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authorLinus Torvalds <torvalds@linux-foundation.org>2010-10-26 09:52:09 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2010-10-26 09:52:09 -0700
commita4dd8dce14014665862ce7911b38cb2c69e366dd (patch)
tree00e79b2845d5d49abcd83cf253db83a52d482265 /Documentation
parentb18cae4224bde7e5a332c19bc99247b2098ea232 (diff)
parent411b5e05617593efebc06241dbc56f42150f2abe (diff)
Merge branch 'nfs-for-2.6.37' of git://git.linux-nfs.org/projects/trondmy/nfs-2.6
* 'nfs-for-2.6.37' of git://git.linux-nfs.org/projects/trondmy/nfs-2.6: net/sunrpc: Use static const char arrays nfs4: fix channel attribute sanity-checks NFSv4.1: Use more sensible names for 'initialize_mountpoint' NFSv4.1: pnfs: filelayout: add driver's LAYOUTGET and GETDEVICEINFO infrastructure NFSv4.1: pnfs: add LAYOUTGET and GETDEVICEINFO infrastructure NFS: client needs to maintain list of inodes with active layouts NFS: create and destroy inode's layout cache NFSv4.1: pnfs: filelayout: introduce minimal file layout driver NFSv4.1: pnfs: full mount/umount infrastructure NFS: set layout driver NFS: ask for layouttypes during v4 fsinfo call NFS: change stateid to be a union NFSv4.1: pnfsd, pnfs: protocol level pnfs constants SUNRPC: define xdr_decode_opaque_fixed NFSD: remove duplicate NFS4_STATEID_SIZE
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/filesystems/nfs/00-INDEX2
-rw-r--r--Documentation/filesystems/nfs/pnfs.txt48
2 files changed, 50 insertions, 0 deletions
diff --git a/Documentation/filesystems/nfs/00-INDEX b/Documentation/filesystems/nfs/00-INDEX
index 3225a566211..a57e12411d2 100644
--- a/Documentation/filesystems/nfs/00-INDEX
+++ b/Documentation/filesystems/nfs/00-INDEX
@@ -12,6 +12,8 @@ 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.
+pnfs.txt
+ - short explanation of some of the internals of the pnfs client code
rpc-cache.txt
- introduction to the caching mechanisms in the sunrpc layer.
idmapper.txt
diff --git a/Documentation/filesystems/nfs/pnfs.txt b/Documentation/filesystems/nfs/pnfs.txt
new file mode 100644
index 00000000000..bc0b9cfe095
--- /dev/null
+++ b/Documentation/filesystems/nfs/pnfs.txt
@@ -0,0 +1,48 @@
+Reference counting in pnfs:
+==========================
+
+The are several inter-related caches. We have layouts which can
+reference multiple devices, each of which can reference multiple data servers.
+Each data server can be referenced by multiple devices. Each device
+can be referenced by multiple layouts. To keep all of this straight,
+we need to reference count.
+
+
+struct pnfs_layout_hdr
+----------------------
+The on-the-wire command LAYOUTGET corresponds to struct
+pnfs_layout_segment, usually referred to by the variable name lseg.
+Each nfs_inode may hold a pointer to a cache of of these layout
+segments in nfsi->layout, of type struct pnfs_layout_hdr.
+
+We reference the header for the inode pointing to it, across each
+outstanding RPC call that references it (LAYOUTGET, LAYOUTRETURN,
+LAYOUTCOMMIT), and for each lseg held within.
+
+Each header is also (when non-empty) put on a list associated with
+struct nfs_client (cl_layouts). Being put on this list does not bump
+the reference count, as the layout is kept around by the lseg that
+keeps it in the list.
+
+deviceid_cache
+--------------
+lsegs reference device ids, which are resolved per nfs_client and
+layout driver type. The device ids are held in a RCU cache (struct
+nfs4_deviceid_cache). The cache itself is referenced across each
+mount. The entries (struct nfs4_deviceid) themselves are held across
+the lifetime of each lseg referencing them.
+
+RCU is used because the deviceid is basically a write once, read many
+data structure. The hlist size of 32 buckets needs better
+justification, but seems reasonable given that we can have multiple
+deviceid's per filesystem, and multiple filesystems per nfs_client.
+
+The hash code is copied from the nfsd code base. A discussion of
+hashing and variations of this algorithm can be found at:
+http://groups.google.com/group/comp.lang.c/browse_thread/thread/9522965e2b8d3809
+
+data server cache
+-----------------
+file driver devices refer to data servers, which are kept in a module
+level cache. Its reference is held over the lifetime of the deviceid
+pointing to it.