Kyle Moffett wrote:
> On Oct 12, 2007, at 01:37:23, Al Boldi wrote:
> > You have a point, and resource-controllers can probably control DoS
> > a lot better, but the they also incur more overhead. Think of this
> > "lockout prevention" patch as a near zero overhead safety valve.
>
> But why do you need to add "lockout prevention" if it already
> exists?
I said this before, but I'll say it again: it's about overhead!
> With CFS' extremely efficient per-user-scheduling (hopefully
> soon to be the default) there are only two forms of lockout by non-
> root processes: (1) Running out of PIDs in the box's PID-space
> (think tens or hundreds of thousands of processes), or (2) Swap-
> storming the box to death. To put it bluntly trying to reserve free
> PID slots is attacking the wrong end of the problem and your so
> called "lockout prevention" could very easily ensure that 10 PIDs are
> available even if the user has swapstormed the box with the PIDs he
> does have.
I think you are reading this wrong. It's not about reserving PIDs, it's
about exceeding the max-threads limit. This limit is global and affects
every user including root, which is good, as this allows the sysadmin to
fence the system into a controllable state. So once the system reaches the
fence, sysadmin-intervention allows root to exceed the fence.
Again, this is much nicer with real resource-controllers, but again it's also
more overhead.
Thanks!
--
Al
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