Merge branch 'bcache-for-upstream' of... (e226e341) · Commits · e / devices / android_kernel_fairphone_FP5

Documentation/ABI/testing/sysfs-block-bcache

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		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.

Documentation/bcache.txt

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		Say you've got a big slow raid 6, and an X-25E or three. Wouldn't it be
		nice if you could use them as cache... Hence bcache.

		Wiki and git repositories are at:
		http://bcache.evilpiepirate.org
		http://evilpiepirate.org/git/linux-bcache.git
		http://evilpiepirate.org/git/bcache-tools.git

		It's designed around the performance characteristics of SSDs - it only allocates
		in erase block sized buckets, and it uses a hybrid btree/log to track cached
		extants (which can be anywhere from a single sector to the bucket size). It's
		designed to avoid random writes at all costs; it fills up an erase block
		sequentially, then issues a discard before reusing it.

		Both writethrough and writeback caching are supported. Writeback defaults to
		off, but can be switched on and off arbitrarily at runtime. Bcache goes to
		great lengths to protect your data - it reliably handles unclean shutdown. (It
		doesn't even have a notion of a clean shutdown; bcache simply doesn't return
		writes as completed until they're on stable storage).

		Writeback caching can use most of the cache for buffering writes - writing
		dirty data to the backing device is always done sequentially, scanning from the
		start to the end of the index.

		Since random IO is what SSDs excel at, there generally won't be much benefit
		to caching large sequential IO. Bcache detects sequential IO and skips it;
		it also keeps a rolling average of the IO sizes per task, and as long as the
		average is above the cutoff it will skip all IO from that task - instead of
		caching the first 512k after every seek. Backups and large file copies should
		thus entirely bypass the cache.

		In the event of a data IO error on the flash it will try to recover by reading
		from disk or invalidating cache entries. For unrecoverable errors (meta data
		or dirty data), caching is automatically disabled; if dirty data was present
		in the cache it first disables writeback caching and waits for all dirty data
		to be flushed.

		Getting started:
		You'll need make-bcache from the bcache-tools repository. Both the cache device
		and backing device must be formatted before use.
		make-bcache -B /dev/sdb
		make-bcache -C /dev/sdc

		make-bcache has the ability to format multiple devices at the same time - if
		you format your backing devices and cache device at the same time, you won't
		have to manually attach:
		make-bcache -B /dev/sda /dev/sdb -C /dev/sdc

		To make bcache devices known to the kernel, echo them to /sys/fs/bcache/register:

		echo /dev/sdb > /sys/fs/bcache/register
		echo /dev/sdc > /sys/fs/bcache/register

		To register your bcache devices automatically, you could add something like
		this to an init script:

		echo /dev/sd* > /sys/fs/bcache/register_quiet

		It'll look for bcache superblocks and ignore everything that doesn't have one.

		Registering the backing device makes the bcache show up in /dev; you can now
		format it and use it as normal. But the first time using a new bcache device,
		it'll be running in passthrough mode until you attach it to a cache. See the
		section on attaching.

		The devices show up at /dev/bcacheN, and can be controlled via sysfs from
		/sys/block/bcacheN/bcache:

		mkfs.ext4 /dev/bcache0
		mount /dev/bcache0 /mnt

		Cache devices are managed as sets; multiple caches per set isn't supported yet
		but will allow for mirroring of metadata and dirty data in the future. Your new
		cache set shows up as /sys/fs/bcache/<UUID>

		ATTACHING:

		After your cache device and backing device are registered, the backing device
		must be attached to your cache set to enable caching. Attaching a backing
		device to a cache set is done thusly, with the UUID of the cache set in
		/sys/fs/bcache:

		echo <UUID> > /sys/block/bcache0/bcache/attach

		This only has to be done once. The next time you reboot, just reregister all
		your bcache devices. If a backing device has data in a cache somewhere, the
		/dev/bcache# device won't be created until the cache shows up - particularly
		important if you have writeback caching turned on.

		If you're booting up and your cache device is gone and never coming back, you
		can force run the backing device:

		echo 1 > /sys/block/sdb/bcache/running

		(You need to use /sys/block/sdb (or whatever your backing device is called), not
		/sys/block/bcache0, because bcache0 doesn't exist yet. If you're using a
		partition, the bcache directory would be at /sys/block/sdb/sdb2/bcache)

		The backing device will still use that cache set if it shows up in the future,
		but all the cached data will be invalidated. If there was dirty data in the
		cache, don't expect the filesystem to be recoverable - you will have massive
		filesystem corruption, though ext4's fsck does work miracles.

		SYSFS - BACKING DEVICE:

		attach
		Echo the UUID of a cache set to this file to enable caching.

		cache_mode
		Can be one of either writethrough, writeback, writearound or none.

		clear_stats
		Writing to this file resets the running total stats (not the day/hour/5 minute
		decaying versions).

		detach
		Write to this file to detach from a cache set. If there is dirty data in the
		cache, it will be flushed first.

		dirty_data
		Amount of dirty data for this backing device in the cache. Continuously
		updated unlike the cache set's version, but may be slightly off.

		label
		Name of underlying device.

		readahead
		Size of readahead that should be performed. Defaults to 0. If set to e.g.
		1M, it will round cache miss reads up to that size, but without overlapping
		existing cache entries.

		running
		1 if bcache is running (i.e. whether the /dev/bcache device exists, whether
		it's in passthrough mode or caching).

		sequential_cutoff
		A sequential IO will bypass the cache once it passes this threshhold; the
		most recent 128 IOs are tracked so sequential IO can be detected even when
		it isn't all done at once.

		sequential_merge
		If non zero, bcache keeps a list of the last 128 requests submitted to compare
		against all new requests to determine which new requests are sequential
		continuations of previous requests for the purpose of determining sequential
		cutoff. This is necessary if the sequential cutoff value is greater than the
		maximum acceptable sequential size for any single request.

		state
		The backing device can be in one of four different states:

		no cache: Has never been attached to a cache set.

		clean: Part of a cache set, and there is no cached dirty data.

		dirty: Part of a cache set, and there is cached dirty data.

		inconsistent: The backing device was forcibly run by the user when there was
		dirty data cached but the cache set was unavailable; whatever data was on the
		backing device has likely been corrupted.

		stop
		Write to this file to shut down the bcache device and close the backing
		device.

		writeback_delay
		When dirty data is written to the cache and it previously did not contain
		any, waits some number of seconds before initiating writeback. Defaults to
		30.

		writeback_percent
		If nonzero, bcache tries to keep around this percentage of the cache dirty by
		throttling background writeback and using a PD controller to smoothly adjust
		the rate.

		writeback_rate
		Rate in sectors per second - if writeback_percent is nonzero, background
		writeback is throttled to this rate. Continuously adjusted by bcache but may
		also be set by the user.

		writeback_running
		If off, writeback of dirty data will not take place at all. Dirty data will
		still be added to the cache until it is mostly full; only meant for
		benchmarking. Defaults to on.

		SYSFS - BACKING DEVICE STATS:

		There are directories with these numbers for a running total, as well as
		versions that decay over the past day, hour and 5 minutes; they're also
		aggregated in the cache set directory as well.

		bypassed
		Amount of IO (both reads and writes) that has bypassed the cache

		cache_hits
		cache_misses
		cache_hit_ratio
		Hits and misses are counted per individual IO as bcache sees them; a
		partial hit is counted as a miss.

		cache_bypass_hits
		cache_bypass_misses
		Hits and misses for IO that is intended to skip the cache are still counted,
		but broken out here.

		cache_miss_collisions
		Counts instances where data was going to be inserted into the cache from a
		cache miss, but raced with a write and data was already present (usually 0
		since the synchronization for cache misses was rewritten)

		cache_readaheads
		Count of times readahead occured.

		SYSFS - CACHE SET:

		average_key_size
		Average data per key in the btree.

		bdev<0..n>
		Symlink to each of the attached backing devices.

		block_size
		Block size of the cache devices.

		btree_cache_size
		Amount of memory currently used by the btree cache

		bucket_size
		Size of buckets

		cache<0..n>
		Symlink to each of the cache devices comprising this cache set.

		cache_available_percent
		Percentage of cache device free.

		clear_stats
		Clears the statistics associated with this cache

		dirty_data
		Amount of dirty data is in the cache (updated when garbage collection runs).

		flash_vol_create
		Echoing a size to this file (in human readable units, k/M/G) creates a thinly
		provisioned volume backed by the cache set.

		io_error_halflife
		io_error_limit
		These determines how many errors we accept before disabling the cache.
		Each error is decayed by the half life (in # ios). If the decaying count
		reaches io_error_limit dirty data is written out and the cache is disabled.

		journal_delay_ms
		Journal writes will delay for up to this many milliseconds, unless a cache
		flush happens sooner. Defaults to 100.

		root_usage_percent
		Percentage of the root btree node in use. If this gets too high the node
		will split, increasing the tree depth.

		stop
		Write to this file to shut down the cache set - waits until all attached
		backing devices have been shut down.

		tree_depth
		Depth of the btree (A single node btree has depth 0).

		unregister
		Detaches all backing devices and closes the cache devices; if dirty data is
		present it will disable writeback caching and wait for it to be flushed.

		SYSFS - CACHE SET INTERNAL:

		This directory also exposes timings for a number of internal operations, with
		separate files for average duration, average frequency, last occurence and max
		duration: garbage collection, btree read, btree node sorts and btree splits.

		active_journal_entries
		Number of journal entries that are newer than the index.

		btree_nodes
		Total nodes in the btree.

		btree_used_percent
		Average fraction of btree in use.

		bset_tree_stats
		Statistics about the auxiliary search trees

		btree_cache_max_chain
		Longest chain in the btree node cache's hash table

		cache_read_races
		Counts instances where while data was being read from the cache, the bucket
		was reused and invalidated - i.e. where the pointer was stale after the read
		completed. When this occurs the data is reread from the backing device.

		trigger_gc
		Writing to this file forces garbage collection to run.

		SYSFS - CACHE DEVICE:

		block_size
		Minimum granularity of writes - should match hardware sector size.

		btree_written
		Sum of all btree writes, in (kilo/mega/giga) bytes

		bucket_size
		Size of buckets

		cache_replacement_policy
		One of either lru, fifo or random.

		discard
		Boolean; if on a discard/TRIM will be issued to each bucket before it is
		reused. Defaults to off, since SATA TRIM is an unqueued command (and thus
		slow).

		freelist_percent
		Size of the freelist as a percentage of nbuckets. Can be written to to
		increase the number of buckets kept on the freelist, which lets you
		artificially reduce the size of the cache at runtime. Mostly for testing
		purposes (i.e. testing how different size caches affect your hit rate), but
		since buckets are discarded when they move on to the freelist will also make
		the SSD's garbage collection easier by effectively giving it more reserved
		space.

		io_errors
		Number of errors that have occured, decayed by io_error_halflife.

		metadata_written
		Sum of all non data writes (btree writes and all other metadata).

		nbuckets
		Total buckets in this cache

		priority_stats
		Statistics about how recently data in the cache has been accessed. This can
		reveal your working set size.

		written
		Sum of all data that has been written to the cache; comparison with
		btree_written gives the amount of write inflation in bcache.

MAINTAINERS

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		@@ -1616,6 +1616,13 @@ W: http://www.baycom.org/~tom/ham/ham.html
		S: Maintained
		F: drivers/net/hamradio/baycom*

		BCACHE (BLOCK LAYER CACHE)
		M: Kent Overstreet <koverstreet@google.com>
		L: linux-bcache@vger.kernel.org
		W: http://bcache.evilpiepirate.org
		S: Maintained:
		F: drivers/md/bcache/

		BEFS FILE SYSTEM
		S: Orphan
		F: Documentation/filesystems/befs.txt

drivers/char/random.c

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		@@ -1485,6 +1485,7 @@ unsigned int get_random_int(void)

		return ret;
		}
		EXPORT_SYMBOL(get_random_int);

		/*
		* randomize_range() returns a start address such that

drivers/md/Kconfig

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		@@ -174,6 +174,8 @@ config MD_FAULTY

		In unsure, say N.

		source "drivers/md/bcache/Kconfig"

		config BLK_DEV_DM
		tristate "Device mapper support"
		---help---