linux-kernel - [PATCH v2 10/10] mm, cma: use spinlock instead of mutex

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Date:	Thu, 12 Jun 2014 12:21:47 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Michal Nazarewicz <mina86@...a86.com>
Cc:	Minchan Kim <minchan@...nel.org>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Gleb Natapov <gleb@...nel.org>, Alexander Graf <agraf@...e.de>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	kvm@...r.kernel.org, kvm-ppc@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: [PATCH v2 10/10] mm, cma: use spinlock instead of mutex

Currently, we should take the mutex for manipulating bitmap.
This job may be really simple and short so we don't need to sleep
if contended. So I change it to spinlock.

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>

diff --git a/mm/cma.c b/mm/cma.c
index 22a5b23..3085e8c 100644
--- a/mm/cma.c
+++ b/mm/cma.c
@@ -27,6 +27,7 @@
 #include <linux/memblock.h>
 #include <linux/err.h>
 #include <linux/mm.h>
+#include <linux/spinlock.h>
 #include <linux/mutex.h>
 #include <linux/sizes.h>
 #include <linux/slab.h>
@@ -36,7 +37,7 @@ struct cma {
 	unsigned long	count;
 	unsigned long	*bitmap;
 	int order_per_bit; /* Order of pages represented by one bit */
-	struct mutex	lock;
+	spinlock_t	lock;
 };
 
 /*
@@ -72,9 +73,9 @@ static void clear_cma_bitmap(struct cma *cma, unsigned long pfn, int count)
 	bitmapno = (pfn - cma->base_pfn) >> cma->order_per_bit;
 	nr_bits = cma_bitmap_pages_to_bits(cma, count);
 
-	mutex_lock(&cma->lock);
+	spin_lock(&cma->lock);
 	bitmap_clear(cma->bitmap, bitmapno, nr_bits);
-	mutex_unlock(&cma->lock);
+	spin_unlock(&cma->lock);
 }
 
 static int __init cma_activate_area(struct cma *cma)
@@ -112,7 +113,7 @@ static int __init cma_activate_area(struct cma *cma)
 		init_cma_reserved_pageblock(pfn_to_page(base_pfn));
 	} while (--i);
 
-	mutex_init(&cma->lock);
+	spin_lock_init(&cma->lock);
 	return 0;
 
 err:
@@ -261,11 +262,11 @@ struct page *cma_alloc(struct cma *cma, int count, unsigned int align)
 	nr_bits = cma_bitmap_pages_to_bits(cma, count);
 
 	for (;;) {
-		mutex_lock(&cma->lock);
+		spin_lock(&cma->lock);
 		bitmapno = bitmap_find_next_zero_area(cma->bitmap,
 					bitmap_maxno, start, nr_bits, mask);
 		if (bitmapno >= bitmap_maxno) {
-			mutex_unlock(&cma->lock);
+			spin_unlock(&cma->lock);
 			break;
 		}
 		bitmap_set(cma->bitmap, bitmapno, nr_bits);
@@ -274,7 +275,7 @@ struct page *cma_alloc(struct cma *cma, int count, unsigned int align)
 		 * our exclusive use. If the migration fails we will take the
 		 * lock again and unmark it.
 		 */
-		mutex_unlock(&cma->lock);
+		spin_unlock(&cma->lock);
 
 		pfn = cma->base_pfn + (bitmapno << cma->order_per_bit);
 		mutex_lock(&cma_mutex);
-- 
1.7.9.5

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