Messages in this thread | | | Date | Fri, 23 Jan 2009 11:28:38 -0800 (PST) | From | Davide Libenzi <> | Subject | Re: [patch 016/104] epoll: introduce resource usage limits |
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On Fri, 23 Jan 2009, Bron Gondwana wrote:
> On Thu, 22 Jan 2009 21:16 -0800, "Greg KH" <gregkh@suse.de> wrote: > > On Fri, Jan 23, 2009 at 03:51:01PM +1100, Bron Gondwana wrote: > > > On Wed, 03 Dec 2008 11:48 -0800, "Greg KH" <gregkh@suse.de> wrote: > > > > The default value for "max_user_instances" is set to 128, that should be enough too. > > > > > > Our fairly heavily loaded postfix backup mx (lots of spams rejected per day) hit this > > > limit running kernel 2.6.27.8. Any particular reason for it being as low as 128 > > > by default? > > > > Something had to be picked :) > > Fair enough :) > > > > 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. > > 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".
Why? If you know you have a loaded, non multi-user server, just bump the value up and forget about it. An higher value is not going to cost you anything in terms of resource allocation. Adding more /proc code to monitor a silly value, probably is.
- Davide
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