[PATCH v4 0/3] dma-mapping, powerpc, nvme: introduce the DMA_ATTR_NO_WARN attribute

[PATCH v4 0/3] dma-mapping, powerpc, nvme: introduce the DMA_ATTR_NO_WARN attribute

[Mauricio Faria de Oliveira]

This patchset introduces dma_attr DMA_ATTR_NO_WARN (just like __GFP_NOWARN),
which tells the DMA-mapping subsystem to suppress allocation failure reports.

On some architectures allocation failures are reported with error messages
to the system logs.  Although this can help to identify and debug problems,
drivers which handle failures (eg, retry later) have no problems with them,
and can actually flood the system logs with error messages that aren't any
problem at all, depending on the implementation of the retry mechanism.

So, this provides a way for drivers to avoid those error messages on calls
where allocation failures are not a problem, and shouldn't bother the logs.

 - Patch 1/3 introduces the dma_attr DMA_ATTR_NO_WARN.

 - Patch 2/3 implements support for it on powerpc arch (where this problem
             was observed;  it's possible to extend support for more archs)

 - Patch 3/3 implements it on the nvme driver (which might repeatedly trip
             on allocation failures due to high load, flooding system logs
             with error messages at least on powerpc: "iommu_alloc failed")

Changelog:
 v4:
  - rebase for commit 53a4b60 dma-mapping: use unsigned long for dma_attrs.
  - reorder patches 2/3 and 3/3.
 v3:
  - nvme: use DMA_ATTR_NO_WARN when ret = BLK_MQ_RQ_QUEUE_BUSY (io will be
    requeued) but not when ret = BLK_MQ_RQ_QUEUE_ERROR (io will be failed).
    thanks: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>
 v2:
  - all: address warnings from checkpatch.pl (line wrapping and typos)

Tested on next-20160801.

Mauricio Faria de Oliveira (3):
  dma-mapping: introduce the DMA_ATTR_NO_WARN attribute
  powerpc: implement the DMA_ATTR_NO_WARN attribute
  nvme: use the DMA_ATTR_NO_WARN attribute

 Documentation/DMA-attributes.txt | 17 +++++++++++++++++
 arch/powerpc/kernel/iommu.c      |  6 ++++--
 drivers/nvme/host/pci.c          |  3 ++-
 include/linux/dma-mapping.h      |  5 +++++
 4 files changed, 28 insertions(+), 3 deletions(-)

-- 
1.8.3.1

[PATCH 1/3] dma-mapping: introduce the DMA_ATTR_NO_WARN attribute

[Mauricio Faria de Oliveira]

Introduce the DMA_ATTR_NO_WARN attribute, and document it.

Signed-off-by: Mauricio Faria de Oliveira <mauricfo@linux.vnet.ibm.com>
---
 Documentation/DMA-attributes.txt | 17 +++++++++++++++++
 include/linux/dma-mapping.h      |  5 +++++
 2 files changed, 22 insertions(+)

diff --git a/Documentation/DMA-attributes.txt b/Documentation/DMA-attributes.txt
index 2d455a5..98bf7ac 100644
--- a/Documentation/DMA-attributes.txt
+++ b/Documentation/DMA-attributes.txt
@@ -126,3 +126,20 @@ means that we won't try quite as hard to get them.
 
 NOTE: At the moment DMA_ATTR_ALLOC_SINGLE_PAGES is only implemented on ARM,
 though ARM64 patches will likely be posted soon.
+
+DMA_ATTR_NO_WARN
+----------------
+
+This tells the DMA-mapping subsystem to suppress allocation failure reports
+(similarly to __GFP_NOWARN).
+
+On some architectures allocation failures are reported with error messages
+to the system logs.  Although this can help to identify and debug problems,
+drivers which handle failures (eg, retry later) have no problems with them,
+and can actually flood the system logs with error messages that aren't any
+problem at all, depending on the implementation of the retry mechanism.
+
+So, this provides a way for drivers to avoid those error messages on calls
+where allocation failures are not a problem, and shouldn't bother the logs.
+
+NOTE: At the moment DMA_ATTR_NO_WARN is only implemented on PowerPC.
diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index 66533e1..6efbd27 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -56,6 +56,11 @@
  * that gives better TLB efficiency.
  */
 #define DMA_ATTR_ALLOC_SINGLE_PAGES	(1UL << 7)
+/*
+ * DMA_ATTR_NO_WARN: This tells the DMA-mapping subsystem to suppress
+ * allocation failure reports (similarly to __GFP_NOWARN).
+ */
+#define DMA_ATTR_NO_WARN	(1UL << 8)
 
 /*
  * A dma_addr_t can hold any valid DMA or bus address for the platform.
-- 
1.8.3.1

[PATCH 2/3] powerpc: implement the DMA_ATTR_NO_WARN attribute

[Mauricio Faria de Oliveira]

Add support for the DMA_ATTR_NO_WARN attribute on powerpc iommu code.

Signed-off-by: Mauricio Faria de Oliveira <mauricfo@linux.vnet.ibm.com>
---
 arch/powerpc/kernel/iommu.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/kernel/iommu.c b/arch/powerpc/kernel/iommu.c
index 37d6e74..5f202a5 100644
--- a/arch/powerpc/kernel/iommu.c
+++ b/arch/powerpc/kernel/iommu.c
@@ -479,7 +479,8 @@ int ppc_iommu_map_sg(struct device *dev, struct iommu_table *tbl,
 
 		/* Handle failure */
 		if (unlikely(entry == DMA_ERROR_CODE)) {
-			if (printk_ratelimit())
+			if (!(attrs & DMA_ATTR_NO_WARN) &&
+			    printk_ratelimit())
 				dev_info(dev, "iommu_alloc failed, tbl %p "
 					 "vaddr %lx npages %lu\n", tbl, vaddr,
 					 npages);
@@ -776,7 +777,8 @@ dma_addr_t iommu_map_page(struct device *dev, struct iommu_table *tbl,
 					 mask >> tbl->it_page_shift, align,
 					 attrs);
 		if (dma_handle == DMA_ERROR_CODE) {
-			if (printk_ratelimit())  {
+			if (!(attrs & DMA_ATTR_NO_WARN) &&
+			    printk_ratelimit())  {
 				dev_info(dev, "iommu_alloc failed, tbl %p "
 					 "vaddr %p npages %d\n", tbl, vaddr,
 					 npages);
-- 
1.8.3.1

[PATCH 3/3] nvme: use the DMA_ATTR_NO_WARN attribute

[Mauricio Faria de Oliveira]

Use the DMA_ATTR_NO_WARN attribute for the dma_map_sg() call of the nvme
driver that returns BLK_MQ_RQ_QUEUE_BUSY (not for BLK_MQ_RQ_QUEUE_ERROR).

Signed-off-by: Mauricio Faria de Oliveira <mauricfo@linux.vnet.ibm.com>
Reviewed-by: Gabriel Krisman Bertazi <krisman@linux.vnet.ibm.com>
---
 drivers/nvme/host/pci.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index d7c33f9..eeaeae0 100644
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -503,7 +503,8 @@ static int nvme_map_data(struct nvme_dev *dev, struct request *req,
 		goto out;
 
 	ret = BLK_MQ_RQ_QUEUE_BUSY;
-	if (!dma_map_sg(dev->dev, iod->sg, iod->nents, dma_dir))
+	if (!dma_map_sg_attrs(dev->dev, iod->sg, iod->nents, dma_dir,
+				DMA_ATTR_NO_WARN))
 		goto out;
 
 	if (!nvme_setup_prps(dev, req, size))
-- 
1.8.3.1