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[PATCH v2] x86, mtrr: mark range_new in mtrr_calc_range_state() as __initdata

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range_new doesn't seem to be used after init. It is only passed to
memset, sum_ranges, memcmp and x86_get_mtrr_mem_range, the latter of
which also only passes it on to various *range* library functions. So
mark it __initdata to free up an extra page after init.

Its contents are wiped at every call to mtrr_calc_range_state(), so it
being static is not about preserving state between calls, but simply
to avoid a 4k+ stack frame. While there, add a comment explaining this
and why it's safe.

We could also mark nr_range_new as __initdata, but since it's just a
single int and also doesn't carry state between calls (it is
unconditionally assigned to before it is read), we might as well make
it an ordinary automatic variable.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
---
Something like this, perhaps?

v2: Add comment on range_new, per Ingo.

 arch/x86/kernel/cpu/mtrr/cleanup.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/mtrr/cleanup.c b/arch/x86/kernel/cpu/mtrr/cleanup.c
index 70d7c93f4550..0d98503c2245 100644
--- a/arch/x86/kernel/cpu/mtrr/cleanup.c
+++ b/arch/x86/kernel/cpu/mtrr/cleanup.c
@@ -593,9 +593,16 @@ mtrr_calc_range_state(u64 chunk_size, u64 gran_size,
 		      unsigned long x_remove_base,
 		      unsigned long x_remove_size, int i)
 {
-	static struct range range_new[RANGE_NUM];
+	/*
+	 * range_new should really be an automatic variable, but
+	 * putting 4096 bytes on the stack is frowned upon, to put it
+	 * mildly. It is safe to make it a static __initdata variable,
+	 * since mtrr_calc_range_state is only called during init and
+	 * there's no way it will call itself recursively.
+	 */
+	static struct range range_new[RANGE_NUM] __initdata;
 	unsigned long range_sums_new;
-	static int nr_range_new;
+	int nr_range_new;
 	int num_reg;
 
 	/* Convert ranges to var ranges state: */
-- 
2.6.1

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Re: [PATCH] x86, mtrr: mark range_new in mtrr_calc_range_state() as __initdata Rasmus Villemoes <linux@rasmusvillemoes.dk> - 2015-12-01 13:00 +0100
  Re: [PATCH] x86, mtrr: mark range_new in mtrr_calc_range_state() as  __initdata Ingo Molnar <mingo@kernel.org> - 2015-12-01 17:20 +0100
    [PATCH v2] x86, mtrr: mark range_new in mtrr_calc_range_state() as __initdata Rasmus Villemoes <linux@rasmusvillemoes.dk> - 2015-12-01 21:50 +0100
      [tip:x86/mm] x86/mm/mtrr: Mark the 'range_new'   static variable in mtrr_calc_range_state() as __initdata tip-bot for Rasmus Villemoes <tipbot@zytor.com> - 2015-12-04 13:00 +0100

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