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    SubjectRe: [patch 016/104] epoll: introduce resource usage limits
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    On Fri, Jan 23, 2009 at 6:06 PM, Greg KH <gregkh@suse.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@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.

    Why not using a ulimit for this kind of stuff ?

    Regards

    Bastien


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