linux-kernel - Re: [Bug #11342] Linux 2.6.27-rc3: kernel BUG at mm/vmalloc.c

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Date:	Wed, 27 Aug 2008 03:23:16 +0300
From:	Adrian Bunk <bunk@...nel.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	"Alan D. Brunelle" <Alan.Brunelle@...com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Kernel Testers List <kernel-testers@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Ingo Molnar <mingo@...e.hu>, linux-embedded@...r.kernel.org
Subject: Re: [Bug #11342] Linux 2.6.27-rc3: kernel BUG at mm/vmalloc.c -
	bisected

On Tue, Aug 26, 2008 at 04:51:52PM -0700, Linus Torvalds wrote:
> 
> 
> On Wed, 27 Aug 2008, Adrian Bunk wrote:
> > > 
> > > We're much better off with a 1% code-size reduction than forcing big 
> > > stacks on people. The 4kB stack option is also a good way of saying "if it 
> > > works with this, then 8kB is certainly safe".
> > 
> > You implicitely assume both would solve the same problem.
> 
> I'm just saying that your logic doesn't hold water.
> 
> If we can save kernel stack usage, then a 1% increase in kernel size is 
> more than worth it.

>From some tests the size increase seems to become bigger for smaller 
kernels, but I don't have any really good data.


An interesting question is why most of our architectures for embedded 
devices only offer bigger stacks:

The only architectures offering a 4kB stacks option are:
- m68knommu
- sh
- 32bit x86

The following architectures that are used in embedded devices 
always use 8kB stacks (or bigger) in your tree:
- arm
- avr32
- blackfin
- cris
- frv
- h8300
- m32r
- m68k
- mips
- mn10300 (has an #ifdef CONFIG_4KSTACKS but no kconfig option)
- powerpc
- xtensa


> > While 4kB stacks are something we anyway never got 100% working
> 
> What? Don't be silly. 
> 
> Linux _historically_ always used 4kB stacks.
> 
> No, they are likely not usable on x86-64, but dammit, they should be more 
> than usable on x86-32 still.


When did we get callpaths like like nfs+xfs+md+scsi reliably 
working with 4kB stacks on x86-32?


>...
> 			Linus

cu
Adrian

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed

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