[PATCH v3 1/2] dma-contiguous: Abstract dma_{alloc, free}_contiguous()

Nicolin Chen
2019-05-24T04:08:10Z

Both dma_alloc_from_contiguous() and dma_release_from_contiguous()
are very simply implemented, but requiring callers to pass certain
parameters like count and align, and taking a boolean parameter to
check __GFP_NOWARN in the allocation flags. So every function call
duplicates similar work:
/* A piece of example */
unsigned long order = get_order(size);
size_t count = size >> PAGE_SHIFT;
page = dma_alloc_from_contiguous(dev, count, order, gfp & __GFP_NOWARN);
[...]
dma_release_from_contiguous(dev, page, size >> PAGE_SHIFT);

Additionally, as CMA can be used only in the context which permits
sleeping, most of callers do a gfpflags_allow_blocking() check and
a corresponding fallback allocation of normal pages upon any false
result:
/* A piece of example */
if (gfpflags_allow_blocking(flag))
page = dma_alloc_from_contiguous();
if (!page)
page = alloc_pages();
[...]
if (!dma_release_from_contiguous(dev, page, count))
__free_pages(page, get_order(size));

So this patch simplifies those function calls by abstracting these
operations into the two new functions: dma_{alloc,free}_contiguous.

As some callers of dma_{alloc,release}_from_contiguous() might be
complicated, this patch just implements these two new functions to
kernel/dma/direct.c only as an initial step.

Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Nicolin Chen <nicoleotsuka@gmail.com>
---
Changelog
v2->v3:
* Added missing "static inline" in header file to fix build error.
v1->v2:
* Added new functions beside the old ones so we can replace callers
one by one later.
* Applied new functions to dma/direct.c only, because it's the best
example caller to apply and should be safe with the new functions.

include/linux/dma-contiguous.h | 11 ++++++++
kernel/dma/contiguous.c | 48 ++++++++++++++++++++++++++++++++++
kernel/dma/direct.c | 24 +++--------------
3 files changed, 63 insertions(+), 20 deletions(-)

diff --git a/include/linux/dma-contiguous.h b/include/linux/dma-contiguous.h
index f247e8aa5e3d..00a370c1c140 100644
--- a/include/linux/dma-contiguous.h
+++ b/include/linux/dma-contiguous.h
@@ -115,6 +115,8 @@ struct page *dma_alloc_from_contiguous(struct device *dev, size_t count,
unsigned int order, bool no_warn);
bool dma_release_from_contiguous(struct device *dev, struct page *pages,
int count);
+struct page *dma_alloc_contiguous(struct device *dev, size_t size, gfp_t gfp);
+void dma_free_contiguous(struct device *dev, struct page *page, size_t size);

#else

@@ -157,6 +159,15 @@ bool dma_release_from_contiguous(struct device *dev, struct page *pages,
return false;
}

+static inline
+struct page *dma_alloc_contiguous(struct device *dev, size_t size, gfp_t gfp)
+{
+ return NULL;
+}
+
+static inline
+void dma_free_contiguous(struct device *dev, struct page *page, size_t size) { }
+
#endif

#endif
diff --git a/kernel/dma/contiguous.c b/kernel/dma/contiguous.c
index b2a87905846d..21f39a6cb04f 100644
--- a/kernel/dma/contiguous.c
+++ b/kernel/dma/contiguous.c
@@ -214,6 +214,54 @@ bool dma_release_from_contiguous(struct device *dev, struct page *pages,
return cma_release(dev_get_cma_area(dev), pages, count);
}

+/**
+ * dma_alloc_contiguous() - allocate contiguous pages
+ * @dev: Pointer to device for which the allocation is performed.
+ * @size: Requested allocation size.
+ * @gfp: Allocation flags.
+ *
+ * This function allocates contiguous memory buffer for specified device. It
+ * first tries to use device specific contiguous memory area if available or
+ * the default global one, then tries a fallback allocation of normal pages.
+ */
+struct page *dma_alloc_contiguous(struct device *dev, size_t size, gfp_t gfp)
+{
+ int node = dev ? dev_to_node(dev) : NUMA_NO_NODE;
+ size_t count = PAGE_ALIGN(size) >> PAGE_SHIFT;
+ size_t align = get_order(PAGE_ALIGN(size));
+ struct cma *cma = dev_get_cma_area(dev);
+ struct page *page = NULL;
+
+ /* CMA can be used only in the context which permits sleeping */
+ if (cma && gfpflags_allow_blocking(gfp)) {
+ align = min_t(size_t, align, CONFIG_CMA_ALIGNMENT);
+ page = cma_alloc(cma, count, align, gfp & __GFP_NOWARN);
+ }
+
+ /* Fallback allocation of normal pages */
+ if (!page)
+ page = alloc_pages_node(node, gfp, align);
+
+ return page;
+}
+
+/**
+ * dma_free_contiguous() - release allocated pages
+ * @dev: Pointer to device for which the pages were allocated.
+ * @page: Pointer to the allocated pages.
+ * @size: Size of allocated pages.
+ *
+ * This function releases memory allocated by dma_alloc_contiguous(). As the
+ * cma_release returns false when provided pages do not belong to contiguous
+ * area and true otherwise, this function then does a fallback __free_pages()
+ * upon a false-return.
+ */
+void dma_free_contiguous(struct device *dev, struct page *page, size_t size)
+{
+ if (!cma_release(dev_get_cma_area(dev), page, size >> PAGE_SHIFT))
+ __free_pages(page, get_order(size));
+}
+
/*
* Support for reserved memory regions defined in device tree
*/
diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
index 2c2772e9702a..0816c1e8b05a 100644
--- a/kernel/dma/direct.c
+++ b/kernel/dma/direct.c
@@ -96,8 +96,6 @@ static bool dma_coherent_ok(struct device *dev, phys_addr_t phys, size_t size)
struct page *__dma_direct_alloc_pages(struct device *dev, size_t size,
dma_addr_t *dma_handle, gfp_t gfp, unsigned long attrs)
{
- unsigned int count = PAGE_ALIGN(size) >> PAGE_SHIFT;
- int page_order = get_order(size);
struct page *page = NULL;
u64 phys_mask;

@@ -109,20 +107,9 @@ struct page *__dma_direct_alloc_pages(struct device *dev, size_t size,
gfp |= __dma_direct_optimal_gfp_mask(dev, dev->coherent_dma_mask,
&phys_mask);
again:
- /* CMA can be used only in the context which permits sleeping */
- if (gfpflags_allow_blocking(gfp)) {
- page = dma_alloc_from_contiguous(dev, count, page_order,
- gfp & __GFP_NOWARN);
- if (page && !dma_coherent_ok(dev, page_to_phys(page), size)) {
- dma_release_from_contiguous(dev, page, count);
- page = NULL;
- }
- }
- if (!page)
- page = alloc_pages_node(dev_to_node(dev), gfp, page_order);
-
+ page = dma_alloc_contiguous(dev, size, gfp);
if (page && !dma_coherent_ok(dev, page_to_phys(page), size)) {
- __free_pages(page, page_order);
+ dma_free_contiguous(dev, page, size);
page = NULL;

if (IS_ENABLED(CONFIG_ZONE_DMA32) &&
@@ -154,7 +141,7 @@ void *dma_direct_alloc_pages(struct device *dev, size_t size,
if (PageHighMem(page)) {
/*
* Depending on the cma= arguments and per-arch setup
- * dma_alloc_from_contiguous could return highmem pages.
+ * dma_alloc_contiguous could return highmem pages.
* Without remapping there is no way to return them here,
* so log an error and fail.
*/
@@ -176,10 +163,7 @@ void *dma_direct_alloc_pages(struct device *dev, size_t size,

void __dma_direct_free_pages(struct device *dev, size_t size, struct page *page)
{
- unsigned int count = PAGE_ALIGN(size) >> PAGE_SHIFT;
-
- if (!dma_release_from_contiguous(dev, page, count))
- __free_pages(page, get_order(size));
+ dma_free_contiguous(dev, page, size);
}

void dma_direct_free_pages(struct device *dev, size_t size, void *cpu_addr,
--
2.17.1