linux-kernel - [PATCH 1/2] kfifo: round up the fifo size power of 2

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Message-Id: <1351238218-22648-1-git-send-email-yuanhan.liu@linux.intel.com>
Date:	Fri, 26 Oct 2012 15:56:57 +0800
From:	Yuanhan Liu <yuanhan.liu@...ux.intel.com>
To:	linux-kernel@...r.kernel.org
Cc:	Yuanhan Liu <yuanhan.liu@...ux.intel.com>,
	Stefani Seibold <stefani@...bold.net>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH 1/2] kfifo: round up the fifo size power of 2

Say, if we want to allocate a filo with size of 6 bytes, it would be safer
to allocate 8 bytes instead of 4 bytes.
----
I know it works with rounddown_pow_of_two as well, since size is maintained
in the kfifo internal part. But, I'm quite curious why Stefani chose
rounddown_pow_of_two. To reduce memory?

Thanks,
Yuanhan Liu
-----

Cc: Stefani Seibold <stefani@...bold.net>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Yuanhan Liu <yuanhan.liu@...ux.intel.com>
---
 kernel/kfifo.c |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/kfifo.c b/kernel/kfifo.c
index 59dcf5b..0f78378 100644
--- a/kernel/kfifo.c
+++ b/kernel/kfifo.c
@@ -39,11 +39,11 @@ int __kfifo_alloc(struct __kfifo *fifo, unsigned int size,
 		size_t esize, gfp_t gfp_mask)
 {
 	/*
-	 * round down to the next power of 2, since our 'let the indices
+	 * round up to the next power of 2, since our 'let the indices
 	 * wrap' technique works only in this case.
 	 */
 	if (!is_power_of_2(size))
-		size = rounddown_pow_of_two(size);
+		size = roundup_pow_of_two(size);
 
 	fifo->in = 0;
 	fifo->out = 0;
@@ -84,7 +84,7 @@ int __kfifo_init(struct __kfifo *fifo, void *buffer,
 	size /= esize;
 
 	if (!is_power_of_2(size))
-		size = rounddown_pow_of_two(size);
+		size = roundup_pow_of_two(size);
 
 	fifo->in = 0;
 	fifo->out = 0;
-- 
1.7.7.6

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