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Subject[PATCH v2] libnvdimm, region_devs: stop NDD_ALIASING bit test if one test pass
Date
From: Ocean He <hehy1@lenovo.com>

There is no need to finish entire loop to execute NDD_ALIASING bit test
against every nvdimm->flags. In practice, all the nd_mapping->nvdimm
have the same flags. So it's safe to return ND_DEVICE_NAMESPACE_PMEM
if the NDD_ALIASING bit is found inside the loop, while saving a few
cpu cycles.

Signed-off-by: Ocean He <hehy1@lenovo.com>
---
v1: https://lkml.org/lkml/2018/8/19/4
v2: Per Vishal's comments in patch v1, remove 'alias' variable.
In the loop, just return ND_DEVICE_NAMESPACE_PMEM if the NDD_ALIASING bit is
found for any mapping.
Outside the loop, simply return ND_DEVICE_NAMESPACE_IO.

The following test pass on Lenovo ThinkSystem SR630 based on 4.19-rc1.
# ndctl create-namespace -r region0 -s 1g -t pmem -m fsdax
# ndctl create-namespace -r region0 -s 1g -t pmem -m sector
# ndctl create-namespace -r region0 -s 1g -t pmem -m devdax
# ndctl list
[
{
"dev":"namespace0.2",
"mode":"devdax",
"map":"dev",
"size":1054867456,
"uuid":"fc3a2126-9b8e-4ab4-baa4-a3ec7f62a326",
"raw_uuid":"eadc6965-daee-48c5-a0ae-1865ee0c8573",
"chardev":"dax0.2",
"numa_node":0
},
{
"dev":"namespace0.1",
"mode":"sector",
"size":1071616000,
"uuid":"0d81d040-93a1-45c6-9791-3dbb7b5f89d2",
"raw_uuid":"2b1b29e6-0510-4dcf-9902-43b77ccb9df5",
"sector_size":4096,
"blockdev":"pmem0.1s",
"numa_node":0
},
{
"dev":"namespace0.0",
"mode":"fsdax",
"map":"dev",
"size":1054867456,
"uuid":"cbff92ed-cd45-4d24-9353-7a56d42122b1",
"raw_uuid":"f6ea1001-5ef0-4942-889a-99005079ab5d",
"sector_size":512,
"blockdev":"pmem0",
"numa_node":0
}
]

# reboot and OS could boot up normally
# ndctl destroy-namespace namespace0.2 -f
# ndctl destroy-namespace namespace0.1 -f
# ndctl destroy-namespace namespace0.0 -f

drivers/nvdimm/region_devs.c | 13 ++++++-------
1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/drivers/nvdimm/region_devs.c b/drivers/nvdimm/region_devs.c
index fa37afc..16ee153 100644
--- a/drivers/nvdimm/region_devs.c
+++ b/drivers/nvdimm/region_devs.c
@@ -228,19 +228,18 @@ void nd_blk_region_set_provider_data(struct nd_blk_region *ndbr, void *data)
int nd_region_to_nstype(struct nd_region *nd_region)
{
if (is_memory(&nd_region->dev)) {
- u16 i, alias;
+ u16 i;

- for (i = 0, alias = 0; i < nd_region->ndr_mappings; i++) {
+ for (i = 0; i < nd_region->ndr_mappings; i++) {
struct nd_mapping *nd_mapping = &nd_region->mapping[i];
struct nvdimm *nvdimm = nd_mapping->nvdimm;

if (test_bit(NDD_ALIASING, &nvdimm->flags))
- alias++;
+ return ND_DEVICE_NAMESPACE_PMEM;
}
- if (alias)
- return ND_DEVICE_NAMESPACE_PMEM;
- else
- return ND_DEVICE_NAMESPACE_IO;
+
+ return ND_DEVICE_NAMESPACE_IO;
+
} else if (is_nd_blk(&nd_region->dev)) {
return ND_DEVICE_NAMESPACE_BLK;
}
--
1.8.3.1
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