content-Type: text/plain; charset=iso-8859-15
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>,
	Pekka Enberg <penberg@kernel.org>, Christoph Lameter <cl@linux.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Colin King <colin.king@canonical.com>,
	Raghavendra D Prabhu <raghu.prabhu13@gmail.com>,
	Jan Kara <jack@suse.cz>, Chris Mason <chris.mason@oracle.com>,
	Rik van Riel <riel@redhat.com>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	linux-mm <linux-mm@kvack.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	linux-ext4 <linux-ext4@vger.kernel.org>
To: Johannes Weiner <hannes@cmpxchg.org>
Return-path: <owner-linux-mm@kvack.org>
Content-Disposition: inline
In-Reply-To: <20110512221506.GM16531@cmpxchg.org>
Sender: owner-linux-mm@kvack.org
List-Id: linux-ext4.vger.kernel.org

On Fri, May 13, 2011 at 12:15:06AM +0200, Johannes Weiner wrote:
> On Thu, May 12, 2011 at 05:04:41PM -0500, James Bottomley wrote:
> > On Thu, 2011-05-12 at 15:04 -0500, James Bottomley wrote:
> > > Confirmed, I'm afraid ... I can trigger the problem with all three
> > > patches under PREEMPT.  It's not a hang this time, it's just kswapd
> > > taking 100% system time on 1 CPU and it won't calm down after I unload
> > > the system.
> > 
> > Just on a "if you don't know what's wrong poke about and see" basis, I
> > sliced out all the complex logic in sleeping_prematurely() and, as far
> > as I can tell, it cures the problem behaviour.  I've loaded up the
> > system, and taken the tar load generator through three runs without
> > producing a spinning kswapd (this is PREEMPT).  I'll try with a
> > non-PREEMPT kernel shortly.
> > 
> > What this seems to say is that there's a problem with the complex logic
> > in sleeping_prematurely().  I'm pretty sure hacking up
> > sleeping_prematurely() just to dump all the calculations is the wrong
> > thing to do, but perhaps someone can see what the right thing is ...
> 
> I think I see the problem: the boolean logic of sleeping_prematurely()
> is odd.  If it returns true, kswapd will keep running.  So if
> pgdat_balanced() returns true, kswapd should go to sleep.
> 
> This?
> 

You're right.

> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 2b701e0..092d773 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2261,7 +2261,7 @@ static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining,
>  	 * must be balanced
>  	 */
>  	if (order)
> -		return pgdat_balanced(pgdat, balanced, classzone_idx);
> +		return !pgdat_balanced(pgdat, balanced, classzone_idx);
>  	else
>  		return !all_zones_ok;
>  }

-- 
Mel Gorman
SUSE Labs

--
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/ .
Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>