linux-kernel - [PATCH] arm: dma: Drop GFP_COMP for DMA memory allocations

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Message-Id: <1320442539-7753-1-git-send-email-swarren@nvidia.com>
Date:	Fri,  4 Nov 2011 15:35:39 -0600
From:	Stephen Warren <swarren@...dia.com>
To:	Russell King <linux@....linux.org.uk>
Cc:	Jon Medhurst <tixy@...t.co.uk>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Sumit Bhattacharya <sumitb@...dia.com>,
	Stephen Warren <swarren@...dia.com>
Subject: [PATCH] arm: dma:  Drop GFP_COMP for DMA memory allocations

From: Sumit Bhattacharya <sumitb@...dia.com>

dma_alloc_coherent wants to split pages after allocation in order to
reduce the memory footprint. This does not work well with GFP_COMP
pages, so drop this flag before allocation.

This patch is ported from arch/avr32
(commit 3611553ef985ef7c5863c8a94641738addd04cff).

Signed-off-by: Sumit Bhattacharya <sumitb@...dia.com>
Tested-by: Varun Colbert <vcolbert@...dia.com>
[swarren: s/HUGETLB_PAGE/HUGETLBFS/ in comment, minor comment cleanup]
Signed-off-by: Stephen Warren <swarren@...dia.com>
---
 arch/arm/mm/dma-mapping.c |    9 +++++++++
 1 files changed, 9 insertions(+), 0 deletions(-)

diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
index e4e7f6c..68d64b4 100644
--- a/arch/arm/mm/dma-mapping.c
+++ b/arch/arm/mm/dma-mapping.c
@@ -332,6 +332,15 @@ __dma_alloc(struct device *dev, size_t size, dma_addr_t *handle, gfp_t gfp,
 	struct page *page;
 	void *addr;
 
+	/*
+	 * Following is a work-around (a.k.a. hack) to prevent pages
+	 * with __GFP_COMP being passed to split_page() which cannot
+	 * handle them.  The real problem is that this flag probably
+	 * should be 0 on ARM as it is not supported on this
+	 * platform; see CONFIG_HUGETLBFS.
+	 */
+	gfp &= ~(__GFP_COMP);
+
 	*handle = ~0;
 	size = PAGE_ALIGN(size);
 
-- 
1.7.0.4

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