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Diffstat (limited to 'Documentation/filesystems/nfs/pnfs.txt')
| -rw-r--r-- | Documentation/filesystems/nfs/pnfs.txt | 73 |
1 files changed, 0 insertions, 73 deletions
diff --git a/Documentation/filesystems/nfs/pnfs.txt b/Documentation/filesystems/nfs/pnfs.txt deleted file mode 100644 index 80dc0bdc302a..000000000000 --- a/Documentation/filesystems/nfs/pnfs.txt +++ /dev/null @@ -1,73 +0,0 @@ -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 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. - -lseg ----- -lseg maintains an extra reference corresponding to the NFS_LSEG_VALID -bit which holds it in the pnfs_layout_hdr's list. When the final lseg -is removed from the pnfs_layout_hdr's list, the NFS_LAYOUT_DESTROYED -bit is set, preventing any new lsegs from being added. - -layout drivers --------------- - -PNFS utilizes what is called layout drivers. The STD defines 4 basic -layout types: "files", "objects", "blocks", and "flexfiles". For each -of these types there is a layout-driver with a common function-vectors -table which are called by the nfs-client pnfs-core to implement the -different layout types. - -Files-layout-driver code is in: fs/nfs/filelayout/.. directory -Blocks-layout-driver code is in: fs/nfs/blocklayout/.. directory -Flexfiles-layout-driver code is in: fs/nfs/flexfilelayout/.. directory - -blocks-layout setup -------------------- - -TODO: Document the setup needs of the blocks layout driver |