Hi, Jens Redundant data is used to enhance data fault tolerance, and the storage method for redundant data vary depending on the RAID levels. And it's important to maintain the consistency of redundant data. Bitmap is used to record which data blocks have been synchronized and which ones need to be resynchronized or recovered. Each bit in the bitmap represents a segment of data in the array. When a bit is set, it indicates that the multiple redundant copies of that data segment may not be consistent. Data synchronization can be performed based on the bitmap after power failure or readding a disk. If there is no bitmap, a full disk synchronization is required. Due to known performance issues with md-bitmap and the unreasonable implementations: - self-managed IO submitting like filemap_write_page(); - global spin_lock - ... I have decided not to continue optimizing based on the current bitmap implementation, this new bitmap is invented without locking from IO fast path and can be used with fast disks. Key features for the new bitmap: - IO fastpath is lockless, if user issues lots of write IO to the same bitmap bit in a short time, only the first write has additional overhead to update bitmap bit, no additional overhead for the following writes; - support only resync or recover written data, means in the case creating new array or replacing with a new disk, there is no need to do a full disk resync/recovery; Please consider pulling following changes on your for-6.18/block branch, this pull request contains: - add kconfig for internal bitmap, this is for isolation; - introduce new experimental feature lockless bitmap(details in [1]); [1] https://lore.kernel.org/linux-raid/20250829080426.1441678-12-yukuai1@xxxxxxxxxxxxxxx/ The following changes since commit ba28afbd9eff2a6370f23ef4e6a036ab0cfda409: blk-mq: fix blk_mq_tags double free while nr_requests grown (2025-09-05 13:52:52 -0600) are available in the Git repository at: git@xxxxxxxxxxxxxxxxxxx:pub/scm/linux/kernel/git/mdraid/linux.git tags/md-6.18-20250909 for you to fetch changes up to 5ab829f1971dc99f2aac10846c378e67fc875abc: md/md-llbitmap: introduce new lockless bitmap (2025-09-06 17:27:51 +0800) ---------------------------------------------------------------- Yu Kuai (24): md/md-bitmap: remove the parameter 'init' for bitmap_ops->resize() md/md-bitmap: merge md_bitmap_group into bitmap_operations md/md-bitmap: add a new parameter 'flush' to bitmap_ops->enabled md/md-bitmap: add md_bitmap_registered/enabled() helper md/md-bitmap: handle the case bitmap is not enabled before start_sync() md/md-bitmap: handle the case bitmap is not enabled before end_sync() md/raid1: check bitmap before behind write md/raid1: check before referencing mddev->bitmap_ops md/raid10: check before referencing mddev->bitmap_ops md/raid5: check before referencing mddev->bitmap_ops md/dm-raid: check before referencing mddev->bitmap_ops md: check before referencing mddev->bitmap_ops md/md-bitmap: introduce CONFIG_MD_BITMAP md: add a new parameter 'offset' to md_super_write() md: factor out a helper raid_is_456() md/md-bitmap: support discard for bitmap ops md: add a new mddev field 'bitmap_id' md/md-bitmap: add a new sysfs api bitmap_type md/md-bitmap: delay registration of bitmap_ops until creating bitmap md/md-bitmap: add a new method skip_sync_blocks() in bitmap_operations md/md-bitmap: add a new method blocks_synced() in bitmap_operations md: add a new recovery_flag MD_RECOVERY_LAZY_RECOVER md/md-bitmap: make method bitmap_ops->daemon_work optional md/md-llbitmap: introduce new lockless bitmap Documentation/admin-guide/md.rst | 86 +++- drivers/md/Kconfig | 29 ++ drivers/md/Makefile | 4 +- drivers/md/dm-raid.c | 18 +- drivers/md/md-bitmap.c | 89 ++-- drivers/md/md-bitmap.h | 107 ++++- drivers/md/md-cluster.c | 2 +- drivers/md/md-llbitmap.c | 1626 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ drivers/md/md.c | 378 ++++++++++++--- drivers/md/md.h | 24 +- drivers/md/raid1-10.c | 2 +- drivers/md/raid1.c | 79 ++-- drivers/md/raid10.c | 49 +- drivers/md/raid5.c | 64 ++- 14 files changed, 2313 insertions(+), 244 deletions(-) create mode 100644 drivers/md/md-llbitmap.c
