linux-kernel - [PATCH 2/2] intel-iommu: don't unnecessarily call dma_alloc_from

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Date:	Mon, 29 Sep 2014 00:52:04 +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>,
	Peter Hurley <peter@...leysoftware.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>,
	Yinghai Lu <yinghai@...nel.org>, x86@...nel.org,
	iommu@...ts.linux-foundation.org
Subject: [PATCH 2/2] intel-iommu: don't unnecessarily call dma_alloc_from_contiguous()

If CONFIG_DMA_CMA is enabled, intel_alloc_coherent() tries to allocate
memory region by dma_alloc_from_contiguous() before trying to use
alloc_pages().

This wastes CMA region by small DMA-coherent buffers which can be
allocated by alloc_pages().  And it also causes performance degradation,
as this is trying to drive _all_ dma mapping allocations through a
_very_ small window, reported by Peter Hurley.

This fixes it by trying to allocate by alloc_pages() first in
intel_alloc_coherent() as dma_alloc_from_contiguous should be called
only for huge allocation.

Signed-off-by: Akinobu Mita <akinobu.mita@...il.com>
Reported-by: Peter Hurley <peter@...leysoftware.com>
Cc: Peter Hurley <peter@...leysoftware.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: Yinghai Lu <yinghai@...nel.org>
Cc: x86@...nel.org
Cc: iommu@...ts.linux-foundation.org
---
 drivers/iommu/intel-iommu.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
index 3441615..f9794fa 100644
--- a/drivers/iommu/intel-iommu.c
+++ b/drivers/iommu/intel-iommu.c
@@ -3250,7 +3250,8 @@ static void *intel_alloc_coherent(struct device *dev, size_t size,
 			flags |= GFP_DMA32;
 	}
 
-	if (flags & __GFP_WAIT) {
+	page = alloc_pages(flags | __GFP_NOWARN, order);
+	if (!page && (flags & __GFP_WAIT)) {
 		unsigned int count = size >> PAGE_SHIFT;
 
 		page = dma_alloc_from_contiguous(dev, count, order);
@@ -3261,10 +3262,10 @@ static void *intel_alloc_coherent(struct device *dev, size_t size,
 		}
 	}
 
-	if (!page)
-		page = alloc_pages(flags, order);
-	if (!page)
+	if (!page) {
+		warn_alloc_failed(flags, order, NULL);
 		return NULL;
+	}
 	memset(page_address(page), 0, size);
 
 	*dma_handle = __intel_map_single(dev, page_to_phys(page), size,
-- 
1.9.1

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