nfs: move more to Documentation/filesystems/nfs

Oops: I missed two files in the first commit that created this
directory.

Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>

3 files changed, 365 insertions, 0 deletions

diff --git a/Documentation/filesystems/nfs/00-INDEX b/Documentation/filesystems/nfs/00-INDEX
index 6ff3d212027b..2f68cd688769 100644
--- a/Documentation/filesystems/nfs/00-INDEX
+++ b/Documentation/filesystems/nfs/00-INDEX
@@ -2,6 +2,8 @@
         - this file (nfs-related documentation).
 Exporting
         - explanation of how to make filesystems exportable.
+knfsd-stats.txt
+        - statistics which the NFS server makes available to user space.
 nfs.txt
         - nfs client, and DNS resolution for fs_locations.
 nfs41-server.txt
@@ -10,3 +12,5 @@ nfs-rdma.txt
         - how to install and setup the Linux NFS/RDMA client and server software
 nfsroot.txt
         - short guide on setting up a diskless box with NFS root filesystem.
+rpc-cache.txt
+        - introduction to the caching mechanisms in the sunrpc layer.
diff --git a/Documentation/filesystems/nfs/knfsd-stats.txt b/Documentation/filesystems/nfs/knfsd-stats.txt
new file mode 100644
index 000000000000..64ced5149d37
--- /dev/null
+++ b/Documentation/filesystems/nfs/knfsd-stats.txt
@@ -0,0 +1,159 @@
+
+Kernel NFS Server Statistics
+============================
+
+This document describes the format and semantics of the statistics
+which the kernel NFS server makes available to userspace.  These
+statistics are available in several text form pseudo files, each of
+which is described separately below.
+
+In most cases you don't need to know these formats, as the nfsstat(8)
+program from the nfs-utils distribution provides a helpful command-line
+interface for extracting and printing them.
+
+All the files described here are formatted as a sequence of text lines,
+separated by newline '\n' characters.  Lines beginning with a hash
+'#' character are comments intended for humans and should be ignored
+by parsing routines.  All other lines contain a sequence of fields
+separated by whitespace.
+
+/proc/fs/nfsd/pool_stats
+------------------------
+
+This file is available in kernels from 2.6.30 onwards, if the
+/proc/fs/nfsd filesystem is mounted (it almost always should be).
+
+The first line is a comment which describes the fields present in
+all the other lines.  The other lines present the following data as
+a sequence of unsigned decimal numeric fields.  One line is shown
+for each NFS thread pool.
+
+All counters are 64 bits wide and wrap naturally.  There is no way
+to zero these counters, instead applications should do their own
+rate conversion.
+
+pool
+        The id number of the NFS thread pool to which this line applies.
+        This number does not change.
+
+        Thread pool ids are a contiguous set of small integers starting
+        at zero.  The maximum value depends on the thread pool mode, but
+        currently cannot be larger than the number of CPUs in the system.
+        Note that in the default case there will be a single thread pool
+        which contains all the nfsd threads and all the CPUs in the system,
+        and thus this file will have a single line with a pool id of "0".
+
+packets-arrived
+        Counts how many NFS packets have arrived.  More precisely, this
+        is the number of times that the network stack has notified the
+        sunrpc server layer that new data may be available on a transport
+        (e.g. an NFS or UDP socket or an NFS/RDMA endpoint).
+
+        Depending on the NFS workload patterns and various network stack
+        effects (such as Large Receive Offload) which can combine packets
+        on the wire, this may be either more or less than the number
+        of NFS calls received (which statistic is available elsewhere).
+        However this is a more accurate and less workload-dependent measure
+        of how much CPU load is being placed on the sunrpc server layer
+        due to NFS network traffic.
+
+sockets-enqueued
+        Counts how many times an NFS transport is enqueued to wait for
+        an nfsd thread to service it, i.e. no nfsd thread was considered
+        available.
+
+        The circumstance this statistic tracks indicates that there was NFS
+        network-facing work to be done but it couldn't be done immediately,
+        thus introducing a small delay in servicing NFS calls.  The ideal
+        rate of change for this counter is zero; significantly non-zero
+        values may indicate a performance limitation.
+
+        This can happen either because there are too few nfsd threads in the
+        thread pool for the NFS workload (the workload is thread-limited),
+        or because the NFS workload needs more CPU time than is available in
+        the thread pool (the workload is CPU-limited).  In the former case,
+        configuring more nfsd threads will probably improve the performance
+        of the NFS workload.  In the latter case, the sunrpc server layer is
+        already choosing not to wake idle nfsd threads because there are too
+        many nfsd threads which want to run but cannot, so configuring more
+        nfsd threads will make no difference whatsoever.  The overloads-avoided
+        statistic (see below) can be used to distinguish these cases.
+
+threads-woken
+        Counts how many times an idle nfsd thread is woken to try to
+        receive some data from an NFS transport.
+
+        This statistic tracks the circumstance where incoming
+        network-facing NFS work is being handled quickly, which is a good
+        thing.  The ideal rate of change for this counter will be close
+        to but less than the rate of change of the packets-arrived counter.
+
+overloads-avoided
+        Counts how many times the sunrpc server layer chose not to wake an
+        nfsd thread, despite the presence of idle nfsd threads, because
+        too many nfsd threads had been recently woken but could not get
+        enough CPU time to actually run.
+
+        This statistic counts a circumstance where the sunrpc layer
+        heuristically avoids overloading the CPU scheduler with too many
+        runnable nfsd threads.  The ideal rate of change for this counter
+        is zero.  Significant non-zero values indicate that the workload
+        is CPU limited.  Usually this is associated with heavy CPU usage
+        on all the CPUs in the nfsd thread pool.
+
+        If a sustained large overloads-avoided rate is detected on a pool,
+        the top(1) utility should be used to check for the following
+        pattern of CPU usage on all the CPUs associated with the given
+        nfsd thread pool.
+
+         - %us ~= 0 (as you're *NOT* running applications on your NFS server)
+
+         - %wa ~= 0
+
+         - %id ~= 0
+
+         - %sy + %hi + %si ~= 100
+
+        If this pattern is seen, configuring more nfsd threads will *not*
+        improve the performance of the workload.  If this patten is not
+        seen, then something more subtle is wrong.
+
+threads-timedout
+        Counts how many times an nfsd thread triggered an idle timeout,
+        i.e. was not woken to handle any incoming network packets for
+        some time.
+
+        This statistic counts a circumstance where there are more nfsd
+        threads configured than can be used by the NFS workload.  This is
+        a clue that the number of nfsd threads can be reduced without
+        affecting performance.  Unfortunately, it's only a clue and not
+        a strong indication, for a couple of reasons:
+
+         - Currently the rate at which the counter is incremented is quite
+           slow; the idle timeout is 60 minutes.  Unless the NFS workload
+           remains constant for hours at a time, this counter is unlikely
+           to be providing information that is still useful.
+
+         - It is usually a wise policy to provide some slack,
+           i.e. configure a few more nfsds than are currently needed,
+           to allow for future spikes in load.
+
+
+Note that incoming packets on NFS transports will be dealt with in
+one of three ways.  An nfsd thread can be woken (threads-woken counts
+this case), or the transport can be enqueued for later attention
+(sockets-enqueued counts this case), or the packet can be temporarily
+deferred because the transport is currently being used by an nfsd
+thread.  This last case is not very interesting and is not explicitly
+counted, but can be inferred from the other counters thus:
+
+packets-deferred = packets-arrived - ( sockets-enqueued + threads-woken )
+
+
+More
+----
+Descriptions of the other statistics file should go here.
+
+
+Greg Banks <gnb@sgi.com>
+26 Mar 2009
diff --git a/Documentation/filesystems/nfs/rpc-cache.txt b/Documentation/filesystems/nfs/rpc-cache.txt
new file mode 100644
index 000000000000..8a382bea6808
--- /dev/null
+++ b/Documentation/filesystems/nfs/rpc-cache.txt
@@ -0,0 +1,202 @@
+        This document gives a brief introduction to the caching
+mechanisms in the sunrpc layer that is used, in particular,
+for NFS authentication.
+
+CACHES
+======
+The caching replaces the old exports table and allows for
+a wide variety of values to be caches.
+
+There are a number of caches that are similar in structure though
+quite possibly very different in content and use.  There is a corpus
+of common code for managing these caches.
+
+Examples of caches that are likely to be needed are:
+  - mapping from IP address to client name
+  - mapping from client name and filesystem to export options
+  - mapping from UID to list of GIDs, to work around NFS's limitation
+    of 16 gids.
+  - mappings between local UID/GID and remote UID/GID for sites that
+    do not have uniform uid assignment
+  - mapping from network identify to public key for crypto authentication.
+
+The common code handles such things as:
+   - general cache lookup with correct locking
+   - supporting 'NEGATIVE' as well as positive entries
+   - allowing an EXPIRED time on cache items, and removing
+     items after they expire, and are no longer in-use.
+   - making requests to user-space to fill in cache entries
+   - allowing user-space to directly set entries in the cache
+   - delaying RPC requests that depend on as-yet incomplete
+     cache entries, and replaying those requests when the cache entry
+     is complete.
+   - clean out old entries as they expire.
+
+Creating a Cache
+----------------
+
+1/ A cache needs a datum to store.  This is in the form of a
+   structure definition that must contain a
+     struct cache_head
+   as an element, usually the first.
+   It will also contain a key and some content.
+   Each cache element is reference counted and contains
+   expiry and update times for use in cache management.
+2/ A cache needs a "cache_detail" structure that
+   describes the cache.  This stores the hash table, some
+   parameters for cache management, and some operations detailing how
+   to work with particular cache items.
+   The operations requires are:
+        struct cache_head *alloc(void)
+                This simply allocates appropriate memory and returns
+                a pointer to the cache_detail embedded within the
+                structure
+        void cache_put(struct kref *)
+                This is called when the last reference to an item is
+                dropped.  The pointer passed is to the 'ref' field
+                in the cache_head.  cache_put should release any
+                references create by 'cache_init' and, if CACHE_VALID
+                is set, any references created by cache_update.
+                It should then release the memory allocated by
+                'alloc'.
+        int match(struct cache_head *orig, struct cache_head *new)
+                test if the keys in the two structures match.  Return
+                1 if they do, 0 if they don't.
+        void init(struct cache_head *orig, struct cache_head *new)
+                Set the 'key' fields in 'new' from 'orig'.  This may
+                include taking references to shared objects.
+        void update(struct cache_head *orig, struct cache_head *new)
+                Set the 'content' fileds in 'new' from 'orig'.
+        int cache_show(struct seq_file *m, struct cache_detail *cd,
+                        struct cache_head *h)
+                Optional.  Used to provide a /proc file that lists the
+                contents of a cache.  This should show one item,
+                usually on just one line.
+        int cache_request(struct cache_detail *cd, struct cache_head *h,
+                char **bpp, int *blen)
+                Format a request to be send to user-space for an item
+                to be instantiated.  *bpp is a buffer of size *blen.
+                bpp should be moved forward over the encoded message,
+                and  *blen should be reduced to show how much free
+                space remains.  Return 0 on success or <0 if not
+                enough room or other problem.
+        int cache_parse(struct cache_detail *cd, char *buf, int len)
+                A message from user space has arrived to fill out a
+                cache entry.  It is in 'buf' of length 'len'.
+                cache_parse should parse this, find the item in the
+                cache with sunrpc_cache_lookup, and update the item
+                with sunrpc_cache_update.
+
+
+3/ A cache needs to be registered using cache_register().  This
+   includes it on a list of caches that will be regularly
+   cleaned to discard old data.
+
+Using a cache
+-------------
+
+To find a value in a cache, call sunrpc_cache_lookup passing a pointer
+to the cache_head in a sample item with the 'key' fields filled in.
+This will be passed to ->match to identify the target entry.  If no
+entry is found, a new entry will be create, added to the cache, and
+marked as not containing valid data.
+
+The item returned is typically passed to cache_check which will check
+if the data is valid, and may initiate an up-call to get fresh data.
+cache_check will return -ENOENT in the entry is negative or if an up
+call is needed but not possible, -EAGAIN if an upcall is pending,
+or 0 if the data is valid;
+
+cache_check can be passed a "struct cache_req *".  This structure is
+typically embedded in the actual request and can be used to create a
+deferred copy of the request (struct cache_deferred_req).  This is
+done when the found cache item is not uptodate, but the is reason to
+believe that userspace might provide information soon.  When the cache
+item does become valid, the deferred copy of the request will be
+revisited (->revisit).  It is expected that this method will
+reschedule the request for processing.
+
+The value returned by sunrpc_cache_lookup can also be passed to
+sunrpc_cache_update to set the content for the item.  A second item is
+passed which should hold the content.  If the item found by _lookup
+has valid data, then it is discarded and a new item is created.  This
+saves any user of an item from worrying about content changing while
+it is being inspected.  If the item found by _lookup does not contain
+valid data, then the content is copied across and CACHE_VALID is set.
+
+Populating a cache
+------------------
+
+Each cache has a name, and when the cache is registered, a directory
+with that name is created in /proc/net/rpc
+
+This directory contains a file called 'channel' which is a channel
+for communicating between kernel and user for populating the cache.
+This directory may later contain other files of interacting
+with the cache.
+
+The 'channel' works a bit like a datagram socket. Each 'write' is
+passed as a whole to the cache for parsing and interpretation.
+Each cache can treat the write requests differently, but it is
+expected that a message written will contain:
+  - a key
+  - an expiry time
+  - a content.
+with the intention that an item in the cache with the give key
+should be create or updated to have the given content, and the
+expiry time should be set on that item.
+
+Reading from a channel is a bit more interesting.  When a cache
+lookup fails, or when it succeeds but finds an entry that may soon
+expire, a request is lodged for that cache item to be updated by
+user-space.  These requests appear in the channel file.
+
+Successive reads will return successive requests.
+If there are no more requests to return, read will return EOF, but a
+select or poll for read will block waiting for another request to be
+added.
+
+Thus a user-space helper is likely to:
+  open the channel.
+    select for readable
+    read a request
+    write a response
+  loop.
+
+If it dies and needs to be restarted, any requests that have not been
+answered will still appear in the file and will be read by the new
+instance of the helper.
+
+Each cache should define a "cache_parse" method which takes a message
+written from user-space and processes it.  It should return an error
+(which propagates back to the write syscall) or 0.
+
+Each cache should also define a "cache_request" method which
+takes a cache item and encodes a request into the buffer
+provided.
+
+Note: If a cache has no active readers on the channel, and has had not
+active readers for more than 60 seconds, further requests will not be
+added to the channel but instead all lookups that do not find a valid
+entry will fail.  This is partly for backward compatibility: The
+previous nfs exports table was deemed to be authoritative and a
+failed lookup meant a definite 'no'.
+
+request/response format
+-----------------------
+
+While each cache is free to use it's own format for requests
+and responses over channel, the following is recommended as
+appropriate and support routines are available to help:
+Each request or response record should be printable ASCII
+with precisely one newline character which should be at the end.
+Fields within the record should be separated by spaces, normally one.
+If spaces, newlines, or nul characters are needed in a field they
+much be quoted.  two mechanisms are available:
+1/ If a field begins '\x' then it must contain an even number of
+   hex digits, and pairs of these digits provide the bytes in the
+   field.
+2/ otherwise a \ in the field must be followed by 3 octal digits
+   which give the code for a byte.  Other characters are treated
+   as them selves.  At the very least, space, newline, nul, and
+   '\' must be quoted in this way.