Dave Hansen <dave.hansen@xxxxxxxxx> writes:
> On 04/08/2014 06:32 PM, Madhavan Srinivasan wrote:
>>> > In mm/Kconfig, put
>>> >
>>> > config FAULT_AROUND_ORDER
>>> > int
>>> > default 1234 if POWERPC
>>> > default 4
>>> >
>>> > The way you have it now, every single architecture that needs to enable
>>> > this has to go put that in their Kconfig. That's madness. This way,
>> I though about it and decided not to do this way because, in future,
>> sub platforms of the architecture may decide to change the values. Also,
>> adding an if line for each architecture with different sub platforms
>> oring to it will look messy.
>
> I'm not sure why I'm trying here any more. You do seem quite content to
> add as much cruft to ppc and every other architecture as possible. If
> your theoretical scenario pops up, you simply do this in ppc:
>
> config ARCH_FAULT_AROUND_ORDER
> int
> default 999
> default 888 if OTHER_SILLY_POWERPC_SUBARCH
>
> But *ONLY* in the architectures that care about doing that stuff. You
> leave every other architecture on the planet alone. Then, in mm/Kconfig:
>
> config FAULT_AROUND_ORDER
> int
> default ARCH_FAULT_AROUND_ORDER if ARCH_FAULT_AROUND_ORDER
> default 4
>
> Your way still requires going and individually touching every single
> architecture's Kconfig that wants to enable fault around. That's not an
> acceptable solution.
Why bother with Kconfig at all? It seems like a weird indirection.
And talking about future tuning seems like a separate issue, if and when
someone does the work. For the moment, let's keep it simple (as below).
If you really want Kconfig, then just go straight from
ARCH_FAULT_AROUND_ORDER, ie:
#ifdef CONFIG_ARCH_FAULT_AROUND_ORDER
#define FAULT_AROUND_ORDER CONFIG_ARCH_FAULT_AROUND_ORDER
#else
#define FAULT_AROUND_ORDER 4
#endif
Then powerpc's Kconfig defines CONFIG_ARCH_FAULT_AROUND_ORDER, and
we're done.
Cheers,
Rusty.
diff --git a/arch/powerpc/include/asm/page.h b/arch/powerpc/include/asm/page.h
index 32e4e212b9c1..b519c5c53cfc 100644
--- a/arch/powerpc/include/asm/page.h
+++ b/arch/powerpc/include/asm/page.h
@@ -412,4 +412,7 @@ typedef struct page *pgtable_t;
#include <asm-generic/memory_model.h>
#endif /* __ASSEMBLY__ */
+/* Measured on a 4 socket Power7 system (128 Threads and 128GB memory) */
+#define FAULT_AROUND_ORDER 3
+
#endif /* _ASM_POWERPC_PAGE_H */
diff --git a/mm/memory.c b/mm/memory.c
index d0f0bef3be48..9aa47e9ec7ba 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3382,7 +3382,10 @@ void do_set_pte(struct vm_area_struct *vma, unsigned long address,
update_mmu_cache(vma, address, pte);
}
+/* Archs can override, but this seems to work for x86. */
+#ifndef FAULT_AROUND_ORDER
#define FAULT_AROUND_ORDER 4
+#endif
#ifdef CONFIG_DEBUG_FS
static unsigned int fault_around_order = FAULT_AROUND_ORDER;
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