Re: High load average on disk I/O on 2.6.17-rc3

[Erik Mouw <erik@harddisk-recovery.com>]

On Sun, May 07, 2006 at 09:50:39AM -0700, Andrew Morton wrote:
> This is probably because the number of pdflush threads slowly grows to its
> maximum.  This is bogus, and we seem to have broken it sometime in the past
> few releases.  I need to find a few quality hours to get in there and fix
> it, but they're rare :(
> 
> It's pretty harmless though.  The "load average" thing just means that the
> extra pdflush threads are twiddling thumbs waiting on some disk I/O -
> they'll later exit and clean themselves up.  They won't be consuming
> significant resources.

Not completely harmless. Some daemons (sendmail, exim) use the load
average to decide if they will allow more work. A local user could
create a mail DoS by just copying a couple of large files around.
Zeniv.linux.org.uk mail went down due to this. See
http://lkml.org/lkml/2006/3/28/70 .


Erik

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