linux-kernel - Re: [PATCH resend] mm: get rid of CONFIG_STACK_GROWSUP || CONFIG

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Date:	Wed, 4 May 2011 10:28:36 -0700 (PDT)
From:	Hugh Dickins <hughd@...gle.com>
To:	Michal Hocko <mhocko@...e.cz>
cc:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH resend] mm: get rid of CONFIG_STACK_GROWSUP ||
 CONFIG_IA64

On Wed, 4 May 2011, Michal Hocko wrote:
> 
> This case is obscure enough already because we are using VM_GROWSUP to
> declare expand_stack_upwards in include/linux/mm.h

Ah yes, I didn't notice that it was already done that way there
(closer to the definitions of VM_GROWSUP so not as bad).

> while definition is guarded by CONFIG_STACK_GROWSUP||CONFIG_IA64. 
> What the patch does is just "make it consistent" thing. I think we
> should at least use CONFIG_STACK_GROWSUP||CONFIG_IA64 at both places if
> you do not like VM_GROWSUP misuse.

If it's worth changing anything, yes, that would be better.

> 
> > Not a nack: others may well disagree with me.
> > 
> > And, though I didn't find time to comment on your later "symmetrical"
> > patch before it went into mmotm, I didn't see how renaming expand_downwards
> > and expand_upwards to expand_stack_downwards and expand_stack_upwards was
> > helpful either - needless change, and you end up using expand_stack_upwards
> > on something which is not (what we usually call) the stack.
> 
> OK, I see your point. expand_stack_upwards in ia64_do_page_fault can be
> confusing as well. Maybe if we stick with the original expand_upwards
> and just make expand_downwards symmetrical without renameing to
> "_stack_" like the patch does? I can rework that patch if there is an
> interest. I would like to have it symmetrical, though, because the
> original code was rather confusing.

Yes, what I suggested before was an expand_upwards, an expand_downwards
and an expand_stack (with mod to fs/exec.c to replace its call to
expand_stack_downwards by direct call to expand_downwards).

But it's always going to be somewhat confusing and asymmetrical
because of the ia64 register backing store case.

Hugh
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