Date: Fri, 23 Jan 2009 09:06:31 -0800
From: Greg KH <gregkh@suse.de>
To: Bron Gondwana <brong@fastmail.fm>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       stable@kernel.org, Justin Forbes <jmforbes@linuxtx.org>,
       Zwane Mwaikambo <zwane@arm.linux.org.uk>,
       "Theodore Ts'o" <tytso@mit.edu>, Randy Dunlap <rdunlap@xenotime.net>,
       Dave Jones <davej@redhat.com>, Chuck Wolber <chuckw@quantumlinux.com>
Subject: Re: [patch 016/104] epoll: introduce resource usage limits
Message-ID: <20090123170631.GB11566@suse.de>
References: <20081203193901.715896543@mini.kroah.org> <20081203194849.GQ8950@kroah.com> <1232686261.9977.1296303473@webmail.messagingengine.com> <20090123051620.GA8122@suse.de> <1232704065.25510.1296328851@webmail.messagingengine.com>
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On Fri, Jan 23, 2009 at 08:47:45PM +1100, Bron Gondwana wrote:
> On Thu, 22 Jan 2009 21:16 -0800, "Greg KH" <gregkh@suse.de> wrote:
> > > This is a kvm virtual machine running on a reasonably beefy external box, but
> > > with 2Gb RAM allocated to the mx instance because that's all kvm would let me
> > > use last time I checked.  We're using KVM so the local copy of the database is
> > > a little further away from the "internet facing side" and so we can build each
> > > machine with our standard FAI setup.
> > 
> > I would suggest just changing this default value then, it's a simple
> > userspace configuration item, and for your boxes, it sounds like a
> > larger value would be more suitable.
> 
> Yes - I've pushed it up to 4096 now.  Should be plenty!
> 
> I guess Postfix is a bit of an odd case here.   It runs lots of processes, yet
> uses epoll within many of them as well - sort of a historical design in some ways,
> but also to enforce maximum privilege separation with many of the daemons able to
> be run under chroot with limited capabilities.
> 
> So I guess I have a few questions left:
> 
> 1) is this value ever supposed to be hit in practice by non-malicious software?
>    If not, it appears 128 is too low.

It does appear a bit low.  What looks to you like a good value to use as
a default?

> 2) if we're going to stick with 128, is there any way to query the kernel as to how
>    close to the limit it's getting?  As an example, our system checks poll
>    /proc/sys/fs/file-max every 2 minutes, and warn us if its getting "full".

Good idea, we should report this somewhere for the very reasons you
suggest.  Can you write up a patch to do this?  If not, I'll see what I
can do.

thanks,

greg k-h
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