On Mon, 06 Mar 2017 09:07:48 +0530
"Aneesh Kumar K.V" [off-list ref] wrote:

"Aneesh Kumar K.V" [off-list ref] writes:
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quoted

Michal Such=C3=A1nek [off-list ref] writes:
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Hello,

On Sun, 19 Feb 2017 15:37:15 +0530
"Aneesh Kumar K.V" [off-list ref] wrote:
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We update the hash linux page table layout such that we can
support 512TB. But we limit the TASK_SIZE to 128TB. We can switch
to 128TB by default without conditional because that is the max
virtual address supported by other architectures. We will later
add a mechanism to on-demand increase the application's effective
address range to 512TB.
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Having the page table layout changed to accommodate 512TB  makes
testing large memory configuration easier with less code changes
to kernel
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Signed-off-by: Aneesh Kumar K.V
[off-list ref] =20

....
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index b64daf124fee..c7ca70dc3ba5 100644 =20

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--- a/arch/powerpc/kernel/paca.c
+++ b/arch/powerpc/kernel/paca.c

@@ -253,8 +253,15 @@ void copy_mm_to_paca(struct mm_struct *mm)
 	get_paca()->mm_ctx_id =3D context->id;
 #ifdef CONFIG_PPC_MM_SLICES
 	get_paca()->mm_ctx_low_slices_psize =3D

context->low_slices_psize;
+	/*
+	 * We support upto 128TB for now. Hence copy only 128/2
bytes.
+	 * Later when we support tasks with different max
effective
+	 * address, we can optimize this based on mm->task_size.
+	 */
+	BUILD_BUG_ON(TASK_SIZE_USER64 !=3D TASK_SIZE_128TB); =20

Can this be handled by KConfig?
Above I see  =20

I am reworking the series so that we depend on mm->task_size. Will
send a new version soon.


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+#ifdef CONFIG_PPC_BOOK3S_64
+#define TASK_SIZE_USER64 TASK_SIZE_128TB
+#else
+#define TASK_SIZE_USER64 TASK_SIZE_64TB
+#endif =20

and  =20

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#ifdef CONFIG_PPC_MM_SLICES
ILD_BUG_ON(TASK_SIZE_USER64 !=3D TASK_SIZE_128TB) =20

which boils down to
#ifndef CONFIG_PPC_BOOK3S_64
#ifdef CONFIG_PPC_MM_SLICES
#error TASK_SIZE_USER64 !=3D TASK_SIZE_128TB

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 	memcpy(&get_paca()->mm_ctx_high_slices_psize,
-	       &context->high_slices_psize, SLICE_ARRAY_SIZE);
+	       &context->high_slices_psize, TASK_SIZE_128TB >>
41); =20

Can we avoid magic numbers, please?
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Since array is 4 bytes per each TB which is documented else where. =20

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4 bits per teach TB.
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It is certainly nicer to have a macro for it. You can then see what the
number is from the macro name or grep it and find the definition and
the explanation.

Thanks

Michal