linux-kernel - Re: [PATCH][2/2] double stack limit (rfc)

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Message-Id: <20070323142327.afc66cb8.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Fri, 23 Mar 2007 14:23:27 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	"Tony Luck" <tony.luck@...el.com>
Cc:	linux-ia64@...r.kernel.org, dmosberger@...il.com,
	surinder.kumar@...cle.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][2/2] double stack limit (rfc)

On Thu, 22 Mar 2007 21:56:03 -0700
"Tony Luck" <tony.luck@...el.com> wrote:

> On 3/22/07, KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
> > I hear some people says that "When I set stack-size-limit to 32M,
> > I want to use 32M of memory stack..." and register-stack expansion can
> > fail because stack is used up by memory-stack.
> 
> An interesting dilemma.  If you apply this patch though, you might
> get someone complain that they set the stack limit to 32M, but
> execution continued as the program ran all the way to 64M!
> 
yes, consumes twice mem at bad case.  

> Possibly you might argue that each of the memory stack and the
> RBS stack should be allowed to grow to the stacklimit ... in which
> case you'd need a more invasive patch that made separate vma
> for each of the stack and the RBS stack, and checked at fault
> time each would be allowed to grow to the stack limit. But I'm
> not sure that I like that ... ia64 happens to split different objects
> in the stack between the RBS and the memory stack depending
> on whether they happen to be allocated by the compiler to
> stack registers (r32-r127) or to actual memory locations.  Both
> types of allocation contribute to the total "stack" size of the
> process so the existing behaivour of keeping the sum of the
> size of the RBS stack and the memory stack below the
> stack limit seems quite reasonable. 

I explained the same thing to my cusotmers ;). I posted this as RFC.
I'd like to hear other opinions, too.

-Kame
Note: [1/2] patch is just a bug fix. sorry for mixing.

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