[net-next-2.6.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
	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
	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
	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 8 | NFS.fh           DT  0 ffff88001dd82820 010006017edcf8bbc93b43298fdfbe71e50b57b13a172c0117f38472, e567634700000000000000000000000063f2404a000000000000000000000000c9030000000000000000000063f2404a
	   1693a        2 ACTV     0   0   0   0  0     0 7b  4 0 8 | 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 slow-work work item flags

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 slow work queued
	s	Show objects that don't have slow 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
	238	Updates n=N Number of update cookie requests seen
	239	nul=N Number of upd reqs given a NULL parent
	240	run=N Number of upd reqs granted CPU time
	241	Relinqs n=N Number of relinquish cookie requests seen
	242	nul=N Number of rlq reqs given a NULL parent
	243	wcr=N Number of rlq reqs waited on completion of creation
	244	AttrChg n=N Number of attribute changed requests seen
	245	ok=N Number of attr changed requests queued
	246	nbf=N Number of attr changed rejected -ENOBUFS
	247	oom=N Number of attr changed failed -ENOMEM
	248	run=N Number of attr changed ops given CPU time
	249	Allocs n=N Number of allocation requests seen
	250	ok=N Number of successful alloc reqs
	251	wt=N Number of alloc reqs that waited on lookup completion
	252	nbf=N Number of alloc reqs rejected -ENOBUFS
5753c441	253	int=N Number of alloc reqs aborted -ERESTARTSYS
2d6fff63 DH	254	ops=N Number of alloc reqs submitted
	255	owt=N Number of alloc reqs waited for CPU time
	256	Retrvls n=N Number of retrieval (read) requests seen
	257	ok=N Number of successful retr reqs
	258	wt=N Number of retr reqs that waited on lookup completion
	259	nod=N Number of retr reqs returned -ENODATA
	260	nbf=N Number of retr reqs rejected -ENOBUFS
	261	int=N Number of retr reqs aborted -ERESTARTSYS
	262	oom=N Number of retr reqs failed -ENOMEM
	263	ops=N Number of retr reqs submitted
	264	owt=N Number of retr reqs waited for CPU time
	265	Stores n=N Number of storage (write) requests seen
	266	ok=N Number of successful store reqs
	267	agn=N Number of store reqs on a page already pending storage
	268	nbf=N Number of store reqs rejected -ENOBUFS
	269	oom=N Number of store reqs failed -ENOMEM
	270	ops=N Number of store reqs submitted
	271	run=N Number of store reqs granted CPU time
1bccf513 DH	272	pgs=N Number of pages given store req processing time
	273	rxd=N Number of store reqs deleted from tracking tree
	274	olm=N Number of store reqs over store limit
201a1542 DH	275	VmScan nos=N Number of release reqs against pages with no pending store
	276	gon=N Number of release reqs against pages stored by time lock granted
	277	bsy=N Number of release reqs ignored due to in-progress store
	278	can=N Number of page stores cancelled due to release req
2d6fff63 DH	279	Ops pend=N Number of times async ops added to pending queues
	280	run=N Number of times async ops given CPU time
	281	enq=N Number of times async ops queued for processing
5753c441	282	can=N Number of async ops cancelled
e3d4d28b	283	rej=N Number of async ops rejected due to object lookup/create failure
2d6fff63 DH	284	dfr=N Number of async ops queued for deferred release
	285	rel=N Number of async ops released
	286	gc=N Number of deferred-release async ops garbage collected
52bd75fd DH	287	CacheOp alo=N Number of in-progress alloc_object() cache ops
	288	luo=N Number of in-progress lookup_object() cache ops
	289	luc=N Number of in-progress lookup_complete() cache ops
	290	gro=N Number of in-progress grab_object() cache ops
	291	upo=N Number of in-progress update_object() cache ops
	292	dro=N Number of in-progress drop_object() cache ops
	293	pto=N Number of in-progress put_object() cache ops
	294	syn=N Number of in-progress sync_cache() cache ops
	295	atc=N Number of in-progress attr_changed() cache ops
	296	rap=N Number of in-progress read_or_alloc_page() cache ops
	297	ras=N Number of in-progress read_or_alloc_pages() cache ops
	298	alp=N Number of in-progress allocate_page() cache ops
	299	als=N Number of in-progress allocate_pages() cache ops
	300	wrp=N Number of in-progress write_page() cache ops
	301	ucp=N Number of in-progress uncache_page() cache ops
	302	dsp=N Number of in-progress dissociate_pages() cache ops
2d6fff63 DH	303
	304
	305	(*) /proc/fs/fscache/histogram
	306
	307	cat /proc/fs/fscache/histogram
7394daa8	308	JIFS SECS OBJ INST OP RUNS OBJ RUNS RETRV DLY RETRIEVLS
2d6fff63 DH	309	===== ===== ========= ========= ========= ========= =========
	310
	311	This shows the breakdown of the number of times each amount of time
	312	between 0 jiffies and HZ-1 jiffies a variety of tasks took to run. The
	313	columns are as follows:
	314
	315	COLUMN TIME MEASUREMENT
	316	======= =======================================================
	317	OBJ INST Length of time to instantiate an object
	318	OP RUNS Length of time a call to process an operation took
	319	OBJ RUNS Length of time a call to process an object event took
	320	RETRV DLY Time between an requesting a read and lookup completing
	321	RETRIEVLS Time between beginning and end of a retrieval
	322
	323	Each row shows the number of events that took a particular range of times.
7394daa8 DH	324	Each step is 1 jiffy in size. The JIFS column indicates the particular
7394daa8 DH	325	jiffy range covered, and the SECS field the equivalent number of seconds.
2d6fff63 DH	326
2d6fff63 DH	327
4fbf4291 DH	328	===========
	329	OBJECT LIST
	330	===========
	331
	332	If CONFIG_FSCACHE_OBJECT_LIST is enabled, the FS-Cache facility will maintain a
	333	list of all the objects currently allocated and allow them to be viewed
	334	through:
	335
	336	/proc/fs/fscache/objects
	337
	338	This will look something like:
	339
	340	[root@andromeda ~]# head /proc/fs/fscache/objects
	341	OBJECT PARENT STAT CHLDN OPS OOP IPR EX READS EM EV F S \| NETFS_COOKIE_DEF TY FL NETFS_DATA OBJECT_KEY, AUX_DATA
	342	======== ======== ==== ===== === === === == ===== == == = = \| ================ == == ================ ================
	343	17e4b 2 ACTV 0 0 0 0 0 0 7b 4 0 8 \| NFS.fh DT 0 ffff88001dd82820 010006017edcf8bbc93b43298fdfbe71e50b57b13a172c0117f38472, e567634700000000000000000000000063f2404a000000000000000000000000c9030000000000000000000063f2404a
	344	1693a 2 ACTV 0 0 0 0 0 0 7b 4 0 8 \| NFS.fh DT 0 ffff88002db23380 010006017edcf8bbc93b43298fdfbe71e50b57b1e0162c01a2df0ea6, 420ebc4a000000000000000000000000420ebc4a0000000000000000000000000e1801000000000000000000420ebc4a
	345
	346	where the first set of columns before the '\|' describe the object:
	347
	348	COLUMN DESCRIPTION
	349	======= ===============================================================
	350	OBJECT Object debugging ID (appears as OBJ%x in some debug messages)
	351	PARENT Debugging ID of parent object
	352	STAT Object state
	353	CHLDN Number of child objects of this object
	354	OPS Number of outstanding operations on this object
	355	OOP Number of outstanding child object management operations
	356	IPR
	357	EX Number of outstanding exclusive operations
	358	READS Number of outstanding read operations
	359	EM Object's event mask
	360	EV Events raised on this object
	361	F Object flags
	362	S Object slow-work work item flags
	363
	364	and the second set of columns describe the object's cookie, if present:
	365
	366	COLUMN DESCRIPTION
	367	=============== =======================================================
	368	NETFS_COOKIE_DEF Name of netfs cookie definition
	369	TY Cookie type (IX - index, DT - data, hex - special)
	370	FL Cookie flags
	371	NETFS_DATA Netfs private data stored in the cookie
	372	OBJECT_KEY Object key } 1 column, with separating comma
	373	AUX_DATA Object aux data } presence may be configured
	374
	375	The data shown may be filtered by attaching the a key to an appropriate keyring
	376	before viewing the file. Something like:
	377
	378	keyctl add user fscache:objlist <restrictions> @s
	379
	380	where <restrictions> are a selection of the following letters:
	381
	382	K Show hexdump of object key (don't show if not given)
	383	A Show hexdump of object aux data (don't show if not given)
	384
	385	and the following paired letters:
	386
	387	C Show objects that have a cookie
	388	c Show objects that don't have a cookie
	389	B Show objects that are busy
	390	b Show objects that aren't busy
	391	W Show objects that have pending writes
392	w Show objects that don't have pending writes
393	R Show objects that have outstanding reads
394	r Show objects that don't have outstanding reads
395	S Show objects that have slow work queued
396	s Show objects that don't have slow work queued
397
398	If neither side of a letter pair is given, then both are implied. For example:
399
400	keyctl add user fscache:objlist KB @s
401
402	shows objects that are busy, and lists their object keys, but does not dump
403	their auxiliary data. It also implies "CcWwRrSs", but as 'B' is given, 'b' is
404	not implied.
405
406	By default all objects and all fields will be shown.
407
408
2d6fff63 DH	409	=========
	410	DEBUGGING
	411	=========
	412
7394daa8 DH	413	If CONFIG_FSCACHE_DEBUG is enabled, the FS-Cache facility can have runtime
7394daa8 DH	414	debugging enabled by adjusting the value in:
2d6fff63 DH	415
	416	/sys/module/fscache/parameters/debug
	417
	418	This is a bitmask of debugging streams to enable:
	419
	420	BIT VALUE STREAM POINT
	421	======= ======= =============================== =======================
	422	0 1 Cache management Function entry trace
	423	1 2 Function exit trace
	424	2 4 General
	425	3 8 Cookie management Function entry trace
	426	4 16 Function exit trace
	427	5 32 General
	428	6 64 Page handling Function entry trace
	429	7 128 Function exit trace
	430	8 256 General
	431	9 512 Operation management Function entry trace
	432	10 1024 Function exit trace
	433	11 2048 General
	434
	435	The appropriate set of values should be OR'd together and the result written to
	436	the control file. For example:
	437
	438	echo $((1\|8\|64)) >/sys/module/fscache/parameters/debug
	439
	440	will turn on all function entry debugging.