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Re-enabling NFSv3 LOCALIO is made more complex (than NFSv4) because v3
is stateless. As such, the hueristic used to identify a LOCALIO probe
point is more adhoc by nature: if/when NFSv3 client IO begins to
complete again in terms of normal RPC-based NFSv3 server IO, attempt
nfs_local_probe_async().
Care is taken to throttle the frequency of nfs_local_probe_async(),
otherwise there could be a flood of repeat calls to
nfs_local_probe_async().
The throttle is admin controlled using a new module parameter for
nfsv3, e.g.:
echo 512 > /sys/module/nfsv3/parameters/nfs3_localio_probe_throttle
Probe for NFSv3 LOCALIO every N IO requests (512 in this case). Must
be power-of-2, defaults to 0 (probing disabled).
On systems that expect to use LOCALIO with NFSv3 the admin should
configure the 'nfs3_localio_probe_throttle' module parameter.
This commit backfills module parameter documentation in localio.rst
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>
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Also update Documentation/filesystems/nfs/localio.rst accordingly
and reduce the technical documentation debt that was previously
captured in that document.
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Acked-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>
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This commit simply adds the required O_DIRECT plumbing. It doesn't
address the fact that NFS doesn't ensure all writes are page aligned
(nor device logical block size aligned as required by O_DIRECT).
Because NFS will read-modify-write for IO that isn't aligned, LOCALIO
will not use O_DIRECT semantics by default if/when an application
requests the use of O_DIRECT. Allow the use of O_DIRECT semantics by:
1: Adding a flag to the nfs_pgio_header struct to allow the NFS
O_DIRECT layer to signal that O_DIRECT was used by the application
2: Adding a 'localio_O_DIRECT_semantics' NFS module parameter that
when enabled will cause LOCALIO to use O_DIRECT semantics (this may
cause IO to fail if applications do not properly align their IO).
This commit is derived from code developed by Weston Andros Adamson.
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>
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Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Fixes: 92945bd81ca4 ("nfs: add Documentation/filesystems/nfs/localio.rst")
Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>
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This section answers a new FAQ entry:
9. How does LOCALIO make certain that object lifetimes are managed
properly given NFSD and NFS operate in different contexts?
See the detailed "NFS Client and Server Interlock" section below.
The first half of the section details NeilBrown's elegant design
for LOCALIO's nfs_uuid_t based interlock and is heavily based on
Neil's "net namespace refcounting" description here:
https://marc.info/?l=linux-nfs&m=172498546024767&w=2
The second half of the section details the per-cpu-refcount introduced
to ensure NFSD's nfsd_serv isn't destroyed while in use by a LOCALIO
client.
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
Reviewed-by: NeilBrown <neilb@suse.de>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>
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Add a FAQ section to give answers to questions that have been raised
during review of the localio feature.
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Co-developed-by: Mike Snitzer <snitzer@kernel.org>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
Reviewed-by: NeilBrown <neilb@suse.de>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>
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This document gives an overview of the LOCALIO auxiliary RPC protocol
added to the Linux NFS client and server to allow them to reliably
handshake to determine if they are on the same host.
Once an NFS client and server handshake as "local", the client will
bypass the network RPC protocol for read, write and commit operations.
Due to this XDR and RPC bypass, these operations will operate faster.
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
Reviewed-by: NeilBrown <neilb@suse.de>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>
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