[linux.git] / Documentation / filesystems / caching / fscache.txt

			  ==========================
			  General Filesystem Caching
			  ==========================

========
OVERVIEW
========

This facility is a general purpose cache for network filesystems, though it
could be used for caching other things such as ISO9660 filesystems too.

FS-Cache mediates between cache backends (such as CacheFS) and network
filesystems:

	+---------+
	|         |                        +--------------+
	|   NFS   |--+                     |              |
	|         |  |                 +-->|   CacheFS    |
	+---------+  |   +----------+  |   |  /dev/hda5   |
	             |   |          |  |   +--------------+
	+---------+  +-->|          |  |
	|         |      |          |--+
	|   AFS   |----->| FS-Cache |
	|         |      |          |--+
	+---------+  +-->|          |  |
	             |   |          |  |   +--------------+
	+---------+  |   +----------+  |   |              |
	|         |  |                 +-->|  CacheFiles  |
	|  ISOFS  |--+                     |  /var/cache  |
	|         |                        +--------------+
	+---------+

Or to look at it another way, FS-Cache is a module that provides a caching
facility to a network filesystem such that the cache is transparent to the
user:

	+---------+
	|         |
	| Server  |
	|         |
	+---------+
	     |                  NETWORK
	~~~~~|~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
	     |
	     |           +----------+
	     V           |          |
	+---------+      |          |
	|         |      |          |
	|   NFS   |----->| FS-Cache |
	|         |      |          |--+
	+---------+      |          |  |   +--------------+   +--------------+
	     |           |          |  |   |              |   |              |
	     V           +----------+  +-->|  CacheFiles  |-->|  Ext3        |
	+---------+                        |  /var/cache  |   |  /dev/sda6   |
	|         |                        +--------------+   +--------------+
	|   VFS   |                                ^                     ^
	|         |                                |                     |
	+---------+                                +--------------+      |
	     |                  KERNEL SPACE                      |      |
	~~~~~|~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~|~~~~~~|~~~~
	     |                  USER SPACE                        |      |
	     V                                                    |      |
	+---------+                                           +--------------+
	|         |                                           |              |
	| Process |                                           | cachefilesd  |
	|         |                                           |              |
	+---------+                                           +--------------+


FS-Cache does not follow the idea of completely loading every netfs file
opened in its entirety into a cache before permitting it to be accessed and
then serving the pages out of that cache rather than the netfs inode because:

 (1) It must be practical to operate without a cache.

 (2) The size of any accessible file must not be limited to the size of the
     cache.

 (3) The combined size of all opened files (this includes mapped libraries)
     must not be limited to the size of the cache.

 (4) The user should not be forced to download an entire file just to do a
     one-off access of a small portion of it (such as might be done with the
     "file" program).

It instead serves the cache out in PAGE_SIZE chunks as and when requested by
the netfs('s) using it.


FS-Cache provides the following facilities:

 (1) More than one cache can be used at once.  Caches can be selected
     explicitly by use of tags.

 (2) Caches can be added / removed at any time.

 (3) The netfs is provided with an interface that allows either party to
     withdraw caching facilities from a file (required for (2)).

 (4) The interface to the netfs returns as few errors as possible, preferring
     rather to let the netfs remain oblivious.

 (5) Cookies are used to represent indices, files and other objects to the
     netfs.  The simplest cookie is just a NULL pointer - indicating nothing
     cached there.

 (6) The netfs is allowed to propose - dynamically - any index hierarchy it
     desires, though it must be aware that the index search function is
     recursive, stack space is limited, and indices can only be children of
     indices.

 (7) Data I/O is done direct to and from the netfs's pages.  The netfs
     indicates that page A is at index B of the data-file represented by cookie
     C, and that it should be read or written.  The cache backend may or may
     not start I/O on that page, but if it does, a netfs callback will be
     invoked to indicate completion.  The I/O may be either synchronous or
     asynchronous.

 (8) Cookies can be "retired" upon release.  At this point FS-Cache will mark
     them as obsolete and the index hierarchy rooted at that point will get
     recycled.

 (9) The netfs provides a "match" function for index searches.  In addition to
     saying whether a match was made or not, this can also specify that an
     entry should be updated or deleted.

(10) As much as possible is done asynchronously.


FS-Cache maintains a virtual indexing tree in which all indices, files, objects
and pages are kept.  Bits of this tree may actually reside in one or more
caches.

                                           FSDEF
                                             |
                        +------------------------------------+
                        |                                    |
                       NFS                                  AFS
                        |                                    |
           +--------------------------+                +-----------+
           |                          |                |           |
        homedir                     mirror          afs.org   redhat.com
           |                          |                            |
     +------------+           +---------------+              +----------+
     |            |           |               |              |          |
   00001        00002       00007           00125        vol00001   vol00002
     |            |           |               |                         |
 +---+---+     +-----+      +---+      +------+------+            +-----+----+
 |   |   |     |     |      |   |      |      |      |            |     |    |
PG0 PG1 PG2   PG0  XATTR   PG0 PG1   DIRENT DIRENT DIRENT        R/W   R/O  Bak
                     |                                            |
                    PG0                                       +-------+
                                                              |       |
                                                            00001   00003
                                                              |
                                                          +---+---+
                                                          |   |   |
                                                         PG0 PG1 PG2

In the example above, you can see two netfs's being backed: NFS and AFS.  These
have different index hierarchies:

 (*) The NFS primary index contains per-server indices.  Each server index is
     indexed by NFS file handles to get data file objects.  Each data file
     objects can have an array of pages, but may also have further child
     objects, such as extended attributes and directory entries.  Extended
     attribute objects themselves have page-array contents.

 (*) The AFS primary index contains per-cell indices.  Each cell index contains
     per-logical-volume indices.  Each of volume index contains up to three
     indices for the read-write, read-only and backup mirrors of those volumes.
     Each of these contains vnode data file objects, each of which contains an
     array of pages.

The very top index is the FS-Cache master index in which individual netfs's
have entries.

Any index object may reside in more than one cache, provided it only has index
children.  Any index with non-index object children will be assumed to only
reside in one cache.


The netfs API to FS-Cache can be found in:

	Documentation/filesystems/caching/netfs-api.txt

The cache backend API to FS-Cache can be found in:

	Documentation/filesystems/caching/backend-api.txt

A description of the internal representations and object state machine can be
found in:

	Documentation/filesystems/caching/object.txt


=======================
STATISTICAL INFORMATION
=======================

If FS-Cache is compiled with the following options enabled:

	CONFIG_FSCACHE_STATS=y
	CONFIG_FSCACHE_HISTOGRAM=y

then it will gather certain statistics and display them through a number of
proc files.

 (*) /proc/fs/fscache/stats

     This shows counts of a number of events that can happen in FS-Cache:

	CLASS	EVENT	MEANING
	=======	=======	=======================================================
	Cookies	idx=N	Number of index cookies allocated
		dat=N	Number of data storage cookies allocated
		spc=N	Number of special cookies allocated
	Objects	alc=N	Number of objects allocated
		nal=N	Number of object allocation failures
		avl=N	Number of objects that reached the available state
		ded=N	Number of objects that reached the dead state
	ChkAux	non=N	Number of objects that didn't have a coherency check
		ok=N	Number of objects that passed a coherency check
		upd=N	Number of objects that needed a coherency data update
		obs=N	Number of objects that were declared obsolete
	Pages	mrk=N	Number of pages marked as being cached
		unc=N	Number of uncache page requests seen
	Acquire	n=N	Number of acquire cookie requests seen
		nul=N	Number of acq reqs given a NULL parent
		noc=N	Number of acq reqs rejected due to no cache available
		ok=N	Number of acq reqs succeeded
		nbf=N	Number of acq reqs rejected due to error
		oom=N	Number of acq reqs failed on ENOMEM
	Lookups	n=N	Number of lookup calls made on cache backends
		neg=N	Number of negative lookups made
		pos=N	Number of positive lookups made
		crt=N	Number of objects created by lookup
		tmo=N	Number of lookups timed out and requeued
	Updates	n=N	Number of update cookie requests seen
		nul=N	Number of upd reqs given a NULL parent
		run=N	Number of upd reqs granted CPU time
	Relinqs	n=N	Number of relinquish cookie requests seen
		nul=N	Number of rlq reqs given a NULL parent
		wcr=N	Number of rlq reqs waited on completion of creation
	AttrChg	n=N	Number of attribute changed requests seen
		ok=N	Number of attr changed requests queued
		nbf=N	Number of attr changed rejected -ENOBUFS
		oom=N	Number of attr changed failed -ENOMEM
		run=N	Number of attr changed ops given CPU time
	Allocs	n=N	Number of allocation requests seen
		ok=N	Number of successful alloc reqs
		wt=N	Number of alloc reqs that waited on lookup completion
		nbf=N	Number of alloc reqs rejected -ENOBUFS
		int=N	Number of alloc reqs aborted -ERESTARTSYS
		ops=N	Number of alloc reqs submitted
		owt=N	Number of alloc reqs waited for CPU time
		abt=N	Number of alloc reqs aborted due to object death
	Retrvls	n=N	Number of retrieval (read) requests seen
		ok=N	Number of successful retr reqs
		wt=N	Number of retr reqs that waited on lookup completion
		nod=N	Number of retr reqs returned -ENODATA
		nbf=N	Number of retr reqs rejected -ENOBUFS
		int=N	Number of retr reqs aborted -ERESTARTSYS
		oom=N	Number of retr reqs failed -ENOMEM
		ops=N	Number of retr reqs submitted
		owt=N	Number of retr reqs waited for CPU time
		abt=N	Number of retr reqs aborted due to object death
	Stores	n=N	Number of storage (write) requests seen
		ok=N	Number of successful store reqs
		agn=N	Number of store reqs on a page already pending storage
		nbf=N	Number of store reqs rejected -ENOBUFS
		oom=N	Number of store reqs failed -ENOMEM
		ops=N	Number of store reqs submitted
		run=N	Number of store reqs granted CPU time
		pgs=N	Number of pages given store req processing time
		rxd=N	Number of store reqs deleted from tracking tree
		olm=N	Number of store reqs over store limit
	VmScan	nos=N	Number of release reqs against pages with no pending store
		gon=N	Number of release reqs against pages stored by time lock granted
		bsy=N	Number of release reqs ignored due to in-progress store
		can=N	Number of page stores cancelled due to release req
	Ops	pend=N	Number of times async ops added to pending queues
		run=N	Number of times async ops given CPU time
		enq=N	Number of times async ops queued for processing
		can=N	Number of async ops cancelled
		rej=N	Number of async ops rejected due to object lookup/create failure
		dfr=N	Number of async ops queued for deferred release
		rel=N	Number of async ops released
		gc=N	Number of deferred-release async ops garbage collected
	CacheOp	alo=N	Number of in-progress alloc_object() cache ops
		luo=N	Number of in-progress lookup_object() cache ops
		luc=N	Number of in-progress lookup_complete() cache ops
		gro=N	Number of in-progress grab_object() cache ops
		upo=N	Number of in-progress update_object() cache ops
		dro=N	Number of in-progress drop_object() cache ops
		pto=N	Number of in-progress put_object() cache ops
		syn=N	Number of in-progress sync_cache() cache ops
		atc=N	Number of in-progress attr_changed() cache ops
		rap=N	Number of in-progress read_or_alloc_page() cache ops
		ras=N	Number of in-progress read_or_alloc_pages() cache ops
		alp=N	Number of in-progress allocate_page() cache ops
		als=N	Number of in-progress allocate_pages() cache ops
		wrp=N	Number of in-progress write_page() cache ops
		ucp=N	Number of in-progress uncache_page() cache ops
		dsp=N	Number of in-progress dissociate_pages() cache ops


 (*) /proc/fs/fscache/histogram

	cat /proc/fs/fscache/histogram
	JIFS  SECS  OBJ INST  OP RUNS   OBJ RUNS  RETRV DLY RETRIEVLS
	===== ===== ========= ========= ========= ========= =========

     This shows the breakdown of the number of times each amount of time
     between 0 jiffies and HZ-1 jiffies a variety of tasks took to run.  The
     columns are as follows:

	COLUMN		TIME MEASUREMENT
	=======		=======================================================
	OBJ INST	Length of time to instantiate an object
	OP RUNS		Length of time a call to process an operation took
	OBJ RUNS	Length of time a call to process an object event took
	RETRV DLY	Time between an requesting a read and lookup completing
	RETRIEVLS	Time between beginning and end of a retrieval

     Each row shows the number of events that took a particular range of times.
     Each step is 1 jiffy in size.  The JIFS column indicates the particular
     jiffy range covered, and the SECS field the equivalent number of seconds.


===========
OBJECT LIST
===========

If CONFIG_FSCACHE_OBJECT_LIST is enabled, the FS-Cache facility will maintain a
list of all the objects currently allocated and allow them to be viewed
through:

	/proc/fs/fscache/objects

This will look something like:

	[root@andromeda ~]# head /proc/fs/fscache/objects
	OBJECT   PARENT   STAT CHLDN OPS OOP IPR EX READS EM EV F S | NETFS_COOKIE_DEF TY FL NETFS_DATA       OBJECT_KEY, AUX_DATA
	======== ======== ==== ===== === === === == ===== == == = = | ================ == == ================ ================
	   17e4b        2 ACTV     0   0   0   0  0     0 7b  4 0 0 | NFS.fh           DT  0 ffff88001dd82820 010006017edcf8bbc93b43298fdfbe71e50b57b13a172c0117f38472, e567634700000000000000000000000063f2404a000000000000000000000000c9030000000000000000000063f2404a
	   1693a        2 ACTV     0   0   0   0  0     0 7b  4 0 0 | NFS.fh           DT  0 ffff88002db23380 010006017edcf8bbc93b43298fdfbe71e50b57b1e0162c01a2df0ea6, 420ebc4a000000000000000000000000420ebc4a0000000000000000000000000e1801000000000000000000420ebc4a

where the first set of columns before the '|' describe the object:

	COLUMN	DESCRIPTION
	=======	===============================================================
	OBJECT	Object debugging ID (appears as OBJ%x in some debug messages)
	PARENT	Debugging ID of parent object
	STAT	Object state
	CHLDN	Number of child objects of this object
	OPS	Number of outstanding operations on this object
	OOP	Number of outstanding child object management operations
	IPR
	EX	Number of outstanding exclusive operations
	READS	Number of outstanding read operations
	EM	Object's event mask
	EV	Events raised on this object
	F	Object flags
	S	Object work item busy state mask (1:pending 2:running)

and the second set of columns describe the object's cookie, if present:

	COLUMN		DESCRIPTION
	===============	=======================================================
	NETFS_COOKIE_DEF Name of netfs cookie definition
	TY		Cookie type (IX - index, DT - data, hex - special)
	FL		Cookie flags
	NETFS_DATA	Netfs private data stored in the cookie
	OBJECT_KEY	Object key	} 1 column, with separating comma
	AUX_DATA	Object aux data	} presence may be configured

The data shown may be filtered by attaching the a key to an appropriate keyring
before viewing the file.  Something like:

		keyctl add user fscache:objlist <restrictions> @s

where <restrictions> are a selection of the following letters:

	K	Show hexdump of object key (don't show if not given)
	A	Show hexdump of object aux data (don't show if not given)

and the following paired letters:

	C	Show objects that have a cookie
	c	Show objects that don't have a cookie
	B	Show objects that are busy
	b	Show objects that aren't busy
	W	Show objects that have pending writes
	w	Show objects that don't have pending writes
	R	Show objects that have outstanding reads
	r	Show objects that don't have outstanding reads
	S	Show objects that have work queued
	s	Show objects that don't have work queued

If neither side of a letter pair is given, then both are implied.  For example:

	keyctl add user fscache:objlist KB @s

shows objects that are busy, and lists their object keys, but does not dump
their auxiliary data.  It also implies "CcWwRrSs", but as 'B' is given, 'b' is
not implied.

By default all objects and all fields will be shown.


=========
DEBUGGING
=========

If CONFIG_FSCACHE_DEBUG is enabled, the FS-Cache facility can have runtime
debugging enabled by adjusting the value in:

	/sys/module/fscache/parameters/debug

This is a bitmask of debugging streams to enable:

	BIT	VALUE	STREAM				POINT
	=======	=======	===============================	=======================
	0	1	Cache management		Function entry trace
	1	2					Function exit trace
	2	4					General
	3	8	Cookie management		Function entry trace
	4	16					Function exit trace
	5	32					General
	6	64	Page handling			Function entry trace
	7	128					Function exit trace
	8	256					General
	9	512	Operation management		Function entry trace
	10	1024					Function exit trace
	11	2048					General

The appropriate set of values should be OR'd together and the result written to
the control file.  For example:

	echo $((1|8|64)) >/sys/module/fscache/parameters/debug

will turn on all function entry debugging.
Commit	Line	Data
2d6fff63 DH	1	==========================
	2	General Filesystem Caching
	3	==========================
	4
	5	========
	6	OVERVIEW
	7	========
	8
	9	This facility is a general purpose cache for network filesystems, though it
	10	could be used for caching other things such as ISO9660 filesystems too.
	11
	12	FS-Cache mediates between cache backends (such as CacheFS) and network
	13	filesystems:
	14
	15	+---------+
	16	\| \| +--------------+
	17	\| NFS \|--+ \| \|
	18	\| \| \| +-->\| CacheFS \|
	19	+---------+ \| +----------+ \| \| /dev/hda5 \|
	20	\| \| \| \| +--------------+
	21	+---------+ +-->\| \| \|
	22	\| \| \| \|--+
	23	\| AFS \|----->\| FS-Cache \|
	24	\| \| \| \|--+
	25	+---------+ +-->\| \| \|
	26	\| \| \| \| +--------------+
	27	+---------+ \| +----------+ \| \| \|
	28	\| \| \| +-->\| CacheFiles \|
	29	\| ISOFS \|--+ \| /var/cache \|
	30	\| \| +--------------+
	31	+---------+
	32
	33	Or to look at it another way, FS-Cache is a module that provides a caching
	34	facility to a network filesystem such that the cache is transparent to the
	35	user:
	36
	37	+---------+
	38	\| \|
	39	\| Server \|
	40	\| \|
	41	+---------+
	42	\| NETWORK
	43	~~~~~\|~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
	44	\|
	45	\| +----------+
	46	V \| \|
	47	+---------+ \| \|
	48	\| \| \| \|
	49	\| NFS \|----->\| FS-Cache \|
	50	\| \| \| \|--+
	51	+---------+ \| \| \| +--------------+ +--------------+
	52	\| \| \| \| \| \| \| \|
	53	V +----------+ +-->\| CacheFiles \|-->\| Ext3 \|
	54	+---------+ \| /var/cache \| \| /dev/sda6 \|
	55	\| \| +--------------+ +--------------+
	56	\| VFS \| ^ ^
	57	\| \| \| \|
	58	+---------+ +--------------+ \|
	59	\| KERNEL SPACE \| \|
	60	~~~~~\|~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\|~~~~~~\|~~~~
	61	\| USER SPACE \| \|
	62	V \| \|
	63	+---------+ +--------------+
	64	\| \| \| \|
65	\| Process \| \| cachefilesd \|
66	\| \| \| \|
67	+---------+ +--------------+
68
69
70	FS-Cache does not follow the idea of completely loading every netfs file
71	opened in its entirety into a cache before permitting it to be accessed and
72	then serving the pages out of that cache rather than the netfs inode because:
73
74	(1) It must be practical to operate without a cache.
75
76	(2) The size of any accessible file must not be limited to the size of the
77	cache.
78
79	(3) The combined size of all opened files (this includes mapped libraries)
80	must not be limited to the size of the cache.
81
82	(4) The user should not be forced to download an entire file just to do a
83	one-off access of a small portion of it (such as might be done with the
84	"file" program).
85
86	It instead serves the cache out in PAGE_SIZE chunks as and when requested by
87	the netfs('s) using it.
88
89
90	FS-Cache provides the following facilities:
91
92	(1) More than one cache can be used at once. Caches can be selected
93	explicitly by use of tags.
94
95	(2) Caches can be added / removed at any time.
96
97	(3) The netfs is provided with an interface that allows either party to
98	withdraw caching facilities from a file (required for (2)).
99
100	(4) The interface to the netfs returns as few errors as possible, preferring
101	rather to let the netfs remain oblivious.
102
103	(5) Cookies are used to represent indices, files and other objects to the
104	netfs. The simplest cookie is just a NULL pointer - indicating nothing
105	cached there.
106
107	(6) The netfs is allowed to propose - dynamically - any index hierarchy it
108	desires, though it must be aware that the index search function is
109	recursive, stack space is limited, and indices can only be children of
110	indices.
111
112	(7) Data I/O is done direct to and from the netfs's pages. The netfs
113	indicates that page A is at index B of the data-file represented by cookie
114	C, and that it should be read or written. The cache backend may or may
115	not start I/O on that page, but if it does, a netfs callback will be
116	invoked to indicate completion. The I/O may be either synchronous or
117	asynchronous.
118
119	(8) Cookies can be "retired" upon release. At this point FS-Cache will mark
120	them as obsolete and the index hierarchy rooted at that point will get
121	recycled.
122
123	(9) The netfs provides a "match" function for index searches. In addition to
124	saying whether a match was made or not, this can also specify that an
125	entry should be updated or deleted.
126
127	(10) As much as possible is done asynchronously.
128
129
130	FS-Cache maintains a virtual indexing tree in which all indices, files, objects
131	and pages are kept. Bits of this tree may actually reside in one or more
132	caches.
133
134	FSDEF
135	\|
136	+------------------------------------+
137	\| \|
138	NFS AFS
139	\| \|
140	+--------------------------+ +-----------+
141	\| \| \| \|
142	homedir mirror afs.org redhat.com
143	\| \| \|
144	+------------+ +---------------+ +----------+
145	\| \| \| \| \| \|
146	00001 00002 00007 00125 vol00001 vol00002
147	\| \| \| \| \|
148	+---+---+ +-----+ +---+ +------+------+ +-----+----+
149	\| \| \| \| \| \| \| \| \| \| \| \| \|
150	PG0 PG1 PG2 PG0 XATTR PG0 PG1 DIRENT DIRENT DIRENT R/W R/O Bak
151	\| \|
152	PG0 +-------+
153	\| \|
154	00001 00003
155	\|
156	+---+---+
157	\| \| \|
158	PG0 PG1 PG2
159
160	In the example above, you can see two netfs's being backed: NFS and AFS. These
161	have different index hierarchies:
162
163	(*) The NFS primary index contains per-server indices. Each server index is
164	indexed by NFS file handles to get data file objects. Each data file
165	objects can have an array of pages, but may also have further child
166	objects, such as extended attributes and directory entries. Extended
167	attribute objects themselves have page-array contents.
168
169	(*) The AFS primary index contains per-cell indices. Each cell index contains
170	per-logical-volume indices. Each of volume index contains up to three
171	indices for the read-write, read-only and backup mirrors of those volumes.
172	Each of these contains vnode data file objects, each of which contains an
173	array of pages.
174
175	The very top index is the FS-Cache master index in which individual netfs's
176	have entries.
177
178	Any index object may reside in more than one cache, provided it only has index
179	children. Any index with non-index object children will be assumed to only
180	reside in one cache.
181
182
183	The netfs API to FS-Cache can be found in:
184
185	Documentation/filesystems/caching/netfs-api.txt
186
187	The cache backend API to FS-Cache can be found in:
188
189	Documentation/filesystems/caching/backend-api.txt
190
36c95590 DH	191	A description of the internal representations and object state machine can be
	192	found in:
	193
	194	Documentation/filesystems/caching/object.txt
	195
2d6fff63 DH	196
	197	=======================
	198	STATISTICAL INFORMATION
	199	=======================
	200
	201	If FS-Cache is compiled with the following options enabled:
	202
2d6fff63 DH	203	CONFIG_FSCACHE_STATS=y
	204	CONFIG_FSCACHE_HISTOGRAM=y
	205
	206	then it will gather certain statistics and display them through a number of
	207	proc files.
	208
	209	(*) /proc/fs/fscache/stats
	210
	211	This shows counts of a number of events that can happen in FS-Cache:
	212
	213	CLASS EVENT MEANING
	214	======= ======= =======================================================
	215	Cookies idx=N Number of index cookies allocated
	216	dat=N Number of data storage cookies allocated
	217	spc=N Number of special cookies allocated
	218	Objects alc=N Number of objects allocated
	219	nal=N Number of object allocation failures
	220	avl=N Number of objects that reached the available state
	221	ded=N Number of objects that reached the dead state
	222	ChkAux non=N Number of objects that didn't have a coherency check
	223	ok=N Number of objects that passed a coherency check
	224	upd=N Number of objects that needed a coherency data update
	225	obs=N Number of objects that were declared obsolete
	226	Pages mrk=N Number of pages marked as being cached
	227	unc=N Number of uncache page requests seen
	228	Acquire n=N Number of acquire cookie requests seen
	229	nul=N Number of acq reqs given a NULL parent
	230	noc=N Number of acq reqs rejected due to no cache available
	231	ok=N Number of acq reqs succeeded
	232	nbf=N Number of acq reqs rejected due to error
	233	oom=N Number of acq reqs failed on ENOMEM
	234	Lookups n=N Number of lookup calls made on cache backends
	235	neg=N Number of negative lookups made
	236	pos=N Number of positive lookups made
	237	crt=N Number of objects created by lookup
fee096de	238	tmo=N Number of lookups timed out and requeued
2d6fff63 DH	239	Updates n=N Number of update cookie requests seen
	240	nul=N Number of upd reqs given a NULL parent
	241	run=N Number of upd reqs granted CPU time
	242	Relinqs n=N Number of relinquish cookie requests seen
	243	nul=N Number of rlq reqs given a NULL parent
	244	wcr=N Number of rlq reqs waited on completion of creation
	245	AttrChg n=N Number of attribute changed requests seen
	246	ok=N Number of attr changed requests queued
	247	nbf=N Number of attr changed rejected -ENOBUFS
	248	oom=N Number of attr changed failed -ENOMEM
	249	run=N Number of attr changed ops given CPU time
	250	Allocs n=N Number of allocation requests seen
	251	ok=N Number of successful alloc reqs
	252	wt=N Number of alloc reqs that waited on lookup completion
	253	nbf=N Number of alloc reqs rejected -ENOBUFS
5753c441	254	int=N Number of alloc reqs aborted -ERESTARTSYS
2d6fff63 DH	255	ops=N Number of alloc reqs submitted
2d6fff63 DH	256	owt=N Number of alloc reqs waited for CPU time
60d543ca	257	abt=N Number of alloc reqs aborted due to object death
2d6fff63 DH	258	Retrvls n=N Number of retrieval (read) requests seen
	259	ok=N Number of successful retr reqs
	260	wt=N Number of retr reqs that waited on lookup completion
	261	nod=N Number of retr reqs returned -ENODATA
	262	nbf=N Number of retr reqs rejected -ENOBUFS
	263	int=N Number of retr reqs aborted -ERESTARTSYS
	264	oom=N Number of retr reqs failed -ENOMEM
	265	ops=N Number of retr reqs submitted
	266	owt=N Number of retr reqs waited for CPU time
60d543ca	267	abt=N Number of retr reqs aborted due to object death
2d6fff63 DH	268	Stores n=N Number of storage (write) requests seen
	269	ok=N Number of successful store reqs
	270	agn=N Number of store reqs on a page already pending storage
	271	nbf=N Number of store reqs rejected -ENOBUFS
	272	oom=N Number of store reqs failed -ENOMEM
	273	ops=N Number of store reqs submitted
	274	run=N Number of store reqs granted CPU time
1bccf513 DH	275	pgs=N Number of pages given store req processing time
	276	rxd=N Number of store reqs deleted from tracking tree
	277	olm=N Number of store reqs over store limit
201a1542 DH	278	VmScan nos=N Number of release reqs against pages with no pending store
	279	gon=N Number of release reqs against pages stored by time lock granted
	280	bsy=N Number of release reqs ignored due to in-progress store
	281	can=N Number of page stores cancelled due to release req
2d6fff63 DH	282	Ops pend=N Number of times async ops added to pending queues
	283	run=N Number of times async ops given CPU time
	284	enq=N Number of times async ops queued for processing
5753c441	285	can=N Number of async ops cancelled
e3d4d28b	286	rej=N Number of async ops rejected due to object lookup/create failure
2d6fff63 DH	287	dfr=N Number of async ops queued for deferred release
	288	rel=N Number of async ops released
	289	gc=N Number of deferred-release async ops garbage collected
52bd75fd DH	290	CacheOp alo=N Number of in-progress alloc_object() cache ops
	291	luo=N Number of in-progress lookup_object() cache ops
	292	luc=N Number of in-progress lookup_complete() cache ops
	293	gro=N Number of in-progress grab_object() cache ops
	294	upo=N Number of in-progress update_object() cache ops
	295	dro=N Number of in-progress drop_object() cache ops
	296	pto=N Number of in-progress put_object() cache ops
	297	syn=N Number of in-progress sync_cache() cache ops
	298	atc=N Number of in-progress attr_changed() cache ops
	299	rap=N Number of in-progress read_or_alloc_page() cache ops
	300	ras=N Number of in-progress read_or_alloc_pages() cache ops
	301	alp=N Number of in-progress allocate_page() cache ops
	302	als=N Number of in-progress allocate_pages() cache ops
	303	wrp=N Number of in-progress write_page() cache ops
	304	ucp=N Number of in-progress uncache_page() cache ops
	305	dsp=N Number of in-progress dissociate_pages() cache ops
2d6fff63 DH	306
	307
	308	(*) /proc/fs/fscache/histogram
	309
	310	cat /proc/fs/fscache/histogram
7394daa8	311	JIFS SECS OBJ INST OP RUNS OBJ RUNS RETRV DLY RETRIEVLS
2d6fff63 DH	312	===== ===== ========= ========= ========= ========= =========
	313
	314	This shows the breakdown of the number of times each amount of time
	315	between 0 jiffies and HZ-1 jiffies a variety of tasks took to run. The
	316	columns are as follows:
	317
	318	COLUMN TIME MEASUREMENT
	319	======= =======================================================
	320	OBJ INST Length of time to instantiate an object
	321	OP RUNS Length of time a call to process an operation took
	322	OBJ RUNS Length of time a call to process an object event took
	323	RETRV DLY Time between an requesting a read and lookup completing
	324	RETRIEVLS Time between beginning and end of a retrieval
	325
	326	Each row shows the number of events that took a particular range of times.
7394daa8 DH	327	Each step is 1 jiffy in size. The JIFS column indicates the particular
7394daa8 DH	328	jiffy range covered, and the SECS field the equivalent number of seconds.
2d6fff63 DH	329
2d6fff63 DH	330
4fbf4291 DH	331	===========
	332	OBJECT LIST
	333	===========
	334
	335	If CONFIG_FSCACHE_OBJECT_LIST is enabled, the FS-Cache facility will maintain a
	336	list of all the objects currently allocated and allow them to be viewed
	337	through:
	338
	339	/proc/fs/fscache/objects
	340
	341	This will look something like:
	342
	343	[root@andromeda ~]# head /proc/fs/fscache/objects
	344	OBJECT PARENT STAT CHLDN OPS OOP IPR EX READS EM EV F S \| NETFS_COOKIE_DEF TY FL NETFS_DATA OBJECT_KEY, AUX_DATA
	345	======== ======== ==== ===== === === === == ===== == == = = \| ================ == == ================ ================
8b8edefa TH	346	17e4b 2 ACTV 0 0 0 0 0 0 7b 4 0 0 \| NFS.fh DT 0 ffff88001dd82820 010006017edcf8bbc93b43298fdfbe71e50b57b13a172c0117f38472, e567634700000000000000000000000063f2404a000000000000000000000000c9030000000000000000000063f2404a
8b8edefa TH	347	1693a 2 ACTV 0 0 0 0 0 0 7b 4 0 0 \| NFS.fh DT 0 ffff88002db23380 010006017edcf8bbc93b43298fdfbe71e50b57b1e0162c01a2df0ea6, 420ebc4a000000000000000000000000420ebc4a0000000000000000000000000e1801000000000000000000420ebc4a
4fbf4291 DH	348
	349	where the first set of columns before the '\|' describe the object:
	350
	351	COLUMN DESCRIPTION
	352	======= ===============================================================
	353	OBJECT Object debugging ID (appears as OBJ%x in some debug messages)
	354	PARENT Debugging ID of parent object
	355	STAT Object state
	356	CHLDN Number of child objects of this object
	357	OPS Number of outstanding operations on this object
	358	OOP Number of outstanding child object management operations
	359	IPR
	360	EX Number of outstanding exclusive operations
	361	READS Number of outstanding read operations
	362	EM Object's event mask
	363	EV Events raised on this object
	364	F Object flags
8b8edefa	365	S Object work item busy state mask (1:pending 2:running)
4fbf4291 DH	366
	367	and the second set of columns describe the object's cookie, if present:
	368
	369	COLUMN DESCRIPTION
	370	=============== =======================================================
	371	NETFS_COOKIE_DEF Name of netfs cookie definition
	372	TY Cookie type (IX - index, DT - data, hex - special)
	373	FL Cookie flags
	374	NETFS_DATA Netfs private data stored in the cookie
	375	OBJECT_KEY Object key } 1 column, with separating comma
	376	AUX_DATA Object aux data } presence may be configured
	377
	378	The data shown may be filtered by attaching the a key to an appropriate keyring
	379	before viewing the file. Something like:
	380
	381	keyctl add user fscache:objlist <restrictions> @s
	382
	383	where <restrictions> are a selection of the following letters:
	384
	385	K Show hexdump of object key (don't show if not given)
	386	A Show hexdump of object aux data (don't show if not given)
	387
	388	and the following paired letters:
	389
	390	C Show objects that have a cookie
	391	c Show objects that don't have a cookie
	392	B Show objects that are busy
	393	b Show objects that aren't busy
	394	W Show objects that have pending writes
	395	w Show objects that don't have pending writes
	396	R Show objects that have outstanding reads
	397	r Show objects that don't have outstanding reads
8b8edefa TH	398	S Show objects that have work queued
8b8edefa TH	399	s Show objects that don't have work queued
4fbf4291 DH	400
	401	If neither side of a letter pair is given, then both are implied. For example:
	402
	403	keyctl add user fscache:objlist KB @s
	404
	405	shows objects that are busy, and lists their object keys, but does not dump
	406	their auxiliary data. It also implies "CcWwRrSs", but as 'B' is given, 'b' is
	407	not implied.
	408
	409	By default all objects and all fields will be shown.
	410
	411
2d6fff63 DH	412	=========
	413	DEBUGGING
	414	=========
	415
7394daa8 DH	416	If CONFIG_FSCACHE_DEBUG is enabled, the FS-Cache facility can have runtime
7394daa8 DH	417	debugging enabled by adjusting the value in:
2d6fff63 DH	418
	419	/sys/module/fscache/parameters/debug
	420
	421	This is a bitmask of debugging streams to enable:
	422
	423	BIT VALUE STREAM POINT
	424	======= ======= =============================== =======================
	425	0 1 Cache management Function entry trace
	426	1 2 Function exit trace
	427	2 4 General
	428	3 8 Cookie management Function entry trace
	429	4 16 Function exit trace
	430	5 32 General
	431	6 64 Page handling Function entry trace
	432	7 128 Function exit trace
	433	8 256 General
	434	9 512 Operation management Function entry trace
	435	10 1024 Function exit trace
	436	11 2048 General
	437
	438	The appropriate set of values should be OR'd together and the result written to
	439	the control file. For example:
	440
	441	echo $((1\|8\|64)) >/sys/module/fscache/parameters/debug
	442
	443	will turn on all function entry debugging.