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Subject[PATCH v4] iommu/dma: Use NUMA aware memory allocations in __iommu_dma_alloc_pages()
Date
From: Ganapatrao Kulkarni <ganapatrao.kulkarni@cavium.com>

Change function __iommu_dma_alloc_pages() to allocate pages for DMA from
respective device NUMA node. The ternary operator which would be for
alloc_pages_node() is tidied along with this.

The motivation for this change is to have a policy for page allocation
consistent with direct DMA mapping, which attempts to allocate pages local
to the device, as mentioned in [1].

In addition, for certain workloads it has been observed a marginal
performance improvement. The patch caused an observation of 0.9% average
throughput improvement for running tcrypt with HiSilicon crypto engine.

We also include a modification to use kvzalloc() for kzalloc()/vzalloc()
combination.

[1] https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1692998.html

Signed-off-by: Ganapatrao Kulkarni <ganapatrao.kulkarni@cavium.com>
[JPG: Added kvzalloc(), drop pages ** being device local, remove ternary operator, update message]
Signed-off-by: John Garry <john.garry@huawei.com>
---
Difference:
v1->v2:
- Add Ganapatrao's tag and change author

v2->v3:
- removed ternary operator
- stopped making pages ** allocation local to device

v3->v4:
- Update commit message to include motivation for patch, including
headline performance improvement for test.

Some notes:
This patch was originally posted by Ganapatrao in [2].

However, after initial review, it was never reposted (due to lack of
cycles, I think). In addition, the functionality in its sibling patches
were merged through patches, as mentioned in [2]; this also refers to a
discussion on device local allocations vs CPU local allocations for DMA
pool, and which is better [1].

However, as mentioned in [1], dma_alloc_coherent() uses the locality
information from the device - as in direct DMA - so this patch is just
applying this same policy.

And from some testing, mentioned in commit message, shows marginal
improvement.

[2] https://lore.kernel.org/patchwork/patch/833004/
[3] https://lkml.org/lkml/2018/8/22/391

diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index d1b0475..4afb1a8 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -449,20 +449,17 @@ static void __iommu_dma_free_pages(struct page **pages, int count)
kvfree(pages);
}

-static struct page **__iommu_dma_alloc_pages(unsigned int count,
- unsigned long order_mask, gfp_t gfp)
+static struct page **__iommu_dma_alloc_pages(struct device *dev,
+ unsigned int count, unsigned long order_mask, gfp_t gfp)
{
struct page **pages;
- unsigned int i = 0, array_size = count * sizeof(*pages);
+ unsigned int i = 0, nid = dev_to_node(dev);

order_mask &= (2U << MAX_ORDER) - 1;
if (!order_mask)
return NULL;

- if (array_size <= PAGE_SIZE)
- pages = kzalloc(array_size, GFP_KERNEL);
- else
- pages = vzalloc(array_size);
+ pages = kvzalloc(count * sizeof(*pages), GFP_KERNEL);
if (!pages)
return NULL;

@@ -481,10 +478,12 @@ static struct page **__iommu_dma_alloc_pages(unsigned int count,
for (order_mask &= (2U << __fls(count)) - 1;
order_mask; order_mask &= ~order_size) {
unsigned int order = __fls(order_mask);
+ gfp_t alloc_flags = gfp;

order_size = 1U << order;
- page = alloc_pages((order_mask - order_size) ?
- gfp | __GFP_NORETRY : gfp, order);
+ if (order_mask > order_size)
+ alloc_flags |= __GFP_NORETRY;
+ page = alloc_pages_node(nid, alloc_flags, order);
if (!page)
continue;
if (!order)
@@ -569,7 +568,8 @@ struct page **iommu_dma_alloc(struct device *dev, size_t size, gfp_t gfp,
alloc_sizes = min_size;

count = PAGE_ALIGN(size) >> PAGE_SHIFT;
- pages = __iommu_dma_alloc_pages(count, alloc_sizes >> PAGE_SHIFT, gfp);
+ pages = __iommu_dma_alloc_pages(dev, count, alloc_sizes >> PAGE_SHIFT,
+ gfp);
if (!pages)
return NULL;

--
1.9.1
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