linux-kernel - Re: backing up ext4 fs, system unresponsive, thrashing like crazy even though swap is unused

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Message-ID: <20121125225954.GA14653@mobil.systemanalysen.net>
Date:	Sun, 25 Nov 2012 23:59:55 +0100
From:	Roland Eggner <edvx1@...temanalysen.net>
To:	Dimitrios Apostolou <jimis@....net>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: backing up ext4 fs, system unresponsive, thrashing like crazy
 even though swap is unused

On 2012-11-25 Sunday at 21:30 +0200 Dimitrios Apostolou wrote:
> On Sun, 2012-11-25 at 15:55 +0200, Dimitrios Apostolou wrote:
> > on an old PIII-500MHz laptop, 128MB RAM, kernel 3.6.6, I started a
> > backup process (tar|xz -4, nice'd and ionice'd -c3) from ext4 on local
> > ATA disk to ext3 on external USB disk (USB-2.0 port on PCMCIA card).
> > Even though earlier system load was minimal, free memory was plenty, the
> > system now is unresponsive and is thrashing the disk, but the swapfile
> > is rarely touched.
> 
> I'm now having the same experience even though I replaced xz (which
> needed ~50MB RAM) with gzip. Even though I feel the realtime root shell
> is a bit more responsive than before, the OOM killer is out killing 
> small processes like syslog-ng and systemd-logind... The
> ext4_inode_cache slab is taking almost all my memory (117MB). Please
> advise!

Hello Dimitrios,

I would try a 2.6.27.* kernel, for following reasons:

(1)  Kernel development since 2.6.27 achieved significant performance 
improvements at the cost of exploding memory consumption by the kernel for 
_internal_  data structures.  I am currently using a 3.2.34 kernel on a Notebook 
with 4 G RAM.  0,5 … 1 G RAM is usually occupied just by kernel slab [1];  this 
memory cannot be swapped, it cannot be released by other means than rebooting, 
and there seems to be  _no_  adjustment to memory pressure.  I am surprised, 
that you have managed to boot a 3.6.* kernel at all with only 128 M RAM.

(2)  At the time, when I used a PIII-Notebook, kernels 2.6.27 to 2.6.29 where 
current.  Thus chances are good, that a 2.6.27.* kernel will support chipset, 
PCI bus and devices of your notebook.  2.6.27 got longterm maintainance, the 
latest release in the linux-stable git repository is 2.6.27.62.
So Q @ LKML community:
Does anybody know a x86 distribution or live-CD using a 2.6.27.* kernel?

[1]  Picture described in my LKML message
Date:  Fri, 20 Jan 2012 01:08:00 +0100
Subject:  Re: [kmemleak report 1/2] kernel 3.1.6, x86_64: mm, xfs ?, vfs ?
remained the same with  _every_  3.1.* and 3.2.* kernel tried so far.

-- 
Roland

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