linux-kernel - Re: Fwd: kswapd issues + kernel 2.4.21-32.0.1.ELsmp

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Date:	Sun, 1 Apr 2007 13:21:28 +0300
From:	Dan Aloni <da-x@...atomic.org>
To:	Pedram M <pmessri@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Fwd: kswapd issues + kernel 2.4.21-32.0.1.ELsmp

On Sat, Mar 31, 2007 at 01:11:29AM -0700, Pedram M wrote:
> Hi,
> 
> I've seen this around, and have heard about it in forums and else-where,
> could somebody enlighten me with more information or with experiences
> they have had.  Looks like kswapd begins to eat CPU dramatically till the
> box eventually locks up.

My experience with kswapd eating a lot of CPU tells that this particular 
problem with Linux 2.4 manifests itself on this scenario:

 * No swap is configured (we are blessed with RAM).

_AND_:

 * A lot of memory is allocated (for my case: a lot of anonymous pages 
used for applications).

Looking at this problem with kdb, I noticed that the CPU spends a lot 
of time in swap_out(), even though there are no swap devices...

So...

mm/vmscan.c, replace swap_out with this:

    static int swap_out(zone_t * classzone)
    {
            return 0;
    }

Now, this might raise some eyebrows for those MM gurus reading this
mail but I assure you I've been doing this for a lot of time (and 
a lot of machines) on 2.4.27, and it took care of my kswapd issues
quite nicely.

I hope it helps...

-- 
Dan Aloni
XIV LTD, http://www.xivstorage.com
da-x (at) monatomic.org, dan (at) xiv.co.il
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