On Wed, 2 May 2007 10:25:47 -0700 (PDT) Christoph Lameter <[email protected]> wrote:
> On Wed, 2 May 2007, Hugh Dickins wrote:
>
> > I presume the answer is just to extend your quicklist work to
> > powerpc's lowest level of pagetables. The only other architecture
> > which is using kmem_cache for them is arm26, which has
> > "#error SMP is not supported", so won't be giving this problem.
>
> In the meantime we would need something like this to disable SLUB in this
> particular configuration. Note that I have not tested this and the <= for
> the comparision with SPLIT_PTLOCK_CPUS may not work (Never seen such a
> construct in a Kconfig file but it is needed here).
>
>
>
> PowerPC: Disable SLUB for configurations in which slab page structs are modified
>
> PowerPC uses the slab allocator to manage the lowest level of the page table.
> In high cpu configurations we also use the page struct to split the page
> table lock. Disallow the selection of SLUB for that case.
>
> [Not tested: I am not familiar with powerpc build procedures etc]
>
> Signed-off-by: Christoph Lameter <[email protected]>
>
> Index: linux-2.6.21-rc7-mm2/arch/powerpc/Kconfig
> ===================================================================
> --- linux-2.6.21-rc7-mm2.orig/arch/powerpc/Kconfig 2007-05-02 10:07:34.000000000 -0700
> +++ linux-2.6.21-rc7-mm2/arch/powerpc/Kconfig 2007-05-02 10:13:37.000000000 -0700
> @@ -117,6 +117,19 @@ config GENERIC_BUG
> default y
> depends on BUG
>
> +#
> +# Powerpc uses the slab allocator to manage its ptes and the
> +# page structs of ptes are used for splitting the page table
> +# lock for configurations supporting more than SPLIT_PTLOCK_CPUS.
> +#
> +# In that special configuration the page structs of slabs are modified.
> +# This setting disables the selection of SLUB as a slab allocator.
> +#
> +config ARCH_USES_SLAB_PAGE_STRUCT
> + bool
> + default y
> + depends on SPLIT_PTLOCK_CPUS <= NR_CPUS
> +
That all seems to work as intended.
However with NR_CPUS=8 SPLIT_PTLOCK_CPUS=4, enabling SLUB=y crashes the
machine early in boot.
Too early for netconsole, no serial console. Wedges up uselessly with
CONFIG_XMON=n, does mysterious repeated uncontrollable exceptions with
CONFIG_XMON=y. This is all fairly typical for a powerpc/G5 crash :(
However I was able to glimpse some stuff as it flew past. Crash started in
flush_old_exec and ended in pgtable_free_tlb -> kmem_cache_free. I don't know
how to do better than that I'm afraid, unless I'm to hunt down a PCIE serial
card, perhaps.
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