Messages in this thread | | | Date | Tue, 27 Jan 2009 21:48:07 -0800 (PST) | From | Davide Libenzi <> | Subject | Re: [patch 016/104] epoll: introduce resource usage limits |
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On Wed, 28 Jan 2009, Willy Tarreau wrote:
> On Tue, Jan 27, 2009 at 09:26:30PM -0800, Greg KH wrote: > > On Tue, Jan 27, 2009 at 08:10:41PM -0800, Davide Libenzi wrote: > > > In my servers, I know if they are going to be loaded, and I bump NFILES > > > (and a few other things) to the correct place. Since many of those > > > limits do not actually pre-allocate any resource, I don't need to wait and > > > monitor the values, before taking proper action. > > > > But what about people who want to know what the current usages are, so > > that they _can_ monitor things and adjust them on the fly if things are > > about to go boom? > > > > I see no reason why we can't leave the value where it is today, and add > > the ability to both turn the limits off entirely, and also report our > > current usage. That keeps the DOS from happening on "default" systems, > > and lets admins have an idea if they need to bump up the values on their > > systems as well. > > > > I don't understand your objection to allowing the usage to be monitored. > > Agreed. If sysadmins get trapped by the upgrade, the fix for an > hypotethical DoS is a 100%-certain DoS by itself. The general sense > that "if it's not broken, don't fix it" applies here as well. The > server's sysadmin should not be bothered by a security upgrade (anyway, > after a few minutes of havoc in prod, he will revert to previous version > without trying to understand any further). But the campus sysadmin having > trouble with local users already spends a lot of time tweaking limits. > Now we offer them a new limit they can tune, they'll happily use it. > Anyway, even at 128 they'll probably lower it down a lot. So basically > we're with a medium value which does not fit any usage.
You know, it's not me that decides what goes of certain trees or not ;) I've been pinged about the problem, and a patch was sent with values that seemed appropriate for typical epoll usages. Epoll is a multiplexing interface, so the thought was that not too many instances were lingering around. Probably the default max_instances should have been made lomem dependent like max_user_watches in the first place, leading to higher max_instances values, with respect of the potential DoS.
- Davide
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