linux-kernel - [PATCH v2] x86, mtrr: mark range_new in mtrr_calc_range_state() as _

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Date:	Tue,  1 Dec 2015 21:44:50 +0100
From:	Rasmus Villemoes <linux@...musvillemoes.dk>
To:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org
Cc:	Toshi Kani <toshi.kani@...com>, Borislav Petkov <bp@...en8.de>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	linux-kernel@...r.kernel.org
Subject: [PATCH v2] x86, mtrr: mark range_new 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>
---
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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