Re: heap-stack-gap for 2.6
From: Hui Huang (Hui.Huang_at_Sun.COM)
Date: 09/30/04
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- In reply to: Andrea Arcangeli: "Re: heap-stack-gap for 2.6"
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Date: Wed, 29 Sep 2004 15:01:13 -0700 To: Andrea Arcangeli <andrea@novell.com>
Andrea Arcangeli wrote:
>
>>Now another wish - instead of a system-wide property, a per-process
>>mechanism to change heap-stack-gap. Applications that need the gap
>>can set up the appropriate size, while others like Java that manage
>>heap and stack can simply disable the gap. Is it possible?
>
>
> This is a very reasonable request, and yes, this is definitely possible,
> I feel this is a much better feature than the mprotect trapping, which
> is possible too, but it sounds not worth it.
>
> As for the api, should that be a prctl, /proc/<pid>/heap-stack-gap, or a
> brand new syscall? I personally enjoy the /proc/<pid>/heap-stack-gap
> approach, but that's just me, the prctl and syscall would be more
> efficient at runtime (but the point is that this doesn't need to be more
> efficient and echo xx > /proc/<pid>/heap-stack-gap is so much easier to
> play with for experiments)
Hi Andrea,
From our perspective prctl is the most attractive approach. Performance
is not an issue, as it's only used once during startup. The problem
with /proc is that we are not always able to access /proc (e.g.
java code is run with chroot). Stack overflow in chroot'ed program
probably is a corner case, but I'm afraid we'll have to deal with it
if the heap-stack-gap becomes more widespread. System call is better
but we need to remember different syscall numbers on different
platforms.
>
> If we can choose the API together I'll take care of implementing the
> rest. I'd like to still leave a global sysctl for global system safety
> (since most apps needs it and they won't all be required to tune it by
> hand), so that the final number will be choose with:
>
> if (likely(per_process_setting < 0))
> return global_sysctl;
> else
> return per_process_setting;
Sounds good.
thanks,
-hui
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