Re: top stack (l)users for 2.5.69

[Martin J. Bligh]

>> Does 2.5 use a separate interrupt stack? (Excuse my ignorance; I 
>> haven't been paying attention.) Total stack-page usage in the 2.4 
>> model, at any rate, is the sum of the task struct, the usage of any 
>> task-level thread (system calls, pretty much), any softirq (including 
>> the network protocol & routing handlers, and any netfilter modules), 
>> and some number of possibly-nested hard interrupts.
> 
> Depends on the architecture. s390 does, ppc didn't as of 2.4.2, the
> rest I'm not sure about. But this is another requirement for stack
> reduction to 4k for most platforms, if not all.

There are patches to make i386 do this (and use 4K stacks as a config option) 
from Dave Hansen and Ben LaHaise in 2.5-mjb tree. 
 
>> One thing that would help (aside from separate interrupt stacks) 
>> would be a guard page below the stack. That wouldn't require any 
>> physical memory to be reserved, and would provide positive indication 
>> of stack overflow without significant runtime overhead.
> 
> Yes, that should work. It needs some additional code in the page fault
> handler to detect this case, but that shouldn't slow the system down
> too much.

There's stack overflow detection in there as well.

M.