Date: Thu, 19 Aug 2010 11:20:55 +0100
From: Chris Webb <chris@arachsys.com>
To: Christoph Lameter <cl@linux-foundation.org>
Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com>,
        Wu Fengguang <fengguang.wu@intel.com>,
        Minchan Kim <minchan.kim@gmail.com>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
        Pekka Enberg <penberg@cs.helsinki.fi>,
        Andi Kleen <andi@firstfloor.org>
Subject: Re: Over-eager swapping
Message-ID: <20100819102055.GK2370@arachsys.com>
References: <20100804032400.GA14141@localhost>
 <20100804095811.GC2326@arachsys.com>
 <20100804114933.GA13527@localhost>
 <20100804120430.GB23551@arachsys.com>
 <20100818143801.GA9086@localhost>
 <20100818144655.GX2370@arachsys.com>
 <20100818152103.GA11268@localhost>
 <1282147034.77481.33.camel@useless.localdomain>
 <20100818155825.GA2370@arachsys.com>
 <alpine.DEB.2.00.1008181112510.6294@router.home>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <alpine.DEB.2.00.1008181112510.6294@router.home>
User-Agent: Mutt/1.5.20 (2009-06-14)
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1414
Lines: 36

Christoph Lameter <cl@linux-foundation.org> writes:

> On Wed, 18 Aug 2010, Chris Webb wrote:
> 
> > > != 0.  And even then, zone reclaim should only reclaim file pages, not
> > > anon.  In theory...
> >
> > Hi. This is zero on all our machines:
> >
> > # sysctl vm.zone_reclaim_mode
> > vm.zone_reclaim_mode = 0
> 
> Set it to 1.

I tried this on a handful of the problem hosts before re-adding their swap.
One of them now runs without dipping into swap. The other three I tried had
the same behaviour of sitting at zero swap usage for a while, before
suddenly spiralling up with %wait going through the roof. I had to swapoff
on them to bring them back into a sane state. So it looks like it helps a
bit, but doesn't cure the problem.

I could definitely believe an explanation that we're swapping in preference
to allocating remote zone pages somehow, given the imbalance in free memory
between the nodes which we saw. However, I read the documentation for
vm.zone_reclaim_mode, which suggests to me that when it was set to zero,
pages from remote zones should be allocated automatically in preference to
swap given that zone_reclaim_mode & 4 == 0?

Cheers,

Chris.
--
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/