linux-kernel - Re: [PATCH] Don't mlock guardpage if the stack is growing up

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Message-ID: <BANLkTikLJPCc5ffobAb5uhdryRqjGhpVAQ@mail.gmail.com>
Date:	Mon, 9 May 2011 16:08:44 -0700
From:	Tony Luck <tony.luck@...il.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	James Bottomley <James.Bottomley@...senpartnership.com>,
	Mikulas Patocka <mikulas@...ax.karlin.mff.cuni.cz>,
	Fenghua Yu <fenghua.yu@...el.com>,
	Hugh Dickins <hughd@...gle.com>, linux-kernel@...r.kernel.org,
	linux-parisc@...r.kernel.org,
	Michel Lespinasse <walken@...gle.com>,
	Oleg Nesterov <oleg@...hat.com>, linux-ia64@...r.kernel.org
Subject: Re: [PATCH] Don't mlock guardpage if the stack is growing up

On Mon, May 9, 2011 at 3:58 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> Ahh, so you never actually have one single mapping that has both flags set?
>
> In that case, I won't even worry about it.

Definitely not for normal processes - I'm not sure how both stacks are
set up for threads.

> One thing I did want to verify: did the mlockall() actually change the
> stack size without that patch? Just to double-check that the patch
> actually did change semantics visibly.

On an unpatched system I see this (lots more than one page of growth -
pages are 64K on this config):
6007fffffff50000-6007fffffff70000 rw-p 00000000 00:00 0
6007fffffff50000-6008000000750000 rw-p 00000000 00:00 0

On a patched system I see (this one has 16K pages - no growth)
600007ffff9d0000-600007ffff9d4000 rw-p 00000000 00:00 0
600007ffff9d0000-600007ffff9d4000 rw-p 00000000 00:00 0

-Tony
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