linux-kernel - Re: [patch 016/104] epoll: introduce resource usage limits

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Message-ID: <195c7a900901230924n13ed225dq4aeff8015d22588e@mail.gmail.com>
Date:	Fri, 23 Jan 2009 18:24:24 +0100
From:	Bastien ROUCARIES <roucaries.bastien@...il.com>
To:	Greg KH <gregkh@...e.de>
Cc:	Bron Gondwana <brong@...tmail.fm>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	stable@...nel.org, Justin Forbes <jmforbes@...uxtx.org>,
	Zwane Mwaikambo <zwane@....linux.org.uk>,
	"Theodore Ts'o" <tytso@....edu>,
	Randy Dunlap <rdunlap@...otime.net>,
	Dave Jones <davej@...hat.com>,
	Chuck Wolber <chuckw@...ntumlinux.com>
Subject: Re: [patch 016/104] epoll: introduce resource usage limits

On Fri, Jan 23, 2009 at 6:06 PM, Greg KH <gregkh@...e.de> wrote:
> On Fri, Jan 23, 2009 at 08:47:45PM +1100, Bron Gondwana wrote:
>> On Thu, 22 Jan 2009 21:16 -0800, "Greg KH" <gregkh@...e.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.

Why not using a ulimit for this kind of stuff ?

Regards

Bastien
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