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When NFSD_IO_DIRECT is selected via the
/sys/kernel/debug/nfsd/io_cache_write experimental tunable, split
incoming unaligned NFS WRITE requests into a prefix, middle and
suffix segment, as needed. The middle segment is now DIO-aligned and
the prefix and/or suffix are unaligned. Synchronous buffered IO is
used for the unaligned segments, and IOCB_DIRECT is used for the
middle DIO-aligned extent.
Although IOCB_DIRECT avoids the use of the page cache, by itself it
doesn't guarantee data durability. For UNSTABLE WRITE requests,
durability is obtained by a subsequent NFS COMMIT request.
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
Co-developed-by: Chuck Lever <chuck.lever@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
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Add an experimental option that forces NFS READ operations to use
direct I/O instead of reading through the NFS server's page cache.
There is already at least one other layer of read caching: the page
cache on NFS clients.
The server's page cache, in many cases, is unlikely to provide
additional benefit. Some benchmarks have demonstrated that the
server's page cache is actively detrimental for workloads whose
working set is larger than the server's available physical memory.
For instance, on small NFS servers, cached NFS file content can
squeeze out local memory consumers. For large sequential workloads,
an enormous amount of data flows into and out of the page cache
and is consumed by NFS clients exactly once -- caching that data
is expensive to do and totally valueless.
For now this is a hidden option that can be enabled on test
systems for benchmarking. In the longer term, this option might
be enabled persistently or per-export. When the exported file
system does not support direct I/O, NFSD falls back to using
either DONTCACHE or buffered I/O to fulfill NFS READ requests.
Suggested-by: Mike Snitzer <snitzer@kernel.org>
Reviewed-by: Mike Snitzer <snitzer@kernel.org>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: NeilBrown <neil@brown.name>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
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Add 'io_cache_read' to NFSD's debugfs interface so that any data
read by NFSD will either be:
- cached using page cache (NFSD_IO_BUFFERED=0)
- cached but removed from the page cache upon completion
(NFSD_IO_DONTCACHE=1).
io_cache_read may be set by writing to:
/sys/kernel/debug/nfsd/io_cache_read
Add 'io_cache_write' to NFSD's debugfs interface so that any data
written by NFSD will either be:
- cached using page cache (NFSD_IO_BUFFERED=0)
- cached but removed from the page cache upon completion
(NFSD_IO_DONTCACHE=1).
io_cache_write may be set by writing to:
/sys/kernel/debug/nfsd/io_cache_write
The default value for both settings is NFSD_IO_BUFFERED, which is
NFSD's existing behavior for both read and write. Changes to these
settings take immediate effect for all exports and NFS versions.
Currently only xfs and ext4 implement RWF_DONTCACHE. For file
systems that do not implement RWF_DONTCACHE, NFSD use only buffered
I/O when the io_cache setting is NFSD_IO_DONTCACHE.
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
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The result of integer comparison already evaluates to bool. No need for
explicit conversion.
Signed-off-by: Xichao Zhao <zhao.xichao@vivo.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
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NFSD currently has two separate code paths for handling read
requests. One uses page splicing; the other is a traditional read
based on an iov iterator.
Because most Linux file systems support splice read, the latter
does not get nearly the same test experience as splice reads.
To force the use of vectored reads for testing and benchmarking,
introduce the ability to disable splice reads for all NFS READ
operations.
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
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Create a small sandbox under /sys/kernel/debug for experimental NFS
server feature settings. There is no API/ABI compatibility guarantee
for these settings.
The only documentation for such settings, if any documentation exists,
is in the kernel source code.
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
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