Do not ask for dax_direct_access() to retrieve a pfn in the
DAX_DRIVER_DEBUG=n case. This avoids an early call to memmap_sync() in
the driver.
Now that QUEUE_FLAG_DAX usage has been fixed the validation of the pfn
is only useful for dax driver developers. It is safe to assume that
pmem, dcssblk, and device-mapper-dax are correct with respect to dax
operation, so only retrieve the pfn for debug builds when qualifying a
new dax driver, if one ever arrives.
The moves the first consumption of a pfn from ->direct_access() to the
first dax mapping fault, rather than initial filesystem mount. I.e. more
time for memmap init to run in the background.
Cc: Jan Kara <jack@xxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
---
drivers/dax/Kconfig | 10 ++++++++
drivers/dax/super.c | 64 ++++++++++++++++++++++++++++++++-------------------
2 files changed, 50 insertions(+), 24 deletions(-)
diff --git a/drivers/dax/Kconfig b/drivers/dax/Kconfig
index e0700bf4893a..b32f8827b983 100644
--- a/drivers/dax/Kconfig
+++ b/drivers/dax/Kconfig
@@ -9,6 +9,16 @@ menuconfig DAX
if DAX
+config DAX_DRIVER_DEBUG
+ bool "DAX: driver debug"
+ help
+ Enable validation of the page frame objects returned from a
+ driver's 'direct_access' operation. This validation is
+ performed relative to the requirements of the FS_DAX and
+ FS_DAX_LIMITED configuration options. If you are validating
+ the implementation of a dax device driver say Y otherwise
+ say N.
+
config DEV_DAX
tristate "Device DAX: direct access mapping device"
depends on TRANSPARENT_HUGEPAGE
diff --git a/drivers/dax/super.c b/drivers/dax/super.c
index 903d9c473749..87b1c55b7c7a 100644
--- a/drivers/dax/super.c
+++ b/drivers/dax/super.c
@@ -72,6 +72,41 @@ struct dax_device *fs_dax_get_by_bdev(struct block_device *bdev)
EXPORT_SYMBOL_GPL(fs_dax_get_by_bdev);
#endif
+static bool validate_dax_pfn(pfn_t *pfn)
+{
+ bool dax_enabled = false;
+
+ /*
+ * Unless debugging a new dax driver, or new dax architecture
+ * support there is no need to check the pfn. Delay the kernel's
+ * first need for a dax pfn until first userspace dax fault.
+ */
+ if (!pfn)
+ return true;
+
+ if (IS_ENABLED(CONFIG_FS_DAX_LIMITED) && pfn_t_special(*pfn)) {
+ /*
+ * An arch that has enabled the pmem api should also
+ * have its drivers support pfn_t_devmap()
+ *
+ * This is a developer warning and should not trigger in
+ * production. dax_flush() will crash since it depends
+ * on being able to do (page_address(pfn_to_page())).
+ */
+ WARN_ON(IS_ENABLED(CONFIG_ARCH_HAS_PMEM_API));
+ dax_enabled = true;
+ } else if (pfn_t_devmap(*pfn)) {
+ struct dev_pagemap *pgmap;
+
+ pgmap = get_dev_pagemap(pfn_t_to_pfn(*pfn), NULL);
+ if (pgmap && pgmap->type == MEMORY_DEVICE_FS_DAX)
+ dax_enabled = true;
+ put_dev_pagemap(pgmap);
+ }
+
+ return dax_enabled;
+}
+
/**
* __bdev_dax_supported() - Check if the device supports dax for filesystem
* @bdev: block device to check
@@ -85,11 +120,10 @@ EXPORT_SYMBOL_GPL(fs_dax_get_by_bdev);
bool __bdev_dax_supported(struct block_device *bdev, int blocksize)
{
struct dax_device *dax_dev;
- bool dax_enabled = false;
+ pfn_t _pfn, *pfn;
pgoff_t pgoff;
int err, id;
void *kaddr;
- pfn_t pfn;
long len;
char buf[BDEVNAME_SIZE];
@@ -113,8 +147,10 @@ bool __bdev_dax_supported(struct block_device *bdev, int blocksize)
return false;
}
+ pfn = IS_ENABLED(DAX_DRIVER_DEBUG) ? &_pfn : NULL;
+
id = dax_read_lock();
- len = dax_direct_access(dax_dev, pgoff, 1, &kaddr, &pfn);
+ len = dax_direct_access(dax_dev, pgoff, 1, &kaddr, pfn);
dax_read_unlock(id);
put_dax(dax_dev);
@@ -125,27 +161,7 @@ bool __bdev_dax_supported(struct block_device *bdev, int blocksize)
return false;
}
- if (IS_ENABLED(CONFIG_FS_DAX_LIMITED) && pfn_t_special(pfn)) {
- /*
- * An arch that has enabled the pmem api should also
- * have its drivers support pfn_t_devmap()
- *
- * This is a developer warning and should not trigger in
- * production. dax_flush() will crash since it depends
- * on being able to do (page_address(pfn_to_page())).
- */
- WARN_ON(IS_ENABLED(CONFIG_ARCH_HAS_PMEM_API));
- dax_enabled = true;
- } else if (pfn_t_devmap(pfn)) {
- struct dev_pagemap *pgmap;
-
- pgmap = get_dev_pagemap(pfn_t_to_pfn(pfn), NULL);
- if (pgmap && pgmap->type == MEMORY_DEVICE_FS_DAX)
- dax_enabled = true;
- put_dev_pagemap(pgmap);
- }
-
- if (!dax_enabled) {
+ if (!validate_dax_pfn(pfn)) {
pr_debug("%s: error: dax support not enabled\n",
bdevname(bdev, buf));
return false;
