Re: [PATCH] fork failures on ix86

Andi Kleen (ak@muc.de)
10 Jul 1998 00:46:19 +0200


kbr@pangea.ca (Kip Rugger) writes:

>
> - I find the problem with fork going flaky to be, in some sense, worse
> than a hard crash, especially on an unattended, unmonitored server.
> Is it possible that a little auditing could reduce the stack back to
> one page?

The main reason when I remember it right to extend the kernel stack was
not increased stack usage, but for putting the task structure at the
bottom of the stack to turn "current" into "sp & MASK". This is important
for good performance on SMP machines. Many non-x86 ports use a dedicated
register for that, but that is not possible for x86 because it has so few.

It turned out that 4k-sizeof(struct task_struct) was too small, so it was
increased to 8k-sizeof(struct task_struct).

If a better way could be found to solve this current problem then the
kernel stack could probably shrinked to a single page again on x86.

The auditing would be major work - at least 1M lines of driver code +
third party code not shipped with the kernel.

-Andi

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