xref: /kernel/linux/linux-6.6/Documentation/ABI/testing/sysfs-block-bcache

What:		/sys/block/<disk>/bcache/unregister
Date:		November 2010
Contact:	Kent Overstreet <kent.overstreet@gmail.com>
Description:
		A write to this file causes the backing device or cache to be
		unregistered. If a backing device had dirty data in the cache,
		writeback mode is automatically disabled and all dirty data is
		flushed before the device is unregistered. Caches unregister
		all associated backing devices before unregistering themselves.

What:		/sys/block/<disk>/bcache/clear_stats
Date:		November 2010
Contact:	Kent Overstreet <kent.overstreet@gmail.com>
Description:
		Writing to this file resets all the statistics for the device.

What:		/sys/block/<disk>/bcache/cache
Date:		November 2010
Contact:	Kent Overstreet <kent.overstreet@gmail.com>
Description:
		For a backing device that has cache, a symlink to
		the bcache/ dir of that cache.

What:		/sys/block/<disk>/bcache/cache_hits
Date:		November 2010
Contact:	Kent Overstreet <kent.overstreet@gmail.com>
Description:
		For backing devices: integer number of full cache hits,
		counted per bio. A partial cache hit counts as a miss.

What:		/sys/block/<disk>/bcache/cache_misses
Date:		November 2010
Contact:	Kent Overstreet <kent.overstreet@gmail.com>
Description:
		For backing devices: integer number of cache misses.

What:		/sys/block/<disk>/bcache/cache_hit_ratio
Date:		November 2010
Contact:	Kent Overstreet <kent.overstreet@gmail.com>
Description:
		For backing devices: cache hits as a percentage.

What:		/sys/block/<disk>/bcache/sequential_cutoff
Date:		November 2010
Contact:	Kent Overstreet <kent.overstreet@gmail.com>
Description:
		For backing devices: Threshold past which sequential IO will
		skip the cache. Read and written as bytes in human readable
		units (i.e. echo 10M > sequntial_cutoff).

What:		/sys/block/<disk>/bcache/bypassed
Date:		November 2010
Contact:	Kent Overstreet <kent.overstreet@gmail.com>
Description:
		Sum of all reads and writes that have bypassed the cache (due
		to the sequential cutoff).  Expressed as bytes in human
		readable units.

What:		/sys/block/<disk>/bcache/writeback
Date:		November 2010
Contact:	Kent Overstreet <kent.overstreet@gmail.com>
Description:
		For backing devices: When on, writeback caching is enabled and
		writes will be buffered in the cache. When off, caching is in
		writethrough mode; reads and writes will be added to the
		cache but no write buffering will take place.

What:		/sys/block/<disk>/bcache/writeback_running
Date:		November 2010
Contact:	Kent Overstreet <kent.overstreet@gmail.com>
Description:
		For backing devices: when off, dirty data will not be written
		from the cache to the backing device. The cache will still be
		used to buffer writes until it is mostly full, at which point
		writes transparently revert to writethrough mode. Intended only
		for benchmarking/testing.

What:		/sys/block/<disk>/bcache/writeback_delay
Date:		November 2010
Contact:	Kent Overstreet <kent.overstreet@gmail.com>
Description:
		For backing devices: In writeback mode, when dirty data is
		written to the cache and the cache held no dirty data for that
		backing device, writeback from cache to backing device starts
		after this delay, expressed as an integer number of seconds.

What:		/sys/block/<disk>/bcache/writeback_percent
Date:		November 2010
Contact:	Kent Overstreet <kent.overstreet@gmail.com>
Description:
		For backing devices: If nonzero, writeback from cache to
		backing device only takes place when more than this percentage
		of the cache is used, allowing more write coalescing to take
		place and reducing total number of writes sent to the backing
		device. Integer between 0 and 40.

What:		/sys/block/<disk>/bcache/synchronous
Date:		November 2010
Contact:	Kent Overstreet <kent.overstreet@gmail.com>
Description:
		For a cache, a boolean that allows synchronous mode to be
		switched on and off. In synchronous mode all writes are ordered
		such that the cache can reliably recover from unclean shutdown;
		if disabled bcache will not generally wait for writes to
		complete but if the cache is not shut down cleanly all data
		will be discarded from the cache. Should not be turned off with
		writeback caching enabled.

What:		/sys/block/<disk>/bcache/discard
Date:		November 2010
Contact:	Kent Overstreet <kent.overstreet@gmail.com>
Description:
		For a cache, a boolean allowing discard/TRIM to be turned off
		or back on if the device supports it.

What:		/sys/block/<disk>/bcache/bucket_size
Date:		November 2010
Contact:	Kent Overstreet <kent.overstreet@gmail.com>
Description:
		For a cache, bucket size in human readable units, as set at
		cache creation time; should match the erase block size of the
		SSD for optimal performance.

What:		/sys/block/<disk>/bcache/nbuckets
Date:		November 2010
Contact:	Kent Overstreet <kent.overstreet@gmail.com>
Description:
		For a cache, the number of usable buckets.

What:		/sys/block/<disk>/bcache/tree_depth
Date:		November 2010
Contact:	Kent Overstreet <kent.overstreet@gmail.com>
Description:
		For a cache, height of the btree excluding leaf nodes (i.e. a
		one node tree will have a depth of 0).

What:		/sys/block/<disk>/bcache/btree_cache_size
Date:		November 2010
Contact:	Kent Overstreet <kent.overstreet@gmail.com>
Description:
		Number of btree buckets/nodes that are currently cached in
		memory; cache dynamically grows and shrinks in response to
		memory pressure from the rest of the system.

What:		/sys/block/<disk>/bcache/written
Date:		November 2010
Contact:	Kent Overstreet <kent.overstreet@gmail.com>
Description:
		For a cache, total amount of data in human readable units
		written to the cache, excluding all metadata.

What:		/sys/block/<disk>/bcache/btree_written
Date:		November 2010
Contact:	Kent Overstreet <kent.overstreet@gmail.com>
Description:
		For a cache, sum of all btree writes in human readable units.