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 <[email protected]> Cc: Christoph Hellwig <[email protected]> Cc: Ross Zwisler <[email protected]> Signed-off-by: Dan Williams <[email protected]> --- 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; _______________________________________________ Linux-nvdimm mailing list [email protected] https://lists.01.org/mailman/listinfo/linux-nvdimm
