kernel/drivers/block/null_blk.h, branch linux-6.9.y

null_blk: Move driver into its own directory

2020-12-08T00:36:04Z

Move null_blk driver code into the new sub-directory drivers/block/null_blk. Suggested-by: Bart Van Assche Signed-off-by: Damien Le Moal Reviewed-by: Johannes Thumshirn Signed-off-by: Jens Axboe

null_blk: Allow controlling max_hw_sectors limit

2020-12-08T00:36:04Z

Add the module option and configfs attribute max_sectors to allow configuring the maximum size of a command issued to a null_blk device. This allows exercising the block layer BIO splitting with different limits than the default BLK_SAFE_MAX_SECTORS. This is also useful for testing the zone append write path of file systems as the max_hw_sectors limit value is also used for the max_zone_append_sectors limit. Signed-off-by: Damien Le Moal Reviewed-by: Christoph Hellwig Reviewed-by: Johannes Thumshirn Signed-off-by: Jens Axboe

null_blk: discard zones on reset

2020-12-08T00:36:03Z

When memory backing is enabled, use null_handle_discard() to free the backing memory used by a zone when the zone is being reset. Signed-off-by: Damien Le Moal Reviewed-by: Christoph Hellwig Reviewed-by: Johannes Thumshirn Signed-off-by: Jens Axboe

null_blk: Improve implicit zone close

2020-12-08T00:36:03Z

When open zone resource management is enabled, that is, when a null_blk zoned device is created with zone_max_open different than 0, implicitly or explicitly opening a zone may require implicitly closing a zone that is already implicitly open. This operation is done using the function null_close_first_imp_zone(), which search for an implicitly open zone to close starting from the first sequential zone. This implementation is simple but may result in the same being constantly implicitly closed and then implicitly reopened on write, namely, the lowest numbered zone that is being written. Avoid this by starting the search for an implicitly open zone starting from the zone following the last zone that was implicitly closed. The function null_close_first_imp_zone() is renamed null_close_imp_open_zone(). Signed-off-by: Damien Le Moal Reviewed-by: Johannes Thumshirn Signed-off-by: Jens Axboe

null_blk: improve zone locking

2020-12-08T00:36:03Z

With memory backing disabled, using a single spinlock for protecting zone information and zone resource management prevents the parallel execution on multiple queue of IO requests to different zones. Furthermore, regardless of the use of memory backing, if a null_blk device is created without limits on the number of open and active zones, accounting for zone resource management is not necessary. >From these observations, zone locking is changed as follows to improve performance: 1) the zone_lock spinlock is renamed zone_res_lock and used only if zone resource management is necessary, that is, if either zone_max_open or zone_max_active are not 0. This is indicated using the new boolean need_zone_res_mgmt in the nullb_device structure. null_zone_write() is modified to reduce the amount of code executed with the zone_res_lock spinlock held. 2) With memory backing disabled, per zone locking is changed to a spinlock per zone. 3) Introduce the structure nullb_zone to replace the use of struct blk_zone for zone information. This new structure includes a union of a spinlock and a mutex for zone locking. The spinlock is used when memory backing is disabled and the mutex is used with memory backing. With these changes, fio performance with zonemode=zbd for 4K random read and random write on a dual socket (24 cores per socket) machine using the none schedulder is as follows: before patch: write (psync x 96 jobs) = 465 KIOPS read (libaio@qd=8 x 96 jobs) = 1361 KIOPS after patch: write (psync x 96 jobs) = 456 KIOPS read (libaio@qd=8 x 96 jobs) = 4096 KIOPS Write performance remains mostly unchanged but read performance is three times higher. Performance when using the mq-deadline scheduler is not changed by this patch as mq-deadline becomes the bottleneck for a multi-queue device. Signed-off-by: Damien Le Moal Reviewed-by: Christoph Hellwig Reviewed-by: Johannes Thumshirn Signed-off-by: Jens Axboe

null_blk: Fix scheduling in atomic with zoned mode

2020-11-06T16:36:42Z

Commit aa1c09cb65e2 ("null_blk: Fix locking in zoned mode") changed zone locking to using the potentially sleeping wait_on_bit_io() function. This is acceptable when memory backing is enabled as the device queue is in that case marked as blocking, but this triggers a scheduling while in atomic context with memory backing disabled. Fix this by relying solely on the device zone spinlock for zone information protection without temporarily releasing this lock around null_process_cmd() execution in null_zone_write(). This is OK to do since when memory backing is disabled, command processing does not block and the memory backing lock nullb->lock is unused. This solution avoids the overhead of having to mark a zoned null_blk device queue as blocking when memory backing is unused. This patch also adds comments to the zone locking code to explain the unusual locking scheme. Fixes: aa1c09cb65e2 ("null_blk: Fix locking in zoned mode") Reported-by: kernel test robot Signed-off-by: Damien Le Moal Reviewed-by: Christoph Hellwig Cc: stable@vger.kernel.org Signed-off-by: Jens Axboe

null_blk: Fix locking in zoned mode

2020-10-29T13:27:30Z

When the zoned mode is enabled in null_blk, Serializing read, write and zone management operations for each zone is necessary to protect device level information for managing zone resources (zone open and closed counters) as well as each zone condition and write pointer position. Commit 35bc10b2eafb ("null_blk: synchronization fix for zoned device") introduced a spinlock to implement this serialization. However, when memory backing is also enabled, GFP_NOIO memory allocations are executed under the spinlock, resulting in might_sleep() warnings. Furthermore, the zone_lock spinlock is locked/unlocked using spin_lock_irq/spin_unlock_irq, similarly to the memory backing code with the nullb->lock spinlock. This nested use of irq locks wrecks the irq enabled/disabled state. Fix all this by introducing a bitmap for per-zone lock, with locking implemented using wait_on_bit_lock_io() and clear_and_wake_up_bit(). This locking mechanism allows keeping a zone locked while executing null_process_cmd(), serializing all operations to the zone while allowing to sleep during memory backing allocation with GFP_NOIO. Device level zone resource management information is protected using a spinlock which is not held while executing null_process_cmd(); Fixes: 35bc10b2eafb ("null_blk: synchronization fix for zoned device") Signed-off-by: Damien Le Moal Signed-off-by: Jens Axboe

null_blk: synchronization fix for zoned device

2020-10-28T02:40:42Z

Parallel write,read,zone-mgmt operations accessing/altering zone state and write-pointer may get into race. Avoid the situation by using a new spinlock for zoned device. Concurrent zone-appends (on a zone) returning same write-pointer issue is also avoided using this lock. Cc: stable@vger.kernel.org Fixes: e0489ed5daeb ("null_blk: Support REQ_OP_ZONE_APPEND") Signed-off-by: Kanchan Joshi Reviewed-by: Damien Le Moal Signed-off-by: Jens Axboe

null_blk: add support for max open/active zone limit for zoned devices

2020-09-29T14:12:48Z

Add support for user space to set a max open zone and a max active zone limit via configfs. By default, the default values are 0 == no limit. Call the block layer API functions used for exposing the configured limits to sysfs. Add accounting in null_blk_zoned so that these new limits are respected. Performing an operation that would exceed these limits results in a standard I/O error. A max open zone limit exists in the ZBC standard. While null_blk_zoned is used to test the Zoned Block Device model in Linux, when it comes to differences between ZBC and ZNS, null_blk_zoned mostly follows ZBC. Therefore, implement the manage open zone resources function from ZBC, but additionally add support for max active zones. This enables user space not only to test against a device with an open zone limit, but also to test against a device with an active zone limit. Signed-off-by: Niklas Cassel Reviewed-by: Damien Le Moal Reviewed-by: Johannes Thumshirn Signed-off-by: Jens Axboe

null_blk: introduce zone capacity for zoned device

2020-07-08T14:16:19Z

Allow emulation of a zoned device with a per zone capacity smaller than the zone size as as defined in the Zoned Namespace (ZNS) Command Set specification. The zone capacity defaults to the zone size if not specified and must be smaller than the zone size otherwise. Reviewed-by: Matias Bjørling Reviewed-by: Chaitanya Kulkarni Reviewed-by: Himanshu Madhani Reviewed-by: Martin K. Petersen Reviewed-by: Hannes Reinecke Reviewed-by: Johannes Thumshirn Reviewed-by: Daniel Wagner Signed-off-by: Aravind Ramesh Signed-off-by: Christoph Hellwig