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[PATCH] 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?

Well, arm26 manages it by returning a pte_t pointer cast to a struct page
pointer, harumph, then compensating in its pmd_populate.  But arm26 is never
SMP, so it's not a problem for split ptlock either.

And the PA-RISC situation has been recently improved: CONFIG_PA20 works
without the 16-byte alignment which inflated its spinlock_t.  But the current
union of spinlock_t with private does make the 7xxx struct page significantly
larger, even without debug, so disable its split ptlock.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Hugh Dickins 2005-11-23 13:37:37 -08:00 committed by Linus Torvalds
parent c101e77301
commit 7b6ac9dffe
1 changed files with 2 additions and 4 deletions
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mm/Kconfig
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@ -125,12 +125,10 @@ comment "Memory hotplug is currently incompatible with Software Suspend"
# 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 spinlock_t would enlarge struct page from 32 to 44 bytes.
#
config SPLIT_PTLOCK_CPUS
int
default "4096" if ARM && !CPU_CACHE_VIPT
default "4096" if PARISC && DEBUG_SPINLOCK && !64BIT
default "4096" if ARM26 || SPARC32 || PPC64
default "4096" if PARISC && !PA20
default "4"