Re: [BUG] in 2.6.25-rc3 with 64k page size and SLUB_DEBUG_ON

[Jens Osterkamp <Jens.Osterkamp@gmx.de>]

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On Thursday 13 March 2008, Christoph Lameter wrote:
> On Wed, 12 Mar 2008, Jens Osterkamp wrote:
> 
> > I added a printk in kmalloc and the size seems to be 0x4000.
> 
> Hmmmm... So kmalloc_index returns 14. This should all be fine.
> 
> However, with slub_debug the size of the 16k kmalloc object is 
> actually a bit larger than 0x4000. The caller must not expect the object 
> to be aligned to a 16kb boundary. Is that the case?

Actually the caller expects exactly that. The kmalloc that I saw was coming
from alloc_thread_info in dup_task_struct. For 4k pages this maps to 
__get_free_pages whereas for 64k pages it maps to kmalloc.
The result of __get_free_pages seem to be aligned and kmalloc (with slub_debug)
of course not. That explains the 4k/64k difference and the crash I am seeing...
but I can't think of a reasonable fix right now as I don't understand the
reason for the difference in the allocation code (yet).

Gruß,
	Jens

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