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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