linux-kernel - [PATCH -mm 2/2] x86: avoid duplicated memset in dma_generic_alloc

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Date:	Sun, 20 Apr 2014 21:39:47 +0900
From:	Akinobu Mita <akinobu.mita@...il.com>
To:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org
Cc:	Akinobu Mita <akinobu.mita@...il.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Don Dutile <ddutile@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Andi Kleen <andi@...stfloor.org>,
	x86@...nel.org, iommu@...ts.linux-foundation.org
Subject: [PATCH -mm 2/2] x86: avoid duplicated memset in dma_generic_alloc_coherent()

This patch fixes duplicated memset that is introduced by the patch
x86-make-dma_alloc_coherent-return-zeroed-memory-if-cma-is-enabled.patch
in -mm tree, and this change should be folded into it.

If dma_generic_alloc_coherent() is called with __GFP_ZERO, it does a
duplicated memset to the memory area allocated by alloc_pages_node()
with __GFP_ZERO.  This change fixes that inefficiency by clearing
__GFP_ZERO bit in gfp flages before calling alloc_pages_node().  Note
that dma_generic_alloc_coherent() always returns zeroed memory.

Signed-off-by: Akinobu Mita <akinobu.mita@...il.com>
Cc: Marek Szyprowski <m.szyprowski@...sung.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc: David Woodhouse <dwmw2@...radead.org>
Cc: Don Dutile <ddutile@...hat.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: Andi Kleen <andi@...stfloor.org>
Cc: x86@...nel.org
Cc: iommu@...ts.linux-foundation.org
---
 arch/x86/kernel/pci-dma.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c
index f15bf8d..a25e202 100644
--- a/arch/x86/kernel/pci-dma.c
+++ b/arch/x86/kernel/pci-dma.c
@@ -97,6 +97,7 @@ void *dma_generic_alloc_coherent(struct device *dev, size_t size,
 
 	dma_mask = dma_alloc_coherent_mask(dev, flag);
 
+	flag &= ~__GFP_ZERO;
 again:
 	page = NULL;
 	/* CMA can be used only in the context which permits sleeping */
-- 
1.8.3.2

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