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Re: [PATCH v2] MIPS: Alchemy: fix dbdma ring destruction memory debugche

To: Manuel Lauss <manuel.lauss@googlemail.com>
Subject: Re: [PATCH v2] MIPS: Alchemy: fix dbdma ring destruction memory debugcheck.
From: Ralf Baechle <ralf@linux-mips.org>
Date: Thu, 28 Jan 2010 12:22:52 +0100
Cc: Linux-MIPS <linux-mips@linux-mips.org>, Manuel Lauss <manuel.lauss@gmail.com>
In-reply-to: <f861ec6f1001280023n7753c77wfd626d731ddc690a@mail.gmail.com>
References: <1264534773-24909-1-git-send-email-manuel.lauss@gmail.com> <20100127221818.GB26426@linux-mips.org> <f861ec6f1001280023n7753c77wfd626d731ddc690a@mail.gmail.com>
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User-agent: Mutt/1.5.20 (2009-08-17)
On Thu, Jan 28, 2010 at 09:23:56AM +0100, Manuel Lauss wrote:

> >> This fix is only necessary with the SLAB allocator and CONFIG_DEBUG_SLAB
> >> enabled;  non-debug SLAB, SLUB do return nicely aligned addresses,
> >> debug-enabled SLUB currently panics early in the boot process.
> >
> > Queued for 2.6.34 - should this also go into 2.6.33?
> 
> 2.6.33 and .32 at least.  That code has been in there since the dawn of 2.6;
> the fact that nobody has tripped over this so far means that noone build 
> kernels
> with slab debugging (I tripped over this while looking for something else) or
> the slab allocator behaviour changed recently.

The behaviour of the slab has been like this as long as I can remember.
Cherrypicking into the -stable branches as I'm writing this.

> > Have you considered increasing the value ARCH_KMALLOC_MINALIGN which
> > defaults to 8?  Or your own slab cache of suitable alignment?  The latter
> > is more something for frequent allocations.
> 
> I have to admit I know nothing about Linux' memory management.  Are slab
> caches not affected by the what I presume are "guard bytes" inserted into
> the memory areas when slab debug is on?

When creating a slab cache an alignment for objects allocated from this
cache can be specified.

  Ralf

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