Thread (14 messages) 14 messages, 4 authors, 2020-08-31

Re: [PATCH v6 1/2] dma-contiguous: provide the ability to reserve per-numa CMA

From: Will Deacon <will@kernel.org>
Date: 2020-08-21 08:47:32
Also in: linux-iommu, lkml

On Fri, Aug 21, 2020 at 02:26:14PM +1200, Barry Song wrote:
quoted hunk ↗ jump to hunk
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index bdc1f33fd3d1..3f33b89aeab5 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -599,6 +599,15 @@
 			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. 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.
What is the default behaviour if this option is not specified? Seems like
that should be mentioned here.
quoted hunk ↗ jump to hunk
diff --git a/kernel/dma/Kconfig b/kernel/dma/Kconfig
index 847a9d1fa634..db7a37ed35eb 100644
--- a/kernel/dma/Kconfig
+++ b/kernel/dma/Kconfig
@@ -118,6 +118,16 @@ 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"
I don't understand the need for this config option. If you have DMA_DMA and
you have NUMA, why wouldn't you want this enabled?
quoted hunk ↗ jump to hunk
+	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..89b95f10e56d 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;
If this is useful (I assume it is), then I think we should have a non-zero
default value, a bit like normal CMA does via CMA_SIZE_MBYTES.
+	for_each_node_state(nid, N_ONLINE) {
for_each_online_node() {
+		int ret;
+		char name[20];
20?

Ah, wait, this is copy-pasta from hugetlb_cma_reserve(). Can you factor out
the common parts at all?

Will

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