566 строки
30 KiB
ReStructuredText
566 строки
30 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
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==========================
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General Filesystem Caching
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==========================
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Overview
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========
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This facility is a general purpose cache for network filesystems, though it
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could be used for caching other things such as ISO9660 filesystems too.
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FS-Cache mediates between cache backends (such as CacheFS) and network
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filesystems::
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+---------+
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| | +--------------+
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| NFS |--+ | |
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| | | +-->| CacheFS |
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+---------+ | +----------+ | | /dev/hda5 |
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| | | | +--------------+
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+---------+ +-->| | |
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| | | |--+
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| AFS |----->| FS-Cache |
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| | | |--+
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+---------+ +-->| | |
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| | | | +--------------+
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+---------+ | +----------+ | | |
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| | | +-->| CacheFiles |
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| ISOFS |--+ | /var/cache |
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| | +--------------+
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+---------+
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Or to look at it another way, FS-Cache is a module that provides a caching
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facility to a network filesystem such that the cache is transparent to the
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user::
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+---------+
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| Server |
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+---------+
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| NETWORK
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~~~~~|~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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| +----------+
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V | |
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+---------+ | |
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| | | |
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| NFS |----->| FS-Cache |
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| | | |--+
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+---------+ | | | +--------------+ +--------------+
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| | | | | | | |
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V +----------+ +-->| CacheFiles |-->| Ext3 |
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+---------+ | /var/cache | | /dev/sda6 |
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| | +--------------+ +--------------+
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| VFS | ^ ^
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| | | |
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+---------+ +--------------+ |
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| KERNEL SPACE | |
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~~~~~|~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~|~~~~~~|~~~~
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| USER SPACE | |
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V | |
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+---------+ +--------------+
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| Process | | cachefilesd |
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+---------+ +--------------+
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FS-Cache does not follow the idea of completely loading every netfs file
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opened in its entirety into a cache before permitting it to be accessed and
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then serving the pages out of that cache rather than the netfs inode because:
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(1) It must be practical to operate without a cache.
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(2) The size of any accessible file must not be limited to the size of the
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cache.
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(3) The combined size of all opened files (this includes mapped libraries)
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must not be limited to the size of the cache.
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(4) The user should not be forced to download an entire file just to do a
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one-off access of a small portion of it (such as might be done with the
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"file" program).
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It instead serves the cache out in PAGE_SIZE chunks as and when requested by
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the netfs('s) using it.
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FS-Cache provides the following facilities:
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(1) More than one cache can be used at once. Caches can be selected
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explicitly by use of tags.
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(2) Caches can be added / removed at any time.
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(3) The netfs is provided with an interface that allows either party to
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withdraw caching facilities from a file (required for (2)).
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(4) The interface to the netfs returns as few errors as possible, preferring
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rather to let the netfs remain oblivious.
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(5) Cookies are used to represent indices, files and other objects to the
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netfs. The simplest cookie is just a NULL pointer - indicating nothing
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cached there.
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(6) The netfs is allowed to propose - dynamically - any index hierarchy it
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desires, though it must be aware that the index search function is
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recursive, stack space is limited, and indices can only be children of
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indices.
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(7) Data I/O is done direct to and from the netfs's pages. The netfs
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indicates that page A is at index B of the data-file represented by cookie
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C, and that it should be read or written. The cache backend may or may
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not start I/O on that page, but if it does, a netfs callback will be
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invoked to indicate completion. The I/O may be either synchronous or
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asynchronous.
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(8) Cookies can be "retired" upon release. At this point FS-Cache will mark
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them as obsolete and the index hierarchy rooted at that point will get
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recycled.
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(9) The netfs provides a "match" function for index searches. In addition to
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saying whether a match was made or not, this can also specify that an
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entry should be updated or deleted.
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(10) As much as possible is done asynchronously.
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FS-Cache maintains a virtual indexing tree in which all indices, files, objects
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and pages are kept. Bits of this tree may actually reside in one or more
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caches::
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FSDEF
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+------------------------------------+
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NFS AFS
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+--------------------------+ +-----------+
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homedir mirror afs.org redhat.com
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+------------+ +---------------+ +----------+
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00001 00002 00007 00125 vol00001 vol00002
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+---+---+ +-----+ +---+ +------+------+ +-----+----+
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PG0 PG1 PG2 PG0 XATTR PG0 PG1 DIRENT DIRENT DIRENT R/W R/O Bak
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PG0 +-------+
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00001 00003
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+---+---+
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PG0 PG1 PG2
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In the example above, you can see two netfs's being backed: NFS and AFS. These
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have different index hierarchies:
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* The NFS primary index contains per-server indices. Each server index is
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indexed by NFS file handles to get data file objects. Each data file
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objects can have an array of pages, but may also have further child
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objects, such as extended attributes and directory entries. Extended
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attribute objects themselves have page-array contents.
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* The AFS primary index contains per-cell indices. Each cell index contains
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per-logical-volume indices. Each of volume index contains up to three
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indices for the read-write, read-only and backup mirrors of those volumes.
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Each of these contains vnode data file objects, each of which contains an
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array of pages.
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The very top index is the FS-Cache master index in which individual netfs's
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have entries.
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Any index object may reside in more than one cache, provided it only has index
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children. Any index with non-index object children will be assumed to only
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reside in one cache.
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The netfs API to FS-Cache can be found in:
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Documentation/filesystems/caching/netfs-api.rst
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The cache backend API to FS-Cache can be found in:
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Documentation/filesystems/caching/backend-api.rst
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A description of the internal representations and object state machine can be
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found in:
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Documentation/filesystems/caching/object.rst
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Statistical Information
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=======================
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If FS-Cache is compiled with the following options enabled::
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CONFIG_FSCACHE_STATS=y
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CONFIG_FSCACHE_HISTOGRAM=y
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then it will gather certain statistics and display them through a number of
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proc files.
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/proc/fs/fscache/stats
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----------------------
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This shows counts of a number of events that can happen in FS-Cache:
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+--------------+-------+-------------------------------------------------------+
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|CLASS |EVENT |MEANING |
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+==============+=======+=======================================================+
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|Cookies |idx=N |Number of index cookies allocated |
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+ +-------+-------------------------------------------------------+
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| |dat=N |Number of data storage cookies allocated |
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+ +-------+-------------------------------------------------------+
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| |spc=N |Number of special cookies allocated |
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+--------------+-------+-------------------------------------------------------+
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|Objects |alc=N |Number of objects allocated |
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+ +-------+-------------------------------------------------------+
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| |nal=N |Number of object allocation failures |
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+ +-------+-------------------------------------------------------+
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| |avl=N |Number of objects that reached the available state |
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+ +-------+-------------------------------------------------------+
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| |ded=N |Number of objects that reached the dead state |
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+--------------+-------+-------------------------------------------------------+
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|ChkAux |non=N |Number of objects that didn't have a coherency check |
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+ +-------+-------------------------------------------------------+
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| |ok=N |Number of objects that passed a coherency check |
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+ +-------+-------------------------------------------------------+
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| |upd=N |Number of objects that needed a coherency data update |
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+ +-------+-------------------------------------------------------+
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| |obs=N |Number of objects that were declared obsolete |
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+--------------+-------+-------------------------------------------------------+
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|Pages |mrk=N |Number of pages marked as being cached |
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| |unc=N |Number of uncache page requests seen |
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+--------------+-------+-------------------------------------------------------+
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|Acquire |n=N |Number of acquire cookie requests seen |
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+ +-------+-------------------------------------------------------+
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| |nul=N |Number of acq reqs given a NULL parent |
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+ +-------+-------------------------------------------------------+
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| |noc=N |Number of acq reqs rejected due to no cache available |
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+ +-------+-------------------------------------------------------+
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| |ok=N |Number of acq reqs succeeded |
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+ +-------+-------------------------------------------------------+
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| |nbf=N |Number of acq reqs rejected due to error |
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+ +-------+-------------------------------------------------------+
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| |oom=N |Number of acq reqs failed on ENOMEM |
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+--------------+-------+-------------------------------------------------------+
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|Lookups |n=N |Number of lookup calls made on cache backends |
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+ +-------+-------------------------------------------------------+
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| |neg=N |Number of negative lookups made |
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+ +-------+-------------------------------------------------------+
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| |pos=N |Number of positive lookups made |
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+ +-------+-------------------------------------------------------+
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| |crt=N |Number of objects created by lookup |
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+ +-------+-------------------------------------------------------+
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| |tmo=N |Number of lookups timed out and requeued |
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+--------------+-------+-------------------------------------------------------+
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|Updates |n=N |Number of update cookie requests seen |
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+ +-------+-------------------------------------------------------+
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| |nul=N |Number of upd reqs given a NULL parent |
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+ +-------+-------------------------------------------------------+
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| |run=N |Number of upd reqs granted CPU time |
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+--------------+-------+-------------------------------------------------------+
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|Relinqs |n=N |Number of relinquish cookie requests seen |
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+ +-------+-------------------------------------------------------+
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| |nul=N |Number of rlq reqs given a NULL parent |
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+ +-------+-------------------------------------------------------+
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| |wcr=N |Number of rlq reqs waited on completion of creation |
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+--------------+-------+-------------------------------------------------------+
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|AttrChg |n=N |Number of attribute changed requests seen |
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+ +-------+-------------------------------------------------------+
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| |ok=N |Number of attr changed requests queued |
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+ +-------+-------------------------------------------------------+
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| |nbf=N |Number of attr changed rejected -ENOBUFS |
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+ +-------+-------------------------------------------------------+
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| |oom=N |Number of attr changed failed -ENOMEM |
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+ +-------+-------------------------------------------------------+
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| |run=N |Number of attr changed ops given CPU time |
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+--------------+-------+-------------------------------------------------------+
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|Allocs |n=N |Number of allocation requests seen |
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+ +-------+-------------------------------------------------------+
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| |ok=N |Number of successful alloc reqs |
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+ +-------+-------------------------------------------------------+
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| |wt=N |Number of alloc reqs that waited on lookup completion |
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+ +-------+-------------------------------------------------------+
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| |nbf=N |Number of alloc reqs rejected -ENOBUFS |
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+ +-------+-------------------------------------------------------+
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| |int=N |Number of alloc reqs aborted -ERESTARTSYS |
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+ +-------+-------------------------------------------------------+
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| |ops=N |Number of alloc reqs submitted |
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+ +-------+-------------------------------------------------------+
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| |owt=N |Number of alloc reqs waited for CPU time |
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+ +-------+-------------------------------------------------------+
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| |abt=N |Number of alloc reqs aborted due to object death |
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+--------------+-------+-------------------------------------------------------+
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|Retrvls |n=N |Number of retrieval (read) requests seen |
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+ +-------+-------------------------------------------------------+
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| |ok=N |Number of successful retr reqs |
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+ +-------+-------------------------------------------------------+
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| |wt=N |Number of retr reqs that waited on lookup completion |
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+ +-------+-------------------------------------------------------+
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| |nod=N |Number of retr reqs returned -ENODATA |
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+ +-------+-------------------------------------------------------+
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| |nbf=N |Number of retr reqs rejected -ENOBUFS |
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+ +-------+-------------------------------------------------------+
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| |int=N |Number of retr reqs aborted -ERESTARTSYS |
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+ +-------+-------------------------------------------------------+
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| |oom=N |Number of retr reqs failed -ENOMEM |
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+ +-------+-------------------------------------------------------+
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| |ops=N |Number of retr reqs submitted |
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+ +-------+-------------------------------------------------------+
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| |owt=N |Number of retr reqs waited for CPU time |
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+ +-------+-------------------------------------------------------+
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| |abt=N |Number of retr reqs aborted due to object death |
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+--------------+-------+-------------------------------------------------------+
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|Stores |n=N |Number of storage (write) requests seen |
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+ +-------+-------------------------------------------------------+
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| |ok=N |Number of successful store reqs |
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+ +-------+-------------------------------------------------------+
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| |agn=N |Number of store reqs on a page already pending storage |
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+ +-------+-------------------------------------------------------+
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| |nbf=N |Number of store reqs rejected -ENOBUFS |
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+ +-------+-------------------------------------------------------+
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| |oom=N |Number of store reqs failed -ENOMEM |
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+ +-------+-------------------------------------------------------+
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| |ops=N |Number of store reqs submitted |
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+ +-------+-------------------------------------------------------+
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| |run=N |Number of store reqs granted CPU time |
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+ +-------+-------------------------------------------------------+
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| |pgs=N |Number of pages given store req processing time |
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+ +-------+-------------------------------------------------------+
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| |rxd=N |Number of store reqs deleted from tracking tree |
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+ +-------+-------------------------------------------------------+
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| |olm=N |Number of store reqs over store limit |
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+--------------+-------+-------------------------------------------------------+
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|VmScan |nos=N |Number of release reqs against pages with no |
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| | |pending store |
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+ +-------+-------------------------------------------------------+
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| |gon=N |Number of release reqs against pages stored by |
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| | |time lock granted |
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+ +-------+-------------------------------------------------------+
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| |bsy=N |Number of release reqs ignored due to in-progress store|
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+ +-------+-------------------------------------------------------+
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| |can=N |Number of page stores cancelled due to release req |
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+--------------+-------+-------------------------------------------------------+
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|Ops |pend=N |Number of times async ops added to pending queues |
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+ +-------+-------------------------------------------------------+
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| |run=N |Number of times async ops given CPU time |
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+ +-------+-------------------------------------------------------+
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| |enq=N |Number of times async ops queued for processing |
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+ +-------+-------------------------------------------------------+
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| |can=N |Number of async ops cancelled |
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+ +-------+-------------------------------------------------------+
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| |rej=N |Number of async ops rejected due to object |
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| | |lookup/create failure |
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+ +-------+-------------------------------------------------------+
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| |ini=N |Number of async ops initialised |
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+ +-------+-------------------------------------------------------+
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| |dfr=N |Number of async ops queued for deferred release |
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+ +-------+-------------------------------------------------------+
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| |rel=N |Number of async ops released |
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| | |(should equal ini=N when idle) |
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+ +-------+-------------------------------------------------------+
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| |gc=N |Number of deferred-release async ops garbage collected |
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+--------------+-------+-------------------------------------------------------+
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|CacheOp |alo=N |Number of in-progress alloc_object() cache ops |
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+ +-------+-------------------------------------------------------+
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| |luo=N |Number of in-progress lookup_object() cache ops |
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+ +-------+-------------------------------------------------------+
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| |luc=N |Number of in-progress lookup_complete() cache ops |
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+ +-------+-------------------------------------------------------+
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| |gro=N |Number of in-progress grab_object() cache ops |
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+ +-------+-------------------------------------------------------+
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| |upo=N |Number of in-progress update_object() cache ops |
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+ +-------+-------------------------------------------------------+
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| |dro=N |Number of in-progress drop_object() cache ops |
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+ +-------+-------------------------------------------------------+
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| |pto=N |Number of in-progress put_object() cache ops |
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+ +-------+-------------------------------------------------------+
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| |syn=N |Number of in-progress sync_cache() cache ops |
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+ +-------+-------------------------------------------------------+
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| |atc=N |Number of in-progress attr_changed() cache ops |
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+ +-------+-------------------------------------------------------+
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| |rap=N |Number of in-progress read_or_alloc_page() cache ops |
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+ +-------+-------------------------------------------------------+
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| |ras=N |Number of in-progress read_or_alloc_pages() cache ops |
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+ +-------+-------------------------------------------------------+
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| |alp=N |Number of in-progress allocate_page() cache ops |
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+ +-------+-------------------------------------------------------+
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| |als=N |Number of in-progress allocate_pages() cache ops |
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+ +-------+-------------------------------------------------------+
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| |wrp=N |Number of in-progress write_page() cache ops |
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+ +-------+-------------------------------------------------------+
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| |ucp=N |Number of in-progress uncache_page() cache ops |
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+ +-------+-------------------------------------------------------+
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| |dsp=N |Number of in-progress dissociate_pages() cache ops |
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+--------------+-------+-------------------------------------------------------+
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|CacheEv |nsp=N |Number of object lookups/creations rejected due to |
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| | |lack of space |
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+ +-------+-------------------------------------------------------+
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| |stl=N |Number of stale objects deleted |
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+ +-------+-------------------------------------------------------+
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| |rtr=N |Number of objects retired when relinquished |
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+ +-------+-------------------------------------------------------+
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| |cul=N |Number of objects culled |
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+--------------+-------+-------------------------------------------------------+
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/proc/fs/fscache/histogram
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--------------------------
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::
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cat /proc/fs/fscache/histogram
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JIFS SECS OBJ INST OP RUNS OBJ RUNS RETRV DLY RETRIEVLS
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===== ===== ========= ========= ========= ========= =========
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This shows the breakdown of the number of times each amount of time
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between 0 jiffies and HZ-1 jiffies a variety of tasks took to run. The
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columns are as follows:
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========= =======================================================
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COLUMN TIME MEASUREMENT
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========= =======================================================
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OBJ INST Length of time to instantiate an object
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OP RUNS Length of time a call to process an operation took
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OBJ RUNS Length of time a call to process an object event took
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RETRV DLY Time between an requesting a read and lookup completing
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RETRIEVLS Time between beginning and end of a retrieval
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========= =======================================================
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Each row shows the number of events that took a particular range of times.
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Each step is 1 jiffy in size. The JIFS column indicates the particular
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jiffy range covered, and the SECS field the equivalent number of seconds.
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Object List
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===========
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If CONFIG_FSCACHE_OBJECT_LIST is enabled, the FS-Cache facility will maintain a
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list of all the objects currently allocated and allow them to be viewed
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through::
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/proc/fs/fscache/objects
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This will look something like::
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[root@andromeda ~]# head /proc/fs/fscache/objects
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OBJECT PARENT STAT CHLDN OPS OOP IPR EX READS EM EV F S | NETFS_COOKIE_DEF TY FL NETFS_DATA OBJECT_KEY, AUX_DATA
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======== ======== ==== ===== === === === == ===== == == = = | ================ == == ================ ================
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17e4b 2 ACTV 0 0 0 0 0 0 7b 4 0 0 | NFS.fh DT 0 ffff88001dd82820 010006017edcf8bbc93b43298fdfbe71e50b57b13a172c0117f38472, e567634700000000000000000000000063f2404a000000000000000000000000c9030000000000000000000063f2404a
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1693a 2 ACTV 0 0 0 0 0 0 7b 4 0 0 | NFS.fh DT 0 ffff88002db23380 010006017edcf8bbc93b43298fdfbe71e50b57b1e0162c01a2df0ea6, 420ebc4a000000000000000000000000420ebc4a0000000000000000000000000e1801000000000000000000420ebc4a
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where the first set of columns before the '|' describe the object:
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======= ===============================================================
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COLUMN DESCRIPTION
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======= ===============================================================
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OBJECT Object debugging ID (appears as OBJ%x in some debug messages)
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PARENT Debugging ID of parent object
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STAT Object state
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CHLDN Number of child objects of this object
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OPS Number of outstanding operations on this object
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OOP Number of outstanding child object management operations
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IPR
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EX Number of outstanding exclusive operations
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READS Number of outstanding read operations
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EM Object's event mask
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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.
|