When memory is short, new worker threads cannot be created and we depend
on the minimum one rpciod thread to be able to handle everything.  So it
must not block waiting for memory.

xprt_dynamic_alloc_slot can block indefinitely.  This can tie up all
workqueue threads and NFS can deadlock.  So when called from a
workqueue, set __GFP_NORETRY.

The rdma alloc_slot already does not block.  However it sets the error
to -EAGAIN suggesting this will trigger a sleep.  It does not.  As we
can see in call_reserveresult(), only -ENOMEM causes a sleep.  -EAGAIN
causes immediate retry.
Signed-off-by: NNeilBrown <neilb@suse.de>
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>

When memory is short, new worker threads cannot be created and we depend
on the minimum one rpciod thread to be able to handle everything.  So it
must not block waiting for memory.

mempools are particularly a problem as memory can only be released back
to the mempool by an async rpc task running.  If all available workqueue
threads are waiting on the mempool, no thread is available to return
anything.

lookup_cred() can block on a mempool or kmalloc - and this can cause
deadlocks.  So add a new RPCAUTH_LOOKUP flag for async lookups and don't
block on memory.  If the -ENOMEM gets back to call_refreshresult(), wait
a short while and try again.  HZ>>4 is chosen as it is used elsewhere
for -ENOMEM retries.
Signed-off-by: NNeilBrown <neilb@suse.de>
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>

When memory is short, new worker threads cannot be created and we depend
on the minimum one rpciod thread to be able to handle everything.
So it must not block waiting for memory.

mempools are particularly a problem as memory can only be released back
to the mempool by an async rpc task running.  If all available
workqueue threads are waiting on the mempool, no thread is available to
return anything.

rpc_malloc() can block, and this might cause deadlocks.
So check RPC_IS_ASYNC(), rather than RPC_IS_SWAPPER() to determine if
blocking is acceptable.
Signed-off-by: NNeilBrown <neilb@suse.de>
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>

This code is pointless as IS_SWAPFILE is always defined.
So remove it.
Suggested-by: NMark Hemment <markhemm@googlemail.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NNeilBrown <neilb@suse.de>
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>

The fscache cookie APIs including fscache_acquire_cookie() and
fscache_relinquish_cookie() now have very good tracing.  Thus,
there is no real need for dfprintks in the NFS fscache interface.

The NFS fscache interface has removed all dfprintks so remove the
NFSDBG_FSCACHE defines.
Signed-off-by: NDave Wysochanski <dwysocha@redhat.com>
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>

Most of fscache and other NFS IO paths are now using tracepoints.
Remove the dfprintks in the NFS fscache read/write page functions
and replace with tracepoints at the begin and end of the functions.
Signed-off-by: NDave Wysochanski <dwysocha@redhat.com>
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>

Rename NFS fscache functions in a more consistent fashion
to better reflect when we read from and write to fscache.
Signed-off-by: NDave Wysochanski <dwysocha@redhat.com>
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>

A number of places in the fscache interface used nfs_inode when inode could
be used, simplifying the code.
Signed-off-by: NDave Wysochanski <dwysocha@redhat.com>
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>

In the presence of trunking transports, it's helpful to make sure
that during the migration event, the GETATTR for fs_location attribute
happens on the main transport.
Signed-off-by: NOlga Kornievskaia <kolga@netapp.com>
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>

[You don't often get email from khoroshilov@ispras.ru. Learn why this is important at http://aka.ms/LearnAboutSenderIdentification.]

Overflow check in not needed anymore after we switch to kmalloc_array().
Signed-off-by: NAlexey Khoroshilov <khoroshilov@ispras.ru>
Fixes: a4f743a6 ("NFSv4.1: Convert open-coded array allocation calls to kmalloc_array()")
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>

Even if we're not able to cache all the entries in the readdir buffer,
let's ensure that we do prime the dcache.
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>

Replace the 'previous cookie' field in struct nfs_entry with the
array->last_cookie.
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>

Avoid clearing the entire readdir page cache if we're just doing forced
readdirplus for the 'ls -l' heuristic.
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>

Instead of using a linear index to address the pages, use the cookie of
the first entry, since that is what we use to match the page anyway.

This allows us to avoid re-reading the entire cache on a seekdir() type
of operation. The latter is very common when re-exporting NFS, and is a
major performance drain.

The change does affect our duplicate cookie detection, since we can no
longer rely on the page index as a linear offset for detecting whether
we looped backwards. However since we no longer do a linear search
through all the pages on each call to nfs_readdir(), this is less of a
concern than it was previously.
The other downside is that invalidate_mapping_pages() no longer can use
the page index to avoid clearing pages that have been read. A subsequent
patch will restore the functionality this provides to the 'ls -l'
heuristic.
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>

Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>

Enable tracking of when the readdirplus heuristic causes a page cache
invalidation.
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>

Trace the effects of readdirplus on attribute and dentry revalidation.
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>

Add tracing to track how often the client goes to the server for updated
readdir information.
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>

If the revalidation was forced, due to the presence of a LOOKUP_EXCL or
a LOOKUP_REVAL flag, then readdirplus won't help. It also can't help
when we're doing a path component lookup.
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>

If the filesystem is case insensitive, then readdirplus can't help with
cache misses, since it won't return case folded variants of the filename.
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>

Instead of pretending that we know the ratio of directory info vs
readdirplus attribute info, just set the 'dircount' field to the same
value as the 'maxcount' field.
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>

If attribute caching is turned off, then use of readdirplus is not going
to help stat() performance.
Readdirplus also doesn't help if a file is being written to, since we
will have to flush those writes in order to sync the mtime/ctime.
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>

The heuristic for readdirplus is designed to try to detect 'ls -l' and
similar patterns. It does so by looking for cache hit/miss patterns in
both the attribute cache and in the dcache of the files in a given
directory, and then sets a flag for the readdirplus code to interpret.

The problem with this approach is that a single attribute or dcache miss
can cause the NFS code to force a refresh of the attributes for the
entire set of files contained in the directory.

To be able to make a more nuanced decision, let's sample the number of
hits and misses in the set of open directory descriptors. That allows us
to set thresholds at which we start preferring READDIRPLUS over regular
READDIR, or at which we start to force a re-read of the remaining
readdir cache using READDIRPLUS.
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>

When reading a very large directory, we want to try to keep the page
cache up to date if doing so is inexpensive. With the change to allow
readdir to continue reading even when the cache is incomplete, we no
longer need to fall back to uncached readdir in order to scale to large
directories.
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>

Recent changes to readdir mean that we can cope with partially filled
page cache entries, so we no longer need to rely on looping in
nfs_readdir_xdr_to_array().
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>

Ensure that if the cookie verifier changes when we use the zero-valued
cookie, then we invalidate any cached pages.
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>

The current NFS readdir code will always try to maximise the amount of
readahead it performs on the assumption that we can cache anything that
isn't immediately read by the process.
There are several cases where this assumption breaks down, including
when the 'ls -l' heuristic kicks in to try to force use of readdirplus
as a batch replacement for lookup/getattr.

This patch therefore tries to tone down the amount of readahead we
perform, and adjust it to try to match the amount of data being
requested by user space.
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>

When we hit the end of the data in the readdir page, we don't want to
start filling a new page, unless this one is full.
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>

If the page cache entry that was last read gets invalidated for some
reason, then make sure we can re-create it on the next call to readdir.
This, combined with the cache page validation, allows us to reuse the
cached value of page-index on successive calls to nfs_readdir.

Credit is due to Benjamin Coddington for showing that the concept works,
and that it allows for improved cache sharing between processes even in
the case where pages are lost due to LRU or active invalidation.
Suggested-by: NBenjamin Coddington <bcodding@redhat.com>
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>

Use the change attribute and the first cookie in a directory page cache
entry to validate that the page is up to date.
Suggested-by: NBenjamin Coddington <bcodding@redhat.com>
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>

Instead of relying on counting the page offsets as we walk through the
page cache, switch to calculating them algorithmically.
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>

Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>

For the purpose of ensuring that opendir() followed by seekdir() work as
correctly as possible, try to initialise the readdir verifier in
nfs_opendir().
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>

Enable tracing of lookup revalidation failures.
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>

Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>

Valid return values for decode_dirent() callback functions are:
 0: Success
 -EBADCOOKIE: End of directory
 -EAGAIN: End of xdr_stream

All errors need to map into one of those three values.

Fixes: 573c4e1e ("NFS: Simplify ->decode_dirent() calling sequence")
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>

This reverts commit 50c790a0.

The functionality is believed to be capable of causing regressions in
existing setups, so the author has requested that it be reverted.
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>

The use of mapping_set_error() in conjunction with calls to
filemap_check_errors() is problematic because every error gets reported
as either an EIO or an ENOSPC by filemap_check_errors() in functions
such as filemap_write_and_wait() or filemap_write_and_wait_range().
In almost all cases, we prefer to use the more nuanced wb errors.

Fixes: b8946d7b ("NFS: Revalidate the file mapping on all fatal writeback errors")
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>

Add a helper for the xattr mask so that we can get rid of the inlined
ifdefs.
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>

We should never expect the 'xattr_cache' to be non-null in that case,
hence nfs_set_cache_invalid() is just going to optimise it away.
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>