From 34e75cf4beb1a88a61b7c76b5fdc99c43cff8594 Mon Sep 17 00:00:00 2001 From: "Daniel W. S. Almeida" Date: Wed, 29 Jan 2020 01:49:13 -0300 Subject: Documentation: nfs: convert pnfs.txt to ReST Convert pnfs.txt to ReST. Content remains mostly unchanged. Signed-off-by: Daniel W. S. Almeida Link: https://lore.kernel.org/r/20200129044917.566906-2-dwlsalmeida@gmail.com Signed-off-by: Jonathan Corbet --- Documentation/filesystems/nfs/index.rst | 9 ++++ Documentation/filesystems/nfs/pnfs.rst | 78 +++++++++++++++++++++++++++++++++ Documentation/filesystems/nfs/pnfs.txt | 73 ------------------------------ 3 files changed, 87 insertions(+), 73 deletions(-) create mode 100644 Documentation/filesystems/nfs/index.rst create mode 100644 Documentation/filesystems/nfs/pnfs.rst delete mode 100644 Documentation/filesystems/nfs/pnfs.txt (limited to 'Documentation/filesystems/nfs') diff --git a/Documentation/filesystems/nfs/index.rst b/Documentation/filesystems/nfs/index.rst new file mode 100644 index 000000000000..d19ba592779a --- /dev/null +++ b/Documentation/filesystems/nfs/index.rst @@ -0,0 +1,9 @@ +=============================== +NFS +=============================== + + +.. toctree:: + :maxdepth: 1 + + pnfs diff --git a/Documentation/filesystems/nfs/pnfs.rst b/Documentation/filesystems/nfs/pnfs.rst new file mode 100644 index 000000000000..7c470ecdc3a9 --- /dev/null +++ b/Documentation/filesystems/nfs/pnfs.rst @@ -0,0 +1,78 @@ +========================== +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 `here. +`_ + +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 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 -- cgit v1.2.3