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From: Eric Sandeen <sandeen@redhat.com>
To: Arjan van de Ven <arjan@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] reduce large do_mount stack usage with noinlines
Date: Wed, 06 Feb 2008 17:01:32 -0600	[thread overview]
Message-ID: <47AA3C4C.6080004@redhat.com> (raw)
In-Reply-To: <20080206145439.4ef971f2@laptopd505.fenrus.org>

Arjan van de Ven wrote:
> On Wed, 6 Feb 2008 14:34:57 -0800
> Andrew Morton <akpm@linux-foundation.org> wrote:
> 
>> Does the patch actually help?  I mean, if a() calls b() and both use N
>> bytes of locals, our worst-case stack usage remains ~2N whether or
>> not b() was inlined in a()?  In fact, uninlining makes things a
>> little worse due to callframe stuff.
> 
> it gets interesting at the three-way..
> if a() calls b() and then calls c(), and they all use N,
> the total usage is now 3N not 2N.

*nod*

It'd be nice if it could be max of (a,b,c) though.  Or maybe compilers
don't work that way.  :)

> (although current gcc is already somewhat smarter about this, and 3N might actually be 2N for some cases)

on x86, gcc 4.1.2, do_mount goes from 360 to 112 bytes w/ the patch I sent.

with gcc 4.3, it goes from 364 to 104.

-ERic

  reply	other threads:[~2008-02-06 23:01 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-02-06 22:13 Eric Sandeen
2008-02-06 22:34 ` Andrew Morton
2008-02-06 22:54   ` Arjan van de Ven
2008-02-06 23:01     ` Eric Sandeen [this message]
2008-02-06 22:55   ` Eric Sandeen
2008-02-06 23:11   ` Eric Sandeen
2008-02-06 23:22     ` Andrew Morton
2008-02-06 23:34       ` Eric Sandeen
2008-02-06 23:46         ` Andrew Morton
2008-02-07 23:08       ` Eric Sandeen
2008-02-07 23:23         ` Arjan van de Ven
2008-02-07 23:26         ` Andrew Morton
2008-02-08 16:50       ` Andi Kleen
2008-02-08 16:54         ` Eric Sandeen
2008-02-08 17:23           ` Al Viro

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