drivers/iommu/dma-iommu.c | 10 ++++++---- include/linux/dma-map-ops.h | 2 +- include/linux/gfp.h | 2 +- kernel/dma/contiguous.c | 6 +++--- kernel/dma/direct.c | 8 +++++--- kernel/dma/ops_helpers.c | 11 +++++++---- mm/page_alloc.c | 2 +- 7 files changed, 24 insertions(+), 17 deletions(-)
DMA page allocation fallbacks use alloc_pages_node() with get_order(size),
wasting the unused tail for non-power-of-two requests.
Use alloc_pages_exact_nid() and free_pages_exact() so that a buddy
fallback retains only requested pages.
Signed-off-by: Qingfang Deng <qingfang.deng@linux.dev>
---
v2: drop __meminit to fix section mismatch
v1:
https://lore.kernel.org/linux-iommu/20260901085348.53140-1-qingfang.deng@linux.dev/
---
drivers/iommu/dma-iommu.c | 10 ++++++----
include/linux/dma-map-ops.h | 2 +-
include/linux/gfp.h | 2 +-
kernel/dma/contiguous.c | 6 +++---
kernel/dma/direct.c | 8 +++++---
kernel/dma/ops_helpers.c | 11 +++++++----
mm/page_alloc.c | 2 +-
7 files changed, 24 insertions(+), 17 deletions(-)
diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index 58c624513cd4..8f262c83802c 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -1628,10 +1628,12 @@ static void *iommu_dma_alloc_pages(struct device *dev, size_t size,
void *cpu_addr;
page = dma_alloc_contiguous(dev, alloc_size, gfp);
- if (!page)
- page = alloc_pages_node(node, gfp, get_order(alloc_size));
- if (!page)
- return NULL;
+ if (!page) {
+ cpu_addr = alloc_pages_exact_nid(node, alloc_size, gfp);
+ if (!cpu_addr)
+ return NULL;
+ page = virt_to_page(cpu_addr);
+ }
if (!coherent || PageHighMem(page)) {
pgprot_t prot = dma_pgprot(dev, PAGE_KERNEL, attrs);
diff --git a/include/linux/dma-map-ops.h b/include/linux/dma-map-ops.h
index 8fae2b7deb20..3ef3003713a6 100644
--- a/include/linux/dma-map-ops.h
+++ b/include/linux/dma-map-ops.h
@@ -143,7 +143,7 @@ static inline struct page *dma_alloc_contiguous(struct device *dev, size_t size,
static inline void dma_free_contiguous(struct device *dev, struct page *page,
size_t size)
{
- __free_pages(page, get_order(size));
+ free_pages_exact(page_address(page), size);
}
#endif /* CONFIG_DMA_CMA*/
diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index 872bc53f32ec..aa4601805f21 100644
--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h
@@ -329,7 +329,7 @@ void *alloc_pages_exact_noprof(size_t size, gfp_t gfp_mask) __alloc_size(1);
void free_pages_exact(void *virt, size_t size);
-__meminit void *alloc_pages_exact_nid_noprof(int nid, size_t size, gfp_t gfp_mask) __alloc_size(2);
+void *alloc_pages_exact_nid_noprof(int nid, size_t size, gfp_t gfp_mask) __alloc_size(2);
#define alloc_pages_exact_nid(...) \
alloc_hooks(alloc_pages_exact_nid_noprof(__VA_ARGS__))
diff --git a/kernel/dma/contiguous.c b/kernel/dma/contiguous.c
index 66093460584e..90937dc7c627 100644
--- a/kernel/dma/contiguous.c
+++ b/kernel/dma/contiguous.c
@@ -451,8 +451,8 @@ struct page *dma_alloc_contiguous(struct device *dev, size_t size, gfp_t gfp)
*
* 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.
+ * area and true otherwise, this function then does a fallback
+ * free_pages_exact() upon a false-return.
*/
void dma_free_contiguous(struct device *dev, struct page *page, size_t size)
{
@@ -476,7 +476,7 @@ void dma_free_contiguous(struct device *dev, struct page *page, size_t size)
}
/* not in any cma, free from buddy */
- __free_pages(page, get_order(size));
+ free_pages_exact(page_address(page), size);
}
/*
diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
index da665ca22d5c..ea64453d7370 100644
--- a/kernel/dma/direct.c
+++ b/kernel/dma/direct.c
@@ -120,6 +120,7 @@ static struct page *__dma_direct_alloc_pages(struct device *dev, size_t size,
int node = dev_to_node(dev);
struct page *page;
u64 phys_limit;
+ void *va;
WARN_ON_ONCE(!PAGE_ALIGNED(size));
@@ -133,9 +134,9 @@ static struct page *__dma_direct_alloc_pages(struct device *dev, size_t size,
dma_free_contiguous(dev, page, size);
}
- while ((page = alloc_pages_node(node, gfp, get_order(size)))
- && !dma_coherent_ok(dev, page_to_phys(page), size)) {
- __free_pages(page, get_order(size));
+ while ((va = alloc_pages_exact_nid(node, size, gfp)) &&
+ !dma_coherent_ok(dev, virt_to_phys(va), size)) {
+ free_pages_exact(va, size);
if (IS_ENABLED(CONFIG_ZONE_DMA32) &&
phys_limit < DMA_BIT_MASK(64) &&
@@ -146,6 +147,7 @@ static struct page *__dma_direct_alloc_pages(struct device *dev, size_t size,
else
return NULL;
}
+ page = va ? virt_to_page(va) : NULL;
return page;
}
diff --git a/kernel/dma/ops_helpers.c b/kernel/dma/ops_helpers.c
index 6b5f9208d31c..5cdf3f60cf47 100644
--- a/kernel/dma/ops_helpers.c
+++ b/kernel/dma/ops_helpers.c
@@ -67,10 +67,13 @@ struct page *dma_common_alloc_pages(struct device *dev, size_t size,
phys_addr_t phys;
page = dma_alloc_contiguous(dev, size, gfp);
- if (!page)
- page = alloc_pages_node(dev_to_node(dev), gfp, get_order(size));
- if (!page)
- return NULL;
+ if (!page) {
+ void *va = alloc_pages_exact_nid(dev_to_node(dev), size, gfp);
+
+ if (!va)
+ return NULL;
+ page = virt_to_page(va);
+ }
phys = page_to_phys(page);
if (use_dma_iommu(dev))
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index c4dc61ec663e..d3a135dfcdd3 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5637,7 +5637,7 @@ EXPORT_SYMBOL(alloc_pages_exact_noprof);
*
* Return: pointer to the allocated area or %NULL in case of error.
*/
-void * __meminit alloc_pages_exact_nid_noprof(int nid, size_t size, gfp_t gfp_mask)
+void *alloc_pages_exact_nid_noprof(int nid, size_t size, gfp_t gfp_mask)
{
unsigned int order = get_order(size);
struct page *p;
--
2.43.0On 03.09.2026 03:29, Qingfang Deng wrote:
> DMA page allocation fallbacks use alloc_pages_node() with get_order(size),
> wasting the unused tail for non-power-of-two requests.
>
> Use alloc_pages_exact_nid() and free_pages_exact() so that a buddy
> fallback retains only requested pages.
>
> Signed-off-by: Qingfang Deng <qingfang.deng@linux.dev>
Applied to dma-mapping-for-next, thanks!
> ---
> v2: drop __meminit to fix section mismatch
>
> v1:
> https://lore.kernel.org/linux-iommu/20260901085348.53140-1-qingfang.deng@linux.dev/
> ---
> drivers/iommu/dma-iommu.c | 10 ++++++----
> include/linux/dma-map-ops.h | 2 +-
> include/linux/gfp.h | 2 +-
> kernel/dma/contiguous.c | 6 +++---
> kernel/dma/direct.c | 8 +++++---
> kernel/dma/ops_helpers.c | 11 +++++++----
> mm/page_alloc.c | 2 +-
> 7 files changed, 24 insertions(+), 17 deletions(-)
>
> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> index 58c624513cd4..8f262c83802c 100644
> --- a/drivers/iommu/dma-iommu.c
> +++ b/drivers/iommu/dma-iommu.c
> @@ -1628,10 +1628,12 @@ static void *iommu_dma_alloc_pages(struct device *dev, size_t size,
> void *cpu_addr;
>
> page = dma_alloc_contiguous(dev, alloc_size, gfp);
> - if (!page)
> - page = alloc_pages_node(node, gfp, get_order(alloc_size));
> - if (!page)
> - return NULL;
> + if (!page) {
> + cpu_addr = alloc_pages_exact_nid(node, alloc_size, gfp);
> + if (!cpu_addr)
> + return NULL;
> + page = virt_to_page(cpu_addr);
> + }
>
> if (!coherent || PageHighMem(page)) {
> pgprot_t prot = dma_pgprot(dev, PAGE_KERNEL, attrs);
> diff --git a/include/linux/dma-map-ops.h b/include/linux/dma-map-ops.h
> index 8fae2b7deb20..3ef3003713a6 100644
> --- a/include/linux/dma-map-ops.h
> +++ b/include/linux/dma-map-ops.h
> @@ -143,7 +143,7 @@ static inline struct page *dma_alloc_contiguous(struct device *dev, size_t size,
> static inline void dma_free_contiguous(struct device *dev, struct page *page,
> size_t size)
> {
> - __free_pages(page, get_order(size));
> + free_pages_exact(page_address(page), size);
> }
> #endif /* CONFIG_DMA_CMA*/
>
> diff --git a/include/linux/gfp.h b/include/linux/gfp.h
> index 872bc53f32ec..aa4601805f21 100644
> --- a/include/linux/gfp.h
> +++ b/include/linux/gfp.h
> @@ -329,7 +329,7 @@ void *alloc_pages_exact_noprof(size_t size, gfp_t gfp_mask) __alloc_size(1);
>
> void free_pages_exact(void *virt, size_t size);
>
> -__meminit void *alloc_pages_exact_nid_noprof(int nid, size_t size, gfp_t gfp_mask) __alloc_size(2);
> +void *alloc_pages_exact_nid_noprof(int nid, size_t size, gfp_t gfp_mask) __alloc_size(2);
> #define alloc_pages_exact_nid(...) \
> alloc_hooks(alloc_pages_exact_nid_noprof(__VA_ARGS__))
>
> diff --git a/kernel/dma/contiguous.c b/kernel/dma/contiguous.c
> index 66093460584e..90937dc7c627 100644
> --- a/kernel/dma/contiguous.c
> +++ b/kernel/dma/contiguous.c
> @@ -451,8 +451,8 @@ struct page *dma_alloc_contiguous(struct device *dev, size_t size, gfp_t gfp)
> *
> * 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.
> + * area and true otherwise, this function then does a fallback
> + * free_pages_exact() upon a false-return.
> */
> void dma_free_contiguous(struct device *dev, struct page *page, size_t size)
> {
> @@ -476,7 +476,7 @@ void dma_free_contiguous(struct device *dev, struct page *page, size_t size)
> }
>
> /* not in any cma, free from buddy */
> - __free_pages(page, get_order(size));
> + free_pages_exact(page_address(page), size);
> }
>
> /*
> diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> index da665ca22d5c..ea64453d7370 100644
> --- a/kernel/dma/direct.c
> +++ b/kernel/dma/direct.c
> @@ -120,6 +120,7 @@ static struct page *__dma_direct_alloc_pages(struct device *dev, size_t size,
> int node = dev_to_node(dev);
> struct page *page;
> u64 phys_limit;
> + void *va;
>
> WARN_ON_ONCE(!PAGE_ALIGNED(size));
>
> @@ -133,9 +134,9 @@ static struct page *__dma_direct_alloc_pages(struct device *dev, size_t size,
> dma_free_contiguous(dev, page, size);
> }
>
> - while ((page = alloc_pages_node(node, gfp, get_order(size)))
> - && !dma_coherent_ok(dev, page_to_phys(page), size)) {
> - __free_pages(page, get_order(size));
> + while ((va = alloc_pages_exact_nid(node, size, gfp)) &&
> + !dma_coherent_ok(dev, virt_to_phys(va), size)) {
> + free_pages_exact(va, size);
>
> if (IS_ENABLED(CONFIG_ZONE_DMA32) &&
> phys_limit < DMA_BIT_MASK(64) &&
> @@ -146,6 +147,7 @@ static struct page *__dma_direct_alloc_pages(struct device *dev, size_t size,
> else
> return NULL;
> }
> + page = va ? virt_to_page(va) : NULL;
>
> return page;
> }
> diff --git a/kernel/dma/ops_helpers.c b/kernel/dma/ops_helpers.c
> index 6b5f9208d31c..5cdf3f60cf47 100644
> --- a/kernel/dma/ops_helpers.c
> +++ b/kernel/dma/ops_helpers.c
> @@ -67,10 +67,13 @@ struct page *dma_common_alloc_pages(struct device *dev, size_t size,
> phys_addr_t phys;
>
> page = dma_alloc_contiguous(dev, size, gfp);
> - if (!page)
> - page = alloc_pages_node(dev_to_node(dev), gfp, get_order(size));
> - if (!page)
> - return NULL;
> + if (!page) {
> + void *va = alloc_pages_exact_nid(dev_to_node(dev), size, gfp);
> +
> + if (!va)
> + return NULL;
> + page = virt_to_page(va);
> + }
>
> phys = page_to_phys(page);
> if (use_dma_iommu(dev))
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index c4dc61ec663e..d3a135dfcdd3 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5637,7 +5637,7 @@ EXPORT_SYMBOL(alloc_pages_exact_noprof);
> *
> * Return: pointer to the allocated area or %NULL in case of error.
> */
> -void * __meminit alloc_pages_exact_nid_noprof(int nid, size_t size, gfp_t gfp_mask)
> +void *alloc_pages_exact_nid_noprof(int nid, size_t size, gfp_t gfp_mask)
> {
> unsigned int order = get_order(size);
> struct page *p;
Best regards
--
Marek Szyprowski, PhD
Samsung R&D Institute Poland
© 2016 - 2026 Red Hat, Inc.