linux-kernel - Re: Re[2]: [PATCH][v2] fork

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Message-Id: <20081211142611.1790a62a.akpm@linux-foundation.org>
Date:	Thu, 11 Dec 2008 14:26:11 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Yuri Tikhonov <yur@...raft.com>
Cc:	linux-kernel@...r.kernel.org, linuxppc-dev@...abs.org,
	Geert.Uytterhoeven@...ycom.com, viro@...iv.linux.org.uk,
	dhowells@...hat.com, miltonm@....com, wd@...x.de, dzu@...x.de,
	yanok@...raft.com
Subject: Re: Re[2]: [PATCH][v2] fork_init: fix division by zero

On Fri, 12 Dec 2008 01:22:32 +0300
Yuri Tikhonov <yur@...raft.com> wrote:

> > so how about avoiding the nasty ifdefs and doing
> 
>  I'm OK with the approach below, but, leading resulting to the same, 
> this involves some overhead to the code where there was no this 
> overhead before this patch: e.g. your implementation is finally boils 
> down to ~5 times more processor instructions than there were before,
> plus operations with stack for the 'm' variable.
> 
>  On the other hand, my approach with nasty (I agree) ifdefs doesn't 
> lead to overheads to the code which does not need this: i.e. the most 
> common situation of small PAGE_SIZEs. Big PAGE_SIZE is the exception, 
> so I believe that the more common cases should not suffer because of 
> this.

yes, but...

> > --- a/kernel/fork.c~fork_init-fix-division-by-zero
> > +++ a/kernel/fork.c
> > @@ -69,6 +69,7 @@
> >  #include <asm/mmu_context.h>
> >  #include <asm/cacheflush.h>
> >  #include <asm/tlbflush.h>
> > +#include <asm/div64.h>
> >  
> >  /*
> >   * Protected counters by write_lock_irq(&tasklist_lock)
> > @@ -185,10 +186,15 @@ void __init fork_init(unsigned long memp

This is __init code and it gets thrown away after bootup.
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