[PATCH 2/2] libnvdimm: don't flush power-fail protected CPU caches

From: Ross Zwisler
Date: Tue Jun 05 2018 - 16:59:09 EST


This commit:

5fdf8e5ba566 ("libnvdimm: re-enable deep flush for pmem devices via fsync()")

intended to make sure that deep flush was always available even on
platforms which support a power-fail protected CPU cache. An unintended
side effect of this change was that we also lost the ability to skip
flushing CPU caches on those power-fail protected CPU cache.

Signed-off-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Fixes: 5fdf8e5ba566 ("libnvdimm: re-enable deep flush for pmem devices via fsync()")
---
drivers/dax/super.c | 20 +++++++++++++++++++-
drivers/nvdimm/pmem.c | 2 ++
include/linux/dax.h | 9 +++++++++
3 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/drivers/dax/super.c b/drivers/dax/super.c
index c2c46f96b18c..457e0bb6c936 100644
--- a/drivers/dax/super.c
+++ b/drivers/dax/super.c
@@ -152,6 +152,8 @@ enum dax_device_flags {
DAXDEV_ALIVE,
/* gate whether dax_flush() calls the low level flush routine */
DAXDEV_WRITE_CACHE,
+ /* only flush the CPU caches if they are not power fail protected */
+ DAXDEV_FLUSH_ON_SYNC,
};

/**
@@ -283,7 +285,8 @@ EXPORT_SYMBOL_GPL(dax_copy_from_iter);
void arch_wb_cache_pmem(void *addr, size_t size);
void dax_flush(struct dax_device *dax_dev, void *addr, size_t size)
{
- if (unlikely(!dax_write_cache_enabled(dax_dev)))
+ if (unlikely(!dax_write_cache_enabled(dax_dev)) ||
+ !dax_flush_on_sync_enabled(dax_dev))
return;

arch_wb_cache_pmem(addr, size);
@@ -310,6 +313,21 @@ bool dax_write_cache_enabled(struct dax_device *dax_dev)
}
EXPORT_SYMBOL_GPL(dax_write_cache_enabled);

+void dax_flush_on_sync(struct dax_device *dax_dev, bool flush)
+{
+ if (flush)
+ set_bit(DAXDEV_FLUSH_ON_SYNC, &dax_dev->flags);
+ else
+ clear_bit(DAXDEV_FLUSH_ON_SYNC, &dax_dev->flags);
+}
+EXPORT_SYMBOL_GPL(dax_flush_on_sync);
+
+bool dax_flush_on_sync_enabled(struct dax_device *dax_dev)
+{
+ return test_bit(DAXDEV_FLUSH_ON_SYNC, &dax_dev->flags);
+}
+EXPORT_SYMBOL_GPL(dax_flush_on_sync_enabled);
+
bool dax_alive(struct dax_device *dax_dev)
{
lockdep_assert_held(&dax_srcu);
diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
index 9d714926ecf5..faeb2deae7f0 100644
--- a/drivers/nvdimm/pmem.c
+++ b/drivers/nvdimm/pmem.c
@@ -414,6 +414,8 @@ static int pmem_attach_disk(struct device *dev,
return -ENOMEM;
}
dax_write_cache(dax_dev, wbc);
+ dax_flush_on_sync(dax_dev,
+ !test_bit(ND_REGION_PERSIST_CACHE, &nd_region->flags));
pmem->dax_dev = dax_dev;

gendev = disk_to_dev(disk);
diff --git a/include/linux/dax.h b/include/linux/dax.h
index f9eb22ad341e..1e6086405a1a 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -32,6 +32,8 @@ void put_dax(struct dax_device *dax_dev);
void kill_dax(struct dax_device *dax_dev);
void dax_write_cache(struct dax_device *dax_dev, bool wc);
bool dax_write_cache_enabled(struct dax_device *dax_dev);
+void dax_flush_on_sync(struct dax_device *dax_dev, bool flush);
+bool dax_flush_on_sync_enabled(struct dax_device *dax_dev);
#else
static inline struct dax_device *dax_get_by_host(const char *host)
{
@@ -59,6 +61,13 @@ static inline bool dax_write_cache_enabled(struct dax_device *dax_dev)
{
return false;
}
+static inline void dax_flush_on_sync(struct dax_device *dax_dev, bool flush)
+{
+}
+static inline bool dax_flush_on_sync_enabled(struct dax_device *dax_dev)
+{
+ return false;
+}
#endif

struct writeback_control;
--
2.14.4