bcache: A block layer cache
Does writethrough and writeback caching, handles unclean shutdown, and has a bunch of other nifty features motivated by real world usage. See the wiki at http://bcache.evilpiepirate.org for more. Signed-off-by: Kent Overstreet <koverstreet@google.com>
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Kent Overstreet
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Documentation/ABI/testing/sysfs-block-bcache
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Documentation/ABI/testing/sysfs-block-bcache
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What: /sys/block/<disk>/bcache/unregister
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Date: November 2010
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Contact: Kent Overstreet <kent.overstreet@gmail.com>
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Description:
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A write to this file causes the backing device or cache to be
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unregistered. If a backing device had dirty data in the cache,
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writeback mode is automatically disabled and all dirty data is
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flushed before the device is unregistered. Caches unregister
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all associated backing devices before unregistering themselves.
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What: /sys/block/<disk>/bcache/clear_stats
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Date: November 2010
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Contact: Kent Overstreet <kent.overstreet@gmail.com>
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Description:
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Writing to this file resets all the statistics for the device.
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What: /sys/block/<disk>/bcache/cache
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Date: November 2010
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Contact: Kent Overstreet <kent.overstreet@gmail.com>
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Description:
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For a backing device that has cache, a symlink to
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the bcache/ dir of that cache.
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What: /sys/block/<disk>/bcache/cache_hits
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Date: November 2010
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Contact: Kent Overstreet <kent.overstreet@gmail.com>
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Description:
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For backing devices: integer number of full cache hits,
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counted per bio. A partial cache hit counts as a miss.
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What: /sys/block/<disk>/bcache/cache_misses
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Date: November 2010
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Contact: Kent Overstreet <kent.overstreet@gmail.com>
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Description:
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For backing devices: integer number of cache misses.
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What: /sys/block/<disk>/bcache/cache_hit_ratio
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Date: November 2010
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Contact: Kent Overstreet <kent.overstreet@gmail.com>
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Description:
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For backing devices: cache hits as a percentage.
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What: /sys/block/<disk>/bcache/sequential_cutoff
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Date: November 2010
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Contact: Kent Overstreet <kent.overstreet@gmail.com>
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Description:
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For backing devices: Threshold past which sequential IO will
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skip the cache. Read and written as bytes in human readable
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units (i.e. echo 10M > sequntial_cutoff).
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What: /sys/block/<disk>/bcache/bypassed
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Date: November 2010
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Contact: Kent Overstreet <kent.overstreet@gmail.com>
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Description:
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Sum of all reads and writes that have bypassed the cache (due
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to the sequential cutoff). Expressed as bytes in human
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readable units.
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What: /sys/block/<disk>/bcache/writeback
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Date: November 2010
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Contact: Kent Overstreet <kent.overstreet@gmail.com>
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Description:
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For backing devices: When on, writeback caching is enabled and
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writes will be buffered in the cache. When off, caching is in
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writethrough mode; reads and writes will be added to the
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cache but no write buffering will take place.
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What: /sys/block/<disk>/bcache/writeback_running
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Date: November 2010
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Contact: Kent Overstreet <kent.overstreet@gmail.com>
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Description:
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For backing devices: when off, dirty data will not be written
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from the cache to the backing device. The cache will still be
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used to buffer writes until it is mostly full, at which point
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writes transparently revert to writethrough mode. Intended only
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for benchmarking/testing.
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What: /sys/block/<disk>/bcache/writeback_delay
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Date: November 2010
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Contact: Kent Overstreet <kent.overstreet@gmail.com>
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Description:
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For backing devices: In writeback mode, when dirty data is
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written to the cache and the cache held no dirty data for that
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backing device, writeback from cache to backing device starts
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after this delay, expressed as an integer number of seconds.
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What: /sys/block/<disk>/bcache/writeback_percent
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Date: November 2010
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Contact: Kent Overstreet <kent.overstreet@gmail.com>
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Description:
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For backing devices: If nonzero, writeback from cache to
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backing device only takes place when more than this percentage
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of the cache is used, allowing more write coalescing to take
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place and reducing total number of writes sent to the backing
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device. Integer between 0 and 40.
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What: /sys/block/<disk>/bcache/synchronous
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Date: November 2010
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Contact: Kent Overstreet <kent.overstreet@gmail.com>
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Description:
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For a cache, a boolean that allows synchronous mode to be
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switched on and off. In synchronous mode all writes are ordered
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such that the cache can reliably recover from unclean shutdown;
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if disabled bcache will not generally wait for writes to
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complete but if the cache is not shut down cleanly all data
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will be discarded from the cache. Should not be turned off with
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writeback caching enabled.
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What: /sys/block/<disk>/bcache/discard
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Date: November 2010
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Contact: Kent Overstreet <kent.overstreet@gmail.com>
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Description:
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For a cache, a boolean allowing discard/TRIM to be turned off
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or back on if the device supports it.
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What: /sys/block/<disk>/bcache/bucket_size
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Date: November 2010
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Contact: Kent Overstreet <kent.overstreet@gmail.com>
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Description:
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For a cache, bucket size in human readable units, as set at
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cache creation time; should match the erase block size of the
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SSD for optimal performance.
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What: /sys/block/<disk>/bcache/nbuckets
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Date: November 2010
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Contact: Kent Overstreet <kent.overstreet@gmail.com>
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Description:
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For a cache, the number of usable buckets.
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What: /sys/block/<disk>/bcache/tree_depth
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Date: November 2010
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Contact: Kent Overstreet <kent.overstreet@gmail.com>
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Description:
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For a cache, height of the btree excluding leaf nodes (i.e. a
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one node tree will have a depth of 0).
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What: /sys/block/<disk>/bcache/btree_cache_size
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Date: November 2010
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Contact: Kent Overstreet <kent.overstreet@gmail.com>
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Description:
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Number of btree buckets/nodes that are currently cached in
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memory; cache dynamically grows and shrinks in response to
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memory pressure from the rest of the system.
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What: /sys/block/<disk>/bcache/written
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Date: November 2010
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Contact: Kent Overstreet <kent.overstreet@gmail.com>
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Description:
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For a cache, total amount of data in human readable units
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written to the cache, excluding all metadata.
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What: /sys/block/<disk>/bcache/btree_written
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Date: November 2010
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Contact: Kent Overstreet <kent.overstreet@gmail.com>
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Description:
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For a cache, sum of all btree writes in human readable units.
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