linux-kernel - Re: [PATCH] Create initial stack independent of PAGE

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Message-Id: <20100212184941.73BE.A69D9226@jp.fujitsu.com>
Date:	Fri, 12 Feb 2010 18:51:09 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Michael Neuling <mikey@...ling.org>
Cc:	kosaki.motohiro@...fujitsu.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	Helge Deller <deller@....de>,
	Americo Wang <xiyou.wangcong@...il.com>,
	Anton Blanchard <anton@...ba.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Create initial stack independent of PAGE_SIZE

> In message <20100212161305.73B2.A69D9226@...fujitsu.com> you wrote:
> > > Currently we create the initial stack based on the PAGE_SIZE.  This is
> > > unnecessary.  
> > 
> > I don't think this is enough explanation. In past mail, you described
> > why page size dependency is harmful. I hope you add it into the patch
> > description.
> 
> I don't think it's harmful, it's just irrelevant.  Stack size is
> independent of page size.  

ok.

> > IOW, we don't need to change the unnecessary-but-non-harmful behavior.
> > 
> > > 
> > > This creates this initial stack independent of the PAGE_SIZE.
> > > 
> > > It also bumps up the number of 4k pages allocated from 20 to 32, to
> > > align with 64K page systems.
> > 
> > Why do we need page-aligning? Do you mean this code doesn't works on
> > 128K (or more larger) page systems?
> 
> If the "random" setting is not a common multiple of the 4k and 64k
> pages, they will end up getting aligned differently, hence causing what
> we are trying to avoid in the first place with this patch.

I see. ok,
	Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>

> 
> I should probably add this as a comment in the code comment?

probably, It's not big matter.

Thanks :)



> 
> Mikey
> 
> > 
> > 
> > > 
> > > Signed-off-by: Michael Neuling <mikey@...ling.org>
> > > ---
> > > This is the second half of my original patch. This can be targeted for
> > > 2.6.34 as it's just a cleanup.
> > > 
> > > Tested on PPC64 with 4k and 64k pages.
> > > 
> > >  fs/exec.c |    4 +---
> > >  1 file changed, 1 insertion(+), 3 deletions(-)
> > > 
> > > Index: linux-2.6-ozlabs/fs/exec.c
> > > ===================================================================
> > > --- linux-2.6-ozlabs.orig/fs/exec.c
> > > +++ linux-2.6-ozlabs/fs/exec.c
> > > @@ -554,8 +554,6 @@ static int shift_arg_pages(struct vm_are
> > >  	return 0;
> > >  }
> > >  
> > > -#define EXTRA_STACK_VM_PAGES	20	/* random */
> > > -
> > >  /*
> > >   * Finalizes the stack vm_area_struct. The flags and permissions are updat
> ed,
> > >   * the stack is optionally relocated, and some extra space is added.
> > > @@ -630,7 +628,7 @@ int setup_arg_pages(struct linux_binprm 
> > >  			goto out_unlock;
> > >  	}
> > >  
> > > -	stack_expand = EXTRA_STACK_VM_PAGES * PAGE_SIZE;
> > > +	stack_expand = 131072UL; /* randomly 32*4k (or 2*64k) pages */
> > >  	stack_size = vma->vm_end - vma->vm_start;
> > >  	/*
> > >  	 * Align this down to a page boundary as expand_stack
> > 
> > 
> > 



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