Re: [git pull] m68k SLUB fix for 2.6.39

[David Rientjes]

On Thu, 28 Apr 2011, James Bottomley wrote:

> > Since 4a5fa3590f09 ([PARISC] slub: fix panic with DISCONTIGMEM) from 
> > 2.6.39-rc4, you can't actually select slub on m68k without CONFIG_ADVANCED 
> > and CONFIG_SINGLE_MEMORY_CHUNK because it otherwises defaults to 
> > discontigmem.
> > 
> > James tested hppa64 with my N_NORMAL_MEMORY fix and found that it turned 
> > an SMP box into UP.  If you've tested slub on m68k without regressions, 
> > then perhaps you'd like to add a "|| M68K" to CONFIG_SLUB?
> 
> To be honest, I really don't see that fixing it.  As soon as you
> allocate memory beyond range zero, you move onto a non-zero node as far
> as slub is concerned, and that will oops.
> 

Possible nodes are represented in slub with N_NORMAL_MEMORY, so the 
kmem_cache_node structures are allocated and initialized based on this 
nodemask.  As long as the memory ranges map to nodes set in the nodemask, 
this should be fine.

> I think what the N_NORMAL_MEMORY patch did is just make it take a whiile
> before you start allocating from that range.  Try executing a memory
> balloon on the platform; that was how we first demonstrated the problem
> on parisc.
> 

With parisc, you encountered an oops in add_partial() because the 
kmem_cache_node structure for the memory range returned by page_to_nid() 
was not allocated.  init_kmem_cache_nodes() takes care of this for all 
memory ranges set in N_NORMAL_MEMORY.

Adding Christoph and Pekka to the cc if there is additional concerns about 
slub on this architecture.
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