linux-kernel - [tip:x86/mm] x86/mm/mtrr: Mark the 'range_new' static variable in mtrr_calc_range_state() as _

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Date:	Fri, 4 Dec 2015 03:49:01 -0800
From:	tip-bot for Rasmus Villemoes <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	hpa@...or.com, toshi.kani@...com, linux@...musvillemoes.dk,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	peterz@...radead.org, tglx@...utronix.de, mingo@...nel.org
Subject: [tip:x86/mm] x86/mm/mtrr: Mark the 'range_new'
  static variable in mtrr_calc_range_state() as __initdata

Commit-ID:  c332813b51cbe807d539bb059b81235abf1e3fdd
Gitweb:     http://git.kernel.org/tip/c332813b51cbe807d539bb059b81235abf1e3fdd
Author:     Rasmus Villemoes <linux@...musvillemoes.dk>
AuthorDate: Tue, 1 Dec 2015 21:44:50 +0100
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Fri, 4 Dec 2015 09:11:28 +0100

x86/mm/mtrr: Mark the 'range_new' static variable in mtrr_calc_range_state() as __initdata

'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@...musvillemoes.dk>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Toshi Kani <toshi.kani@...com>
Link: http://lkml.kernel.org/r/1449002691-20783-1-git-send-email-linux@rasmusvillemoes.dk
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 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 70d7c93..0d98503 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: */
--
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