linux-kernel - Re: [PATCH] slab: fix slab flags for archs use alignment larger 64-bit

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Date:	Fri, 13 Feb 2009 15:11:36 +0100
From:	Giuseppe CAVALLARO <peppe.cavallaro@...com>
To:	Pekka Enberg <penberg@...helsinki.fi>
Cc:	Paul Mundt <lethal@...ux-sh.org>, linux-kernel@...r.kernel.org,
	linux-sh@...r.kernel.org, linux-mm@...r.kernel.org,
	Christoph Lameter <cl@...ux-foundation.org>
Subject: Re: [PATCH] slab: fix slab flags for archs use alignment larger 
 64-bit

Giuseppe CAVALLARO wrote:
> Pekka Enberg wrote:
>   
>> Hi Giuseppe,
>>
>> On Fri, Feb 13, 2009 at 12:46 PM, Giuseppe CAVALLARO
>> <peppe.cavallaro@...com> wrote:
>>   
>>     
>>> 1) LOG with my patch:
>>> root@...ux:~# cat /proc/meminfo | grep Slab
>>> Slab:             2612 kB
>>>
>>> 2) LOG without my patch:
>>> root@...ux:~# cat /proc/meminfo | grep Slab
>>> Slab:             2504 kB
>>>     
>>>       
>> That's not too bad. I assume it's L1_CACHE_BYTES set to 32 bytes? 
>>     
> you are perfectly right.
>   
>> One big problem with your patch is that on some MIPS configurations
>> ARCH_KMALLOC_MINALIGN is as big as 128.
>>     
> Agree again and problem understood... thanks!
>   
>> So if you're going to do this, you can't use ARCH_KMALLOC_MINALIGN directly but add a some
>> SLAB_MAX_DEBUG_ALIGN which can be overridden by architecture code.
>>   
>>     
> If you like, I can prepare a patch in any case.
> Then we can decide if it actually adds complexity and discard it.
> Otherwise we could maintain it.
>   
>> One obvious question, though, is whether all this is worth the added
>> complexity. I mean, we've managed "just fine" without it for years.
>> Paul, thoughts?
>>
>>                                         Pekka
>>   
>>     
Hi!
as promised, patches attached.
At any rate, (this is just my feeling) although we add more complexity
this kind of 'fixes' can actually help users to debug.
So, complexity is welcome especially in these scenarios (debug on, users
in panic mode :-)).
Let me know.
Cheers,
Peppe

View attachment "0001-slab-fix-the-debug-information-with-different-align.patch" of type "text/plain" (1340 bytes)

View attachment "0002-sh-add-the-default-value-for-ARCH_SLAB_MAX_DEBUG_AL.patch" of type "text/plain" (814 bytes)