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Subject[PATCH 04/15] mm: update split ptlock Kconfig
Closer attention to the arithmetic shows that neither ppc64 nor sparc
really uses one page for multiple page tables: how on earth could they,
while pte_alloc_one returns just a struct page pointer, with no offset?

Gasp, splutter... arm26 manages it by returning a pte_t pointer cast to
a struct page pointer, then compensating in its pmd_populate. That's
almost as evil as overlaying a struct page with a spinlock_t. But arm26
is never SMP, and we now only poison when SMP, so it's not a problem.

And the PA-RISC situation has been recently improved: CONFIG_PA20
works without the 16-byte alignment which inflated its spinlock_t.

Signed-off-by: Hugh Dickins <>

mm/Kconfig | 6 ++----
1 files changed, 2 insertions(+), 4 deletions(-)

--- mm03/mm/Kconfig 2005-11-07 07:39:59.000000000 +0000
+++ mm04/mm/Kconfig 2005-11-09 14:38:32.000000000 +0000
@@ -125,14 +125,12 @@ comment "Memory hotplug is currently inc
# space can be handled with less contention: split it at this NR_CPUS.
# Default to 4 for wider testing, though 8 might be more appropriate.
# ARM's adjust_pte (unused if VIPT) depends on mm-wide page_table_lock.
-# PA-RISC's debug spinlock_t is too large for the 32-bit struct page.
-# ARM26 and SPARC32 and PPC64 may use one page for multiple page tables.
+# PA-RISC 7xxx's debug spinlock_t is too large for 32-bit struct page.
default "4096" if ARM && !CPU_CACHE_VIPT
- default "4096" if PARISC && DEBUG_SPINLOCK && !64BIT
- default "4096" if ARM26 || SPARC32 || PPC64
+ default "4096" if PARISC && DEBUG_SPINLOCK && !PA20
default "4"

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