Ganapatrao Kulkarni has put some effort on making arm-smmu-v3 use local
memory to save command queues[1]. I also did similar job in patch
"iommu/arm-smmu-v3: allocate the memory of queues in local numa node"
[2] while not realizing Ganapatrao has done that before.
But it seems it is much better to make dma_alloc_coherent() to be
inherently NUMA-aware on NUMA-capable systems.
Right now, smmu is using dma_alloc_coherent() to get memory to save queues
and tables. Typically, on ARM64 server, there is a default CMA located at
node0, which could be far away from node2, node3 etc.
Saving queues and tables remotely will increase the latency of ARM SMMU
significantly. For example, when SMMU is at node2 and the default global
CMA is at node0, after sending a CMD_SYNC in an empty command queue, we
have to wait more than 550ns for the completion of the command CMD_SYNC.
However, if we save them locally, we only need to wait for 240ns.
with per-numa CMA, smmu will get memory from local numa node to save command
queues and page tables. that means dma_unmap latency will be shrunk much.
Meanwhile, when iommu.passthrough is on, device drivers which call dma_
alloc_coherent() will also get local memory and avoid the travel between
numa nodes.
[1] https://lists.linuxfoundation.org/pipermail/iommu/2017-October/024455.html
[2] https://www.spinics.net/lists/iommu/msg44767.html
-v7:
* add Will's acked-by for the change in arch/arm64
* some cleanup with respect to Will's comments
* add patch 3/3 to remove the hardcode of defining the size of cma name.
this patch requires some header file change in include/linux
-v6:
* rebase on top of 5.9-rc1
* doc cleanup
-v5:
refine code according to Christoph Hellwig's comments
* remove Kconfig option for pernuma cma size;
* add Kconfig option for pernuma cma enable;
* code cleanup like line over 80 char
I haven't removed the cma NULL check code in cma_alloc() as it requires
a bundle of other changes. So I prefer to handle this issue separately.
-v4:
* rebase on top of Christoph Hellwig's patch:
[PATCH v2] dma-contiguous: cleanup dma_alloc_contiguous
https://lore.kernel.org/linux-iommu/[email protected]/
* cleanup according to Christoph's comment
* rebase on top of linux-next to avoid arch/arm64 conflicts
* reserve cma by checking N_MEMORY rather than N_ONLINE
-v3:
* move to use page_to_nid() while freeing cma with respect to Robin's
comment, but this will only work after applying my below patch:
"mm/cma.c: use exact_nid true to fix possible per-numa cma leak"
https://marc.info/?l=linux-mm&m=159333034726647&w=2
* handle the case count <= 1 more properly according to Robin's
comment;
* add pernuma_cma parameter to support dynamic setting of per-numa
cma size;
ideally we can leverage the CMA_SIZE_MBYTES, CMA_SIZE_PERCENTAGE and
"cma=" kernel parameter and avoid a new paramter separately for per-
numa cma. Practically, it is really too complicated considering the
below problems:
(1) if we leverage the size of default numa for per-numa, we have to
avoid creating two cma with same size in node0 since default cma is
probably on node0.
(2) default cma can consider the address limitation for old devices
while per-numa cma doesn't support GFP_DMA and GFP_DMA32. all
allocations with limitation flags will fallback to default one.
(3) hard to apply CMA_SIZE_PERCENTAGE to per-numa. it is hard to
decide if the percentage should apply to the whole memory size
or only apply to the memory size of a specific numa node.
(4) default cma size has CMA_SIZE_SEL_MIN and CMA_SIZE_SEL_MAX, it
makes things even more complicated to per-numa cma.
I haven't figured out a good way to leverage the size of default cma
for per-numa cma. it seems a separate parameter for per-numa could
make life easier.
* move dma_pernuma_cma_reserve() after hugetlb_cma_reserve() to
reuse the comment before hugetlb_cma_reserve() with respect to
Robin's comment
-v2:
* fix some issues reported by kernel test robot
* fallback to default cma while allocation fails in per-numa cma
free memory properly
Barry Song (3):
dma-contiguous: provide the ability to reserve per-numa CMA
arm64: mm: reserve per-numa CMA to localize coherent dma buffers
mm: cma: use CMA_MAX_NAME to define the length of cma name array
.../admin-guide/kernel-parameters.txt | 11 ++
arch/arm64/mm/init.c | 2 +
include/linux/cma.h | 2 +
include/linux/dma-contiguous.h | 6 ++
kernel/dma/Kconfig | 11 ++
kernel/dma/contiguous.c | 100 ++++++++++++++++--
mm/cma.h | 2 -
mm/hugetlb.c | 4 +-
8 files changed, 124 insertions(+), 14 deletions(-)
--
2.27.0
Right now, smmu is using dma_alloc_coherent() to get memory to save queues
and tables. Typically, on ARM64 server, there is a default CMA located at
node0, which could be far away from node2, node3 etc.
with this patch, smmu will get memory from local numa node to save command
queues and page tables. that means dma_unmap latency will be shrunk much.
Meanwhile, when iommu.passthrough is on, device drivers which call dma_
alloc_coherent() will also get local memory and avoid the travel between
numa nodes.
Acked-by: Will Deacon <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Marek Szyprowski <[email protected]>
Cc: Robin Murphy <[email protected]>
Cc: Ganapatrao Kulkarni <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Nicolas Saenz Julienne <[email protected]>
Cc: Steve Capper <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Mike Rapoport <[email protected]>
Signed-off-by: Barry Song <[email protected]>
---
-v7: add Will's acked-by
arch/arm64/mm/init.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 481d22c32a2e..f1c75957ff3c 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -429,6 +429,8 @@ void __init bootmem_init(void)
arm64_hugetlb_cma_reserve();
#endif
+ dma_pernuma_cma_reserve();
+
/*
* sparse_init() tries to allocate memory from memblock, so must be
* done after the fixed reservations
--
2.27.0
CMA_MAX_NAME should be visible to CMA's users as they might need it to set
the name of CMA areas and avoid hardcoding the size locally.
So this patch moves CMA_MAX_NAME from local header file to include/linux
header file and removes the magic number in hugetlb.c and contiguous.c.
Cc: Mike Kravetz <[email protected]>
Cc: Roman Gushchin <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Marek Szyprowski <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Robin Murphy <[email protected]>
Cc: Andrew Morton <[email protected]>
Signed-off-by: Barry Song <[email protected]>
---
this patch is fixing the magic number issue with respect to Will's comment here:
https://lore.kernel.org/linux-iommu/[email protected]/
include/linux/cma.h | 2 ++
kernel/dma/contiguous.c | 2 +-
mm/cma.h | 2 --
mm/hugetlb.c | 4 ++--
4 files changed, 5 insertions(+), 5 deletions(-)
diff --git a/include/linux/cma.h b/include/linux/cma.h
index 6ff79fefd01f..217999c8a762 100644
--- a/include/linux/cma.h
+++ b/include/linux/cma.h
@@ -18,6 +18,8 @@
#endif
+#define CMA_MAX_NAME 64
+
struct cma;
extern unsigned long totalcma_pages;
diff --git a/kernel/dma/contiguous.c b/kernel/dma/contiguous.c
index 0383c9b86715..d2d6b715c274 100644
--- a/kernel/dma/contiguous.c
+++ b/kernel/dma/contiguous.c
@@ -119,7 +119,7 @@ void __init dma_pernuma_cma_reserve(void)
for_each_online_node(nid) {
int ret;
- char name[20];
+ char name[CMA_MAX_NAME];
struct cma **cma = &dma_contiguous_pernuma_area[nid];
snprintf(name, sizeof(name), "pernuma%d", nid);
diff --git a/mm/cma.h b/mm/cma.h
index 20f6e24bc477..42ae082cb067 100644
--- a/mm/cma.h
+++ b/mm/cma.h
@@ -4,8 +4,6 @@
#include <linux/debugfs.h>
-#define CMA_MAX_NAME 64
-
struct cma {
unsigned long base_pfn;
unsigned long count;
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index a301c2d672bf..9eec0ea9ba68 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -5683,12 +5683,12 @@ void __init hugetlb_cma_reserve(int order)
reserved = 0;
for_each_node_state(nid, N_ONLINE) {
int res;
- char name[20];
+ char name[CMA_MAX_NAME];
size = min(per_node, hugetlb_cma_size - reserved);
size = round_up(size, PAGE_SIZE << order);
- snprintf(name, 20, "hugetlb%d", nid);
+ snprintf(name, sizeof(name), "hugetlb%d", nid);
res = cma_declare_contiguous_nid(0, size, 0, PAGE_SIZE << order,
0, false, name,
&hugetlb_cma[nid], nid);
--
2.27.0
Right now, drivers like ARM SMMU are using dma_alloc_coherent() to get
coherent DMA buffers to save their command queues and page tables. As
there is only one default CMA in the whole system, SMMUs on nodes other
than node0 will get remote memory. This leads to significant latency.
This patch provides per-numa CMA so that drivers like SMMU can get local
memory. Tests show localizing CMA can decrease dma_unmap latency much.
For instance, before this patch, SMMU on node2 has to wait for more than
560ns for the completion of CMD_SYNC in an empty command queue; with this
patch, it needs 240ns only.
A positive side effect of this patch would be improving performance even
further for those users who are worried about performance more than DMA
security and use iommu.passthrough=1 to skip IOMMU. With local CMA, all
drivers can get local coherent DMA buffers.
Cc: Jonathan Cameron <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Marek Szyprowski <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Robin Murphy <[email protected]>
Cc: Ganapatrao Kulkarni <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Nicolas Saenz Julienne <[email protected]>
Cc: Steve Capper <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Mike Rapoport <[email protected]>
Signed-off-by: Barry Song <[email protected]>
---
-v7: with respect to Will's comments
* move to use for_each_online_node
* add description if users don't specify pernuma_cma
* provide default value for CONFIG_DMA_PERNUMA_CMA
.../admin-guide/kernel-parameters.txt | 11 ++
include/linux/dma-contiguous.h | 6 ++
kernel/dma/Kconfig | 11 ++
kernel/dma/contiguous.c | 100 ++++++++++++++++--
4 files changed, 118 insertions(+), 10 deletions(-)
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index bdc1f33fd3d1..c609527fc35a 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -599,6 +599,17 @@
altogether. For more information, see
include/linux/dma-contiguous.h
+ pernuma_cma=nn[MG]
+ [ARM64,KNL]
+ Sets the size of kernel per-numa memory area for
+ contiguous memory allocations. A value of 0 disables
+ per-numa CMA altogether. And If this option is not
+ specificed, the default value is 0.
+ With per-numa CMA enabled, DMA users on node nid will
+ first try to allocate buffer from the pernuma area
+ which is located in node nid, if the allocation fails,
+ they will fallback to the global default memory area.
+
cmo_free_hint= [PPC] Format: { yes | no }
Specify whether pages are marked as being inactive
when they are freed. This is used in CMO environments
diff --git a/include/linux/dma-contiguous.h b/include/linux/dma-contiguous.h
index 03f8e98e3bcc..fe55e004f1f4 100644
--- a/include/linux/dma-contiguous.h
+++ b/include/linux/dma-contiguous.h
@@ -171,6 +171,12 @@ static inline void dma_free_contiguous(struct device *dev, struct page *page,
#endif
+#ifdef CONFIG_DMA_PERNUMA_CMA
+void dma_pernuma_cma_reserve(void);
+#else
+static inline void dma_pernuma_cma_reserve(void) { }
+#endif
+
#endif
#endif
diff --git a/kernel/dma/Kconfig b/kernel/dma/Kconfig
index 847a9d1fa634..c38979d45b13 100644
--- a/kernel/dma/Kconfig
+++ b/kernel/dma/Kconfig
@@ -118,6 +118,17 @@ config DMA_CMA
If unsure, say "n".
if DMA_CMA
+
+config DMA_PERNUMA_CMA
+ bool "Enable separate DMA Contiguous Memory Area for each NUMA Node"
+ default NUMA && ARM64
+ help
+ Enable this option to get pernuma CMA areas so that devices like
+ ARM64 SMMU can get local memory by DMA coherent APIs.
+
+ You can set the size of pernuma CMA by specifying "pernuma_cma=size"
+ on the kernel's command line.
+
comment "Default contiguous memory area size:"
config CMA_SIZE_MBYTES
diff --git a/kernel/dma/contiguous.c b/kernel/dma/contiguous.c
index cff7e60968b9..0383c9b86715 100644
--- a/kernel/dma/contiguous.c
+++ b/kernel/dma/contiguous.c
@@ -69,6 +69,19 @@ static int __init early_cma(char *p)
}
early_param("cma", early_cma);
+#ifdef CONFIG_DMA_PERNUMA_CMA
+
+static struct cma *dma_contiguous_pernuma_area[MAX_NUMNODES];
+static phys_addr_t pernuma_size_bytes __initdata;
+
+static int __init early_pernuma_cma(char *p)
+{
+ pernuma_size_bytes = memparse(p, &p);
+ return 0;
+}
+early_param("pernuma_cma", early_pernuma_cma);
+#endif
+
#ifdef CONFIG_CMA_SIZE_PERCENTAGE
static phys_addr_t __init __maybe_unused cma_early_percent_memory(void)
@@ -96,6 +109,34 @@ static inline __maybe_unused phys_addr_t cma_early_percent_memory(void)
#endif
+#ifdef CONFIG_DMA_PERNUMA_CMA
+void __init dma_pernuma_cma_reserve(void)
+{
+ int nid;
+
+ if (!pernuma_size_bytes)
+ return;
+
+ for_each_online_node(nid) {
+ int ret;
+ char name[20];
+ struct cma **cma = &dma_contiguous_pernuma_area[nid];
+
+ snprintf(name, sizeof(name), "pernuma%d", nid);
+ ret = cma_declare_contiguous_nid(0, pernuma_size_bytes, 0, 0,
+ 0, false, name, cma, nid);
+ if (ret) {
+ pr_warn("%s: reservation failed: err %d, node %d", __func__,
+ ret, nid);
+ continue;
+ }
+
+ pr_debug("%s: reserved %llu MiB on node %d\n", __func__,
+ (unsigned long long)pernuma_size_bytes / SZ_1M, nid);
+ }
+}
+#endif
+
/**
* dma_contiguous_reserve() - reserve area(s) for contiguous memory handling
* @limit: End address of the reserved memory (optional, 0 for any).
@@ -228,23 +269,44 @@ static struct page *cma_alloc_aligned(struct cma *cma, size_t size, gfp_t gfp)
* @size: Requested allocation size.
* @gfp: Allocation flags.
*
- * This function allocates contiguous memory buffer for specified device. It
- * tries to use device specific contiguous memory area if available, or the
- * default global one.
+ * tries to use device specific contiguous memory area if available, or it
+ * tries to use per-numa cma, if the allocation fails, it will fallback to
+ * try default global one.
*
- * Note that it byapss one-page size of allocations from the global area as
- * the addresses within one page are always contiguous, so there is no need
- * to waste CMA pages for that kind; it also helps reduce fragmentations.
+ * Note that it bypass one-page size of allocations from the per-numa and
+ * global area as the addresses within one page are always contiguous, so
+ * there is no need to waste CMA pages for that kind; it also helps reduce
+ * fragmentations.
*/
struct page *dma_alloc_contiguous(struct device *dev, size_t size, gfp_t gfp)
{
+#ifdef CONFIG_DMA_PERNUMA_CMA
+ int nid = dev_to_node(dev);
+#endif
+
/* CMA can be used only in the context which permits sleeping */
if (!gfpflags_allow_blocking(gfp))
return NULL;
if (dev->cma_area)
return cma_alloc_aligned(dev->cma_area, size, gfp);
- if (size <= PAGE_SIZE || !dma_contiguous_default_area)
+ if (size <= PAGE_SIZE)
+ return NULL;
+
+#ifdef CONFIG_DMA_PERNUMA_CMA
+ if (nid != NUMA_NO_NODE && !(gfp & (GFP_DMA | GFP_DMA32))) {
+ struct cma *cma = dma_contiguous_pernuma_area[nid];
+ struct page *page;
+
+ if (cma) {
+ page = cma_alloc_aligned(cma, size, gfp);
+ if (page)
+ return page;
+ }
+ }
+#endif
+ if (!dma_contiguous_default_area)
return NULL;
+
return cma_alloc_aligned(dma_contiguous_default_area, size, gfp);
}
@@ -261,9 +323,27 @@ 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)
{
- if (!cma_release(dev_get_cma_area(dev), page,
- PAGE_ALIGN(size) >> PAGE_SHIFT))
- __free_pages(page, get_order(size));
+ unsigned int count = PAGE_ALIGN(size) >> PAGE_SHIFT;
+
+ /* if dev has its own cma, free page from there */
+ if (dev->cma_area) {
+ if (cma_release(dev->cma_area, page, count))
+ return;
+ } else {
+ /*
+ * otherwise, page is from either per-numa cma or default cma
+ */
+#ifdef CONFIG_DMA_PERNUMA_CMA
+ if (cma_release(dma_contiguous_pernuma_area[page_to_nid(page)],
+ page, count))
+ return;
+#endif
+ if (cma_release(dma_contiguous_default_area, page, count))
+ return;
+ }
+
+ /* not in any cma, free from buddy */
+ __free_pages(page, get_order(size));
}
/*
--
2.27.0
On Fri, Aug 21, 2020 at 11:33:53PM +1200, Barry Song wrote:
> Right now, drivers like ARM SMMU are using dma_alloc_coherent() to get
> coherent DMA buffers to save their command queues and page tables. As
> there is only one default CMA in the whole system, SMMUs on nodes other
> than node0 will get remote memory. This leads to significant latency.
>
> This patch provides per-numa CMA so that drivers like SMMU can get local
> memory. Tests show localizing CMA can decrease dma_unmap latency much.
> For instance, before this patch, SMMU on node2 has to wait for more than
> 560ns for the completion of CMD_SYNC in an empty command queue; with this
> patch, it needs 240ns only.
>
> A positive side effect of this patch would be improving performance even
> further for those users who are worried about performance more than DMA
> security and use iommu.passthrough=1 to skip IOMMU. With local CMA, all
> drivers can get local coherent DMA buffers.
>
> Cc: Jonathan Cameron <[email protected]>
> Cc: Christoph Hellwig <[email protected]>
> Cc: Marek Szyprowski <[email protected]>
> Cc: Will Deacon <[email protected]>
> Cc: Robin Murphy <[email protected]>
> Cc: Ganapatrao Kulkarni <[email protected]>
> Cc: Catalin Marinas <[email protected]>
> Cc: Nicolas Saenz Julienne <[email protected]>
> Cc: Steve Capper <[email protected]>
> Cc: Andrew Morton <[email protected]>
> Cc: Mike Rapoport <[email protected]>
> Signed-off-by: Barry Song <[email protected]>
> ---
> -v7: with respect to Will's comments
> * move to use for_each_online_node
> * add description if users don't specify pernuma_cma
> * provide default value for CONFIG_DMA_PERNUMA_CMA
>
> .../admin-guide/kernel-parameters.txt | 11 ++
> include/linux/dma-contiguous.h | 6 ++
> kernel/dma/Kconfig | 11 ++
> kernel/dma/contiguous.c | 100 ++++++++++++++++--
> 4 files changed, 118 insertions(+), 10 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index bdc1f33fd3d1..c609527fc35a 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -599,6 +599,17 @@
> altogether. For more information, see
> include/linux/dma-contiguous.h
>
> + pernuma_cma=nn[MG]
Maybe cma_pernuma or cma_pernode?
> + [ARM64,KNL]
> + Sets the size of kernel per-numa memory area for
> + contiguous memory allocations. A value of 0 disables
> + per-numa CMA altogether. And If this option is not
> + specificed, the default value is 0.
> + With per-numa CMA enabled, DMA users on node nid will
> + first try to allocate buffer from the pernuma area
> + which is located in node nid, if the allocation fails,
> + they will fallback to the global default memory area.
> +
> cmo_free_hint= [PPC] Format: { yes | no }
> Specify whether pages are marked as being inactive
> when they are freed. This is used in CMO environments
> diff --git a/include/linux/dma-contiguous.h b/include/linux/dma-contiguous.h
> index 03f8e98e3bcc..fe55e004f1f4 100644
> --- a/include/linux/dma-contiguous.h
> +++ b/include/linux/dma-contiguous.h
> @@ -171,6 +171,12 @@ static inline void dma_free_contiguous(struct device *dev, struct page *page,
>
> #endif
>
> +#ifdef CONFIG_DMA_PERNUMA_CMA
> +void dma_pernuma_cma_reserve(void);
> +#else
> +static inline void dma_pernuma_cma_reserve(void) { }
> +#endif
> +
> #endif
>
> #endif
> diff --git a/kernel/dma/Kconfig b/kernel/dma/Kconfig
> index 847a9d1fa634..c38979d45b13 100644
> --- a/kernel/dma/Kconfig
> +++ b/kernel/dma/Kconfig
> @@ -118,6 +118,17 @@ config DMA_CMA
> If unsure, say "n".
>
> if DMA_CMA
> +
> +config DMA_PERNUMA_CMA
> + bool "Enable separate DMA Contiguous Memory Area for each NUMA Node"
> + default NUMA && ARM64
> + help
> + Enable this option to get pernuma CMA areas so that devices like
> + ARM64 SMMU can get local memory by DMA coherent APIs.
> +
> + You can set the size of pernuma CMA by specifying "pernuma_cma=size"
> + on the kernel's command line.
> +
> comment "Default contiguous memory area size:"
>
> config CMA_SIZE_MBYTES
> diff --git a/kernel/dma/contiguous.c b/kernel/dma/contiguous.c
> index cff7e60968b9..0383c9b86715 100644
> --- a/kernel/dma/contiguous.c
> +++ b/kernel/dma/contiguous.c
> @@ -69,6 +69,19 @@ static int __init early_cma(char *p)
> }
> early_param("cma", early_cma);
>
> +#ifdef CONFIG_DMA_PERNUMA_CMA
> +
> +static struct cma *dma_contiguous_pernuma_area[MAX_NUMNODES];
> +static phys_addr_t pernuma_size_bytes __initdata;
> +
> +static int __init early_pernuma_cma(char *p)
> +{
> + pernuma_size_bytes = memparse(p, &p);
> + return 0;
> +}
> +early_param("pernuma_cma", early_pernuma_cma);
> +#endif
> +
> #ifdef CONFIG_CMA_SIZE_PERCENTAGE
>
> static phys_addr_t __init __maybe_unused cma_early_percent_memory(void)
> @@ -96,6 +109,34 @@ static inline __maybe_unused phys_addr_t cma_early_percent_memory(void)
>
> #endif
>
> +#ifdef CONFIG_DMA_PERNUMA_CMA
> +void __init dma_pernuma_cma_reserve(void)
> +{
> + int nid;
> +
> + if (!pernuma_size_bytes)
> + return;
> +
> + for_each_online_node(nid) {
> + int ret;
> + char name[20];
> + struct cma **cma = &dma_contiguous_pernuma_area[nid];
> +
> + snprintf(name, sizeof(name), "pernuma%d", nid);
> + ret = cma_declare_contiguous_nid(0, pernuma_size_bytes, 0, 0,
> + 0, false, name, cma, nid);
> + if (ret) {
> + pr_warn("%s: reservation failed: err %d, node %d", __func__,
> + ret, nid);
> + continue;
> + }
> +
> + pr_debug("%s: reserved %llu MiB on node %d\n", __func__,
> + (unsigned long long)pernuma_size_bytes / SZ_1M, nid);
> + }
> +}
> +#endif
> +
> /**
> * dma_contiguous_reserve() - reserve area(s) for contiguous memory handling
> * @limit: End address of the reserved memory (optional, 0 for any).
> @@ -228,23 +269,44 @@ static struct page *cma_alloc_aligned(struct cma *cma, size_t size, gfp_t gfp)
> * @size: Requested allocation size.
> * @gfp: Allocation flags.
> *
> - * This function allocates contiguous memory buffer for specified device. It
> - * tries to use device specific contiguous memory area if available, or the
> - * default global one.
> + * tries to use device specific contiguous memory area if available, or it
> + * tries to use per-numa cma, if the allocation fails, it will fallback to
> + * try default global one.
> *
> - * Note that it byapss one-page size of allocations from the global area as
> - * the addresses within one page are always contiguous, so there is no need
> - * to waste CMA pages for that kind; it also helps reduce fragmentations.
> + * Note that it bypass one-page size of allocations from the per-numa and
> + * global area as the addresses within one page are always contiguous, so
> + * there is no need to waste CMA pages for that kind; it also helps reduce
> + * fragmentations.
> */
> struct page *dma_alloc_contiguous(struct device *dev, size_t size, gfp_t gfp)
> {
> +#ifdef CONFIG_DMA_PERNUMA_CMA
> + int nid = dev_to_node(dev);
> +#endif
> +
> /* CMA can be used only in the context which permits sleeping */
> if (!gfpflags_allow_blocking(gfp))
> return NULL;
> if (dev->cma_area)
> return cma_alloc_aligned(dev->cma_area, size, gfp);
> - if (size <= PAGE_SIZE || !dma_contiguous_default_area)
> + if (size <= PAGE_SIZE)
> + return NULL;
> +
> +#ifdef CONFIG_DMA_PERNUMA_CMA
> + if (nid != NUMA_NO_NODE && !(gfp & (GFP_DMA | GFP_DMA32))) {
> + struct cma *cma = dma_contiguous_pernuma_area[nid];
It could be that for some node reservation failedm than
dma_contiguous_pernuma_area[nid] would be NULL.
I'd add a fallback to another node here.
> + struct page *page;
> +
> + if (cma) {
> + page = cma_alloc_aligned(cma, size, gfp);
> + if (page)
> + return page;
> + }
> + }
> +#endif
I think the selection of the area can be put in a helper funciton and
then here we just try to allocate from the selected area. E.g.
static struct cma* dma_get_cma_area(struct device *dev)
{
#ifdef CONFIG_DMA_PERNUMA_CMA
int nid = dev_to_node(dev);
struct cma *cma = dma_contiguous_pernuma_area[nid];
if (!cma)
/* select cma from another node */ ;
return cma;
#else
return dma_contiguous_default_area;
#endif
}
struct page *dma_alloc_contiguous(struct device *dev, size_t size, gfp_t gfp)
{
struct cma *cma;
...
cma = dma_get_cma_area(dev);
if (!cma)
return NULL;
return cma_alloc_aligned(cma, size, gfp);
}
> + if (!dma_contiguous_default_area)
> return NULL;
> +
> return cma_alloc_aligned(dma_contiguous_default_area, size, gfp);
> }
>
> @@ -261,9 +323,27 @@ 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)
> {
> - if (!cma_release(dev_get_cma_area(dev), page,
> - PAGE_ALIGN(size) >> PAGE_SHIFT))
> - __free_pages(page, get_order(size));
Here as well, dev_get_cma_area() can be replaced with, say
dma_get_dev_cma_area(dev, page) that will hide the below logic.
> + unsigned int count = PAGE_ALIGN(size) >> PAGE_SHIFT;
> +
> + /* if dev has its own cma, free page from there */
> + if (dev->cma_area) {
> + if (cma_release(dev->cma_area, page, count))
> + return;
> + } else {
> + /*
> + * otherwise, page is from either per-numa cma or default cma
> + */
> +#ifdef CONFIG_DMA_PERNUMA_CMA
> + if (cma_release(dma_contiguous_pernuma_area[page_to_nid(page)],
> + page, count))
> + return;
> +#endif
> + if (cma_release(dma_contiguous_default_area, page, count))
> + return;
> + }
> +
> + /* not in any cma, free from buddy */
> + __free_pages(page, get_order(size));
> }
>
> /*
> --
> 2.27.0
>
>
--
Sincerely yours,
Mike.
On 8/21/20 4:33 AM, Barry Song wrote:
> ---
> -v7: with respect to Will's comments
> * move to use for_each_online_node
> * add description if users don't specify pernuma_cma
> * provide default value for CONFIG_DMA_PERNUMA_CMA
>
> .../admin-guide/kernel-parameters.txt | 11 ++
> include/linux/dma-contiguous.h | 6 ++
> kernel/dma/Kconfig | 11 ++
> kernel/dma/contiguous.c | 100 ++++++++++++++++--
> 4 files changed, 118 insertions(+), 10 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index bdc1f33fd3d1..c609527fc35a 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -599,6 +599,17 @@
> altogether. For more information, see
> include/linux/dma-contiguous.h
>
> + pernuma_cma=nn[MG]
> + [ARM64,KNL]
> + Sets the size of kernel per-numa memory area for
> + contiguous memory allocations. A value of 0 disables
> + per-numa CMA altogether. And If this option is not
> + specificed, the default value is 0.
> + With per-numa CMA enabled, DMA users on node nid will
> + first try to allocate buffer from the pernuma area
> + which is located in node nid, if the allocation fails,
> + they will fallback to the global default memory area.
> +
Entries in kernel-parameters.txt are supposed to be in alphabetical order
but this one is not. If you want to keep it near the cma= entry, you can
rename it like Mike suggested. Otherwise it needs to be moved.
> cmo_free_hint= [PPC] Format: { yes | no }
> Specify whether pages are marked as being inactive
> when they are freed. This is used in CMO environments
--
~Randy
Hi Barry,
Sorry for jumping in so late.
On 8/21/20 4:33 AM, Barry Song wrote:
>
> with per-numa CMA, smmu will get memory from local numa node to save command
> queues and page tables. that means dma_unmap latency will be shrunk much.
Since per-node CMA areas for hugetlb was introduced, I have been thinking
about the limited number of CMA areas. In most configurations, I believe
it is limited to 7. And, IIRC it is not something that can be changed at
runtime, you need to reconfig and rebuild to increase the number. In contrast
some configs have NODES_SHIFT set to 10. I wasn't too worried because of
the limited hugetlb use case. However, this series is adding another user
of per-node CMA areas.
With more users, should try to sync up number of CMA areas and number of
nodes? Or, perhaps I am worrying about nothing?
--
Mike Kravetz
> -----Original Message-----
> From: Mike Rapoport [mailto:[email protected]]
> Sent: Saturday, August 22, 2020 2:28 AM
> To: Song Bao Hua (Barry Song) <[email protected]>
> Cc: [email protected]; [email protected]; [email protected];
> [email protected]; [email protected];
> [email protected]; [email protected];
> [email protected]; [email protected];
> [email protected]; Zengtao (B) <[email protected]>;
> huangdaode <[email protected]>; Linuxarm <[email protected]>;
> Jonathan Cameron <[email protected]>; Nicolas Saenz Julienne
> <[email protected]>; Steve Capper <[email protected]>
> Subject: Re: [PATCH v7 1/3] dma-contiguous: provide the ability to reserve
> per-numa CMA
>
> On Fri, Aug 21, 2020 at 11:33:53PM +1200, Barry Song wrote:
> > Right now, drivers like ARM SMMU are using dma_alloc_coherent() to get
> > coherent DMA buffers to save their command queues and page tables. As
> > there is only one default CMA in the whole system, SMMUs on nodes other
> > than node0 will get remote memory. This leads to significant latency.
> >
> > This patch provides per-numa CMA so that drivers like SMMU can get local
> > memory. Tests show localizing CMA can decrease dma_unmap latency much.
> > For instance, before this patch, SMMU on node2 has to wait for more than
> > 560ns for the completion of CMD_SYNC in an empty command queue; with
> this
> > patch, it needs 240ns only.
> >
> > A positive side effect of this patch would be improving performance even
> > further for those users who are worried about performance more than DMA
> > security and use iommu.passthrough=1 to skip IOMMU. With local CMA, all
> > drivers can get local coherent DMA buffers.
> >
> > Cc: Jonathan Cameron <[email protected]>
> > Cc: Christoph Hellwig <[email protected]>
> > Cc: Marek Szyprowski <[email protected]>
> > Cc: Will Deacon <[email protected]>
> > Cc: Robin Murphy <[email protected]>
> > Cc: Ganapatrao Kulkarni <[email protected]>
> > Cc: Catalin Marinas <[email protected]>
> > Cc: Nicolas Saenz Julienne <[email protected]>
> > Cc: Steve Capper <[email protected]>
> > Cc: Andrew Morton <[email protected]>
> > Cc: Mike Rapoport <[email protected]>
> > Signed-off-by: Barry Song <[email protected]>
> > ---
> > -v7: with respect to Will's comments
> > * move to use for_each_online_node
> > * add description if users don't specify pernuma_cma
> > * provide default value for CONFIG_DMA_PERNUMA_CMA
> >
> > .../admin-guide/kernel-parameters.txt | 11 ++
> > include/linux/dma-contiguous.h | 6 ++
> > kernel/dma/Kconfig | 11 ++
> > kernel/dma/contiguous.c | 100
> ++++++++++++++++--
> > 4 files changed, 118 insertions(+), 10 deletions(-)
> >
> > diff --git a/Documentation/admin-guide/kernel-parameters.txt
> b/Documentation/admin-guide/kernel-parameters.txt
> > index bdc1f33fd3d1..c609527fc35a 100644
> > --- a/Documentation/admin-guide/kernel-parameters.txt
> > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > @@ -599,6 +599,17 @@
> > altogether. For more information, see
> > include/linux/dma-contiguous.h
> >
> > + pernuma_cma=nn[MG]
>
> Maybe cma_pernuma or cma_pernode?
Sounds good.
>
> > + [ARM64,KNL]
> > + Sets the size of kernel per-numa memory area for
> > + contiguous memory allocations. A value of 0 disables
> > + per-numa CMA altogether. And If this option is not
> > + specificed, the default value is 0.
> > + With per-numa CMA enabled, DMA users on node nid will
> > + first try to allocate buffer from the pernuma area
> > + which is located in node nid, if the allocation fails,
> > + they will fallback to the global default memory area.
> > +
> > cmo_free_hint= [PPC] Format: { yes | no }
> > Specify whether pages are marked as being inactive
> > when they are freed. This is used in CMO environments
> > diff --git a/include/linux/dma-contiguous.h
> b/include/linux/dma-contiguous.h
> > index 03f8e98e3bcc..fe55e004f1f4 100644
> > --- a/include/linux/dma-contiguous.h
> > +++ b/include/linux/dma-contiguous.h
> > @@ -171,6 +171,12 @@ static inline void dma_free_contiguous(struct
> device *dev, struct page *page,
> >
> > #endif
> >
> > +#ifdef CONFIG_DMA_PERNUMA_CMA
> > +void dma_pernuma_cma_reserve(void);
> > +#else
> > +static inline void dma_pernuma_cma_reserve(void) { }
> > +#endif
> > +
> > #endif
> >
> > #endif
> > diff --git a/kernel/dma/Kconfig b/kernel/dma/Kconfig
> > index 847a9d1fa634..c38979d45b13 100644
> > --- a/kernel/dma/Kconfig
> > +++ b/kernel/dma/Kconfig
> > @@ -118,6 +118,17 @@ config DMA_CMA
> > If unsure, say "n".
> >
> > if DMA_CMA
> > +
> > +config DMA_PERNUMA_CMA
> > + bool "Enable separate DMA Contiguous Memory Area for each NUMA
> Node"
> > + default NUMA && ARM64
> > + help
> > + Enable this option to get pernuma CMA areas so that devices like
> > + ARM64 SMMU can get local memory by DMA coherent APIs.
> > +
> > + You can set the size of pernuma CMA by specifying
> "pernuma_cma=size"
> > + on the kernel's command line.
> > +
> > comment "Default contiguous memory area size:"
> >
> > config CMA_SIZE_MBYTES
> > diff --git a/kernel/dma/contiguous.c b/kernel/dma/contiguous.c
> > index cff7e60968b9..0383c9b86715 100644
> > --- a/kernel/dma/contiguous.c
> > +++ b/kernel/dma/contiguous.c
> > @@ -69,6 +69,19 @@ static int __init early_cma(char *p)
> > }
> > early_param("cma", early_cma);
> >
> > +#ifdef CONFIG_DMA_PERNUMA_CMA
> > +
> > +static struct cma *dma_contiguous_pernuma_area[MAX_NUMNODES];
> > +static phys_addr_t pernuma_size_bytes __initdata;
> > +
> > +static int __init early_pernuma_cma(char *p)
> > +{
> > + pernuma_size_bytes = memparse(p, &p);
> > + return 0;
> > +}
> > +early_param("pernuma_cma", early_pernuma_cma);
> > +#endif
> > +
> > #ifdef CONFIG_CMA_SIZE_PERCENTAGE
> >
> > static phys_addr_t __init __maybe_unused
> cma_early_percent_memory(void)
> > @@ -96,6 +109,34 @@ static inline __maybe_unused phys_addr_t
> cma_early_percent_memory(void)
> >
> > #endif
> >
> > +#ifdef CONFIG_DMA_PERNUMA_CMA
> > +void __init dma_pernuma_cma_reserve(void)
> > +{
> > + int nid;
> > +
> > + if (!pernuma_size_bytes)
> > + return;
> > +
> > + for_each_online_node(nid) {
> > + int ret;
> > + char name[20];
> > + struct cma **cma = &dma_contiguous_pernuma_area[nid];
> > +
> > + snprintf(name, sizeof(name), "pernuma%d", nid);
> > + ret = cma_declare_contiguous_nid(0, pernuma_size_bytes, 0, 0,
> > + 0, false, name, cma, nid);
> > + if (ret) {
> > + pr_warn("%s: reservation failed: err %d, node %d", __func__,
> > + ret, nid);
> > + continue;
> > + }
> > +
> > + pr_debug("%s: reserved %llu MiB on node %d\n", __func__,
> > + (unsigned long long)pernuma_size_bytes / SZ_1M, nid);
> > + }
> > +}
> > +#endif
> > +
> > /**
> > * dma_contiguous_reserve() - reserve area(s) for contiguous memory
> handling
> > * @limit: End address of the reserved memory (optional, 0 for any).
> > @@ -228,23 +269,44 @@ static struct page *cma_alloc_aligned(struct cma
> *cma, size_t size, gfp_t gfp)
> > * @size: Requested allocation size.
> > * @gfp: Allocation flags.
> > *
> > - * This function allocates contiguous memory buffer for specified device. It
> > - * tries to use device specific contiguous memory area if available, or the
> > - * default global one.
> > + * tries to use device specific contiguous memory area if available, or it
> > + * tries to use per-numa cma, if the allocation fails, it will fallback to
> > + * try default global one.
> > *
> > - * Note that it byapss one-page size of allocations from the global area as
> > - * the addresses within one page are always contiguous, so there is no need
> > - * to waste CMA pages for that kind; it also helps reduce fragmentations.
> > + * Note that it bypass one-page size of allocations from the per-numa and
> > + * global area as the addresses within one page are always contiguous, so
> > + * there is no need to waste CMA pages for that kind; it also helps reduce
> > + * fragmentations.
> > */
> > struct page *dma_alloc_contiguous(struct device *dev, size_t size, gfp_t
> gfp)
> > {
> > +#ifdef CONFIG_DMA_PERNUMA_CMA
> > + int nid = dev_to_node(dev);
> > +#endif
> > +
> > /* CMA can be used only in the context which permits sleeping */
> > if (!gfpflags_allow_blocking(gfp))
> > return NULL;
> > if (dev->cma_area)
> > return cma_alloc_aligned(dev->cma_area, size, gfp);
> > - if (size <= PAGE_SIZE || !dma_contiguous_default_area)
> > + if (size <= PAGE_SIZE)
> > + return NULL;
> > +
> > +#ifdef CONFIG_DMA_PERNUMA_CMA
> > + if (nid != NUMA_NO_NODE && !(gfp & (GFP_DMA | GFP_DMA32))) {
> > + struct cma *cma = dma_contiguous_pernuma_area[nid];
>
> It could be that for some node reservation failedm than
> dma_contiguous_pernuma_area[nid] would be NULL.
> I'd add a fallback to another node here.
This has been done.
If dma_contiguous_pernuma_area[nid] is null, it will fallback to the default global cma.
>
> > + struct page *page;
> > +
> > + if (cma) {
> > + page = cma_alloc_aligned(cma, size, gfp);
> > + if (page)
> > + return page;
> > + }
> > + }
> > +#endif
>
> I think the selection of the area can be put in a helper funciton and
> then here we just try to allocate from the selected area. E.g.
>
> static struct cma* dma_get_cma_area(struct device *dev)
> {
> #ifdef CONFIG_DMA_PERNUMA_CMA
> int nid = dev_to_node(dev);
> struct cma *cma = dma_contiguous_pernuma_area[nid];
>
> if (!cma)
> /* select cma from another node */ ;
>
> return cma;
> #else
> return dma_contiguous_default_area;
> #endif
> }
>
It is possible dma_contiguous_pernuma_area[nid] is not null, but we fail to get memory
from it due to it is either full or has no GFP_DMA(32) support. In this case, we still need
to fallback to the default global cma. So the code is trying pernuma_cma, then trying
default global cma. It is not picking one from the two areas. It is trying both.
> struct page *dma_alloc_contiguous(struct device *dev, size_t size, gfp_t gfp)
> {
> struct cma *cma;
> ...
>
>
> cma = dma_get_cma_area(dev);
> if (!cma)
> return NULL;
>
> return cma_alloc_aligned(cma, size, gfp);
> }
>
> > + if (!dma_contiguous_default_area)
> > return NULL;
> > +
> > return cma_alloc_aligned(dma_contiguous_default_area, size, gfp);
> > }
> >
> > @@ -261,9 +323,27 @@ 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)
> > {
> > - if (!cma_release(dev_get_cma_area(dev), page,
> > - PAGE_ALIGN(size) >> PAGE_SHIFT))
> > - __free_pages(page, get_order(size));
>
> Here as well, dev_get_cma_area() can be replaced with, say
> dma_get_dev_cma_area(dev, page) that will hide the below logic.
As explained above, this won't work.
>
> > + unsigned int count = PAGE_ALIGN(size) >> PAGE_SHIFT;
> > +
> > + /* if dev has its own cma, free page from there */
> > + if (dev->cma_area) {
> > + if (cma_release(dev->cma_area, page, count))
> > + return;
> > + } else {
> > + /*
> > + * otherwise, page is from either per-numa cma or default cma
> > + */
> > +#ifdef CONFIG_DMA_PERNUMA_CMA
> > + if (cma_release(dma_contiguous_pernuma_area[page_to_nid(page)],
> > + page, count))
> > + return;
> > +#endif
> > + if (cma_release(dma_contiguous_default_area, page, count))
> > + return;
> > + }
> > +
> > + /* not in any cma, free from buddy */
> > + __free_pages(page, get_order(size));
> > }
> >
> > /*
> > --
> > 2.27.0
> >
> >
Thanks
Barry
> -----Original Message-----
> From: Randy Dunlap [mailto:[email protected]]
> Sent: Saturday, August 22, 2020 4:08 AM
> To: Song Bao Hua (Barry Song) <[email protected]>; [email protected];
> [email protected]; [email protected]; [email protected];
> [email protected]; [email protected];
> [email protected]
> Cc: [email protected]; [email protected];
> [email protected]; Zengtao (B) <[email protected]>;
> huangdaode <[email protected]>; Linuxarm <[email protected]>;
> Jonathan Cameron <[email protected]>; Nicolas Saenz Julienne
> <[email protected]>; Steve Capper <[email protected]>; Mike
> Rapoport <[email protected]>
> Subject: Re: [PATCH v7 1/3] dma-contiguous: provide the ability to reserve
> per-numa CMA
>
> On 8/21/20 4:33 AM, Barry Song wrote:
> > ---
> > -v7: with respect to Will's comments
> > * move to use for_each_online_node
> > * add description if users don't specify pernuma_cma
> > * provide default value for CONFIG_DMA_PERNUMA_CMA
> >
> > .../admin-guide/kernel-parameters.txt | 11 ++
> > include/linux/dma-contiguous.h | 6 ++
> > kernel/dma/Kconfig | 11 ++
> > kernel/dma/contiguous.c | 100
> ++++++++++++++++--
> > 4 files changed, 118 insertions(+), 10 deletions(-)
> >
> > diff --git a/Documentation/admin-guide/kernel-parameters.txt
> b/Documentation/admin-guide/kernel-parameters.txt
> > index bdc1f33fd3d1..c609527fc35a 100644
> > --- a/Documentation/admin-guide/kernel-parameters.txt
> > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > @@ -599,6 +599,17 @@
> > altogether. For more information, see
> > include/linux/dma-contiguous.h
> >
> > + pernuma_cma=nn[MG]
> > + [ARM64,KNL]
> > + Sets the size of kernel per-numa memory area for
> > + contiguous memory allocations. A value of 0 disables
> > + per-numa CMA altogether. And If this option is not
> > + specificed, the default value is 0.
> > + With per-numa CMA enabled, DMA users on node nid will
> > + first try to allocate buffer from the pernuma area
> > + which is located in node nid, if the allocation fails,
> > + they will fallback to the global default memory area.
> > +
>
> Entries in kernel-parameters.txt are supposed to be in alphabetical order
> but this one is not. If you want to keep it near the cma= entry, you can
> rename it like Mike suggested. Otherwise it needs to be moved.
As I've replied in Mike's comment, I'd like to rename it to cma_per...
>
>
> > cmo_free_hint= [PPC] Format: { yes | no }
> > Specify whether pages are marked as being inactive
> > when they are freed. This is used in CMO environments
>
>
>
> --
> ~Randy
Thanks
Barry
> -----Original Message-----
> From: Mike Kravetz [mailto:[email protected]]
> Sent: Saturday, August 22, 2020 5:53 AM
> To: Song Bao Hua (Barry Song) <[email protected]>; [email protected];
> [email protected]; [email protected]; [email protected];
> [email protected]; [email protected];
> [email protected]
> Cc: [email protected]; [email protected];
> [email protected]; Zengtao (B) <[email protected]>;
> huangdaode <[email protected]>; Linuxarm <[email protected]>
> Subject: Re: [PATCH v7 0/3] make dma_alloc_coherent NUMA-aware by
> per-NUMA CMA
>
> Hi Barry,
> Sorry for jumping in so late.
>
> On 8/21/20 4:33 AM, Barry Song wrote:
> >
> > with per-numa CMA, smmu will get memory from local numa node to save
> command
> > queues and page tables. that means dma_unmap latency will be shrunk
> much.
>
> Since per-node CMA areas for hugetlb was introduced, I have been thinking
> about the limited number of CMA areas. In most configurations, I believe
> it is limited to 7. And, IIRC it is not something that can be changed at
> runtime, you need to reconfig and rebuild to increase the number. In contrast
> some configs have NODES_SHIFT set to 10. I wasn't too worried because of
> the limited hugetlb use case. However, this series is adding another user
> of per-node CMA areas.
>
> With more users, should try to sync up number of CMA areas and number of
> nodes? Or, perhaps I am worrying about nothing?
Hi Mike,
The current limitation is 8. If the server has 4 nodes and we enable both pernuma
CMA and hugetlb, the last node will fail to get one cma area as the default
global cma area will take 1 of 8. So users need to change menuconfig.
If the server has 8 nodes, we enable one of pernuma cma and hugetlb, one node
will fail to get cma.
We may set the default number of CMA areas as 8+MAX_NODES(if hugetlb enabled) +
MAX_NODES(if pernuma cma enabled) if we don't expect users to change config, but
right now hugetlb has not an option in Kconfig to enable or disable like pernuma cma
has DMA_PERNUMA_CMA.
> --
> Mike Kravetz
Thanks
Barry