Re: [git pull] m68k SLUB fix for 2.6.39

David Rientjes
2011-04-28T21:41:53Z

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.