linux-toradex.git/fs/netfs/Makefile, branch master

netfs: Add support for caching single monolithic objects such as AFS dirs

2024-12-20T21:34:06+00:00

Add support for caching the content of a file that contains a single
monolithic object that must be read/written with a single I/O operation,
such as an AFS directory.

Signed-off-by: David Howells 
Link: https://lore.kernel.org/r/20241216204124.3752367-20-dhowells@redhat.com
cc: Jeff Layton 
cc: Marc Dionne 
cc: netfs@lists.linux.dev
cc: linux-afs@lists.infradead.org
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Christian Brauner

netfs: Split retry code out of fs/netfs/write_collect.c

2024-12-20T21:34:03+00:00

Split write-retry code out of fs/netfs/write_collect.c as it will become
more elaborate when content crypto is introduced.

Signed-off-by: David Howells 
Link: https://lore.kernel.org/r/20241216204124.3752367-8-dhowells@redhat.com
cc: Jeff Layton 
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Christian Brauner

netfs: Abstract out a rolling folio buffer implementation

2024-12-20T21:34:02+00:00

A rolling buffer is a series of folios held in a list of folio_queues.  New
folios and folio_queue structs may be inserted at the head simultaneously
with spent ones being removed from the tail without the need for locking.

The rolling buffer includes an iov_iter and it has to be careful managing
this as the list of folio_queues is extended such that an oops doesn't
incurred because the iterator was pointing to the end of a folio_queue
segment that got appended to and then removed.

We need to use the mechanism twice, once for read and once for write, and,
in future patches, we will use a second rolling buffer to handle bounce
buffering for content encryption.

Signed-off-by: David Howells 
Link: https://lore.kernel.org/r/20241216204124.3752367-6-dhowells@redhat.com
cc: Jeff Layton 
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Christian Brauner

netfs: Speed up buffered reading

2024-09-12T10:20:41+00:00

Improve the efficiency of buffered reads in a number of ways:

 (1) Overhaul the algorithm in general so that it's a lot more compact and
     split the read submission code between buffered and unbuffered
     versions.  The unbuffered version can be vastly simplified.

 (2) Read-result collection is handed off to a work queue rather than being
     done in the I/O thread.  Multiple subrequests can be processes
     simultaneously.

 (3) When a subrequest is collected, any folios it fully spans are
     collected and "spare" data on either side is donated to either the
     previous or the next subrequest in the sequence.

Notes:

 (*) Readahead expansion is massively slows down fio, presumably because it
     causes a load of extra allocations, both folio and xarray, up front
     before RPC requests can be transmitted.

 (*) RDMA with cifs does appear to work, both with SIW and RXE.

 (*) PG_private_2-based reading and copy-to-cache is split out into its own
     file and altered to use folio_queue.  Note that the copy to the cache
     now creates a new write transaction against the cache and adds the
     folios to be copied into it.  This allows it to use part of the
     writeback I/O code.

Signed-off-by: David Howells 
cc: Jeff Layton 
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
Link: https://lore.kernel.org/r/20240814203850.2240469-20-dhowells@redhat.com/ # v2
Signed-off-by: Christian Brauner

netfs: Cut over to using new writeback code

2024-05-01T17:07:37+00:00

Cut over to using the new writeback code.  The old code is #ifdef'd out or
otherwise removed from compilation to avoid conflicts and will be removed
in a future patch.

Signed-off-by: David Howells 
Reviewed-by: Jeff Layton 
cc: Eric Van Hensbergen 
cc: Latchesar Ionkov 
cc: Dominique Martinet 
cc: Christian Schoenebeck 
cc: Marc Dionne 
cc: v9fs@lists.linux.dev
cc: linux-afs@lists.infradead.org
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org

netfs: New writeback implementation

2024-05-01T17:07:36+00:00

The current netfslib writeback implementation creates writeback requests of
contiguous folio data and then separately tiles subrequests over the space
twice, once for the server and once for the cache.  This creates a few
issues:

 (1) Every time there's a discontiguity or a change between writing to only
     one destination or writing to both, it must create a new request.
     This makes it harder to do vectored writes.

 (2) The folios don't have the writeback mark removed until the end of the
     request - and a request could be hundreds of megabytes.

 (3) In future, I want to support a larger cache granularity, which will
     require aggregation of some folios that contain unmodified data (which
     only need to go to the cache) and some which contain modifications
     (which need to be uploaded and stored to the cache) - but, currently,
     these are treated as discontiguous.

There's also a move to get everyone to use writeback_iter() to extract
writable folios from the pagecache.  That said, currently writeback_iter()
has some issues that make it less than ideal:

 (1) there's no way to cancel the iteration, even if you find a "temporary"
     error that means the current folio and all subsequent folios are going
     to fail;

 (2) there's no way to filter the folios being written back - something
     that will impact Ceph with it's ordered snap system;

 (3) and if you get a folio you can't immediately deal with (say you need
     to flush the preceding writes), you are left with a folio hanging in
     the locked state for the duration, when really we should unlock it and
     relock it later.

In this new implementation, I use writeback_iter() to pump folios,
progressively creating two parallel, but separate streams and cleaning up
the finished folios as the subrequests complete.  Either or both streams
can contain gaps, and the subrequests in each stream can be of variable
size, don't need to align with each other and don't need to align with the
folios.

Indeed, subrequests can cross folio boundaries, may cover several folios or
a folio may be spanned by multiple folios, e.g.:

         +---+---+-----+-----+---+----------+
Folios:  |   |   |     |     |   |          |
         +---+---+-----+-----+---+----------+

           +------+------+     +----+----+
Upload:    |      |      |.....|    |    |
           +------+------+     +----+----+

         +------+------+------+------+------+
Cache:   |      |      |      |      |      |
         +------+------+------+------+------+

The progressive subrequest construction permits the algorithm to be
preparing both the next upload to the server and the next write to the
cache whilst the previous ones are already in progress.  Throttling can be
applied to control the rate of production of subrequests - and, in any
case, we probably want to write them to the server in ascending order,
particularly if the file will be extended.

Content crypto can also be prepared at the same time as the subrequests and
run asynchronously, with the prepped requests being stalled until the
crypto catches up with them.  This might also be useful for transport
crypto, but that happens at a lower layer, so probably would be harder to
pull off.

The algorithm is split into three parts:

 (1) The issuer.  This walks through the data, packaging it up, encrypting
     it and creating subrequests.  The part of this that generates
     subrequests only deals with file positions and spans and so is usable
     for DIO/unbuffered writes as well as buffered writes.

 (2) The collector. This asynchronously collects completed subrequests,
     unlocks folios, frees crypto buffers and performs any retries.  This
     runs in a work queue so that the issuer can return to the caller for
     writeback (so that the VM can have its kswapd thread back) or async
     writes.

 (3) The retryer.  This pauses the issuer, waits for all outstanding
     subrequests to complete and then goes through the failed subrequests
     to reissue them.  This may involve reprepping them (with cifs, the
     credits must be renegotiated, and a subrequest may need splitting),
     and doing RMW for content crypto if there's a conflicting change on
     the server.

[!] Note that some of the functions are prefixed with "new_" to avoid
clashes with existing functions.  These will be renamed in a later patch
that cuts over to the new algorithm.

Signed-off-by: David Howells 
Reviewed-by: Jeff Layton 
cc: Eric Van Hensbergen 
cc: Latchesar Ionkov 
cc: Dominique Martinet 
cc: Christian Schoenebeck 
cc: Marc Dionne 
cc: v9fs@lists.linux.dev
cc: linux-afs@lists.infradead.org
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org

netfs: Implement unbuffered/DIO write support

2023-12-28T09:45:24+00:00

Implement support for unbuffered writes and direct I/O writes.  If the
write is misaligned with respect to the fscrypt block size, then RMW cycles
are performed if necessary.  DIO writes are a special case of unbuffered
writes with extra restriction imposed, such as block size alignment
requirements.

Also provide a field that can tell the code to add some extra space onto
the bounce buffer for use by the filesystem in the case of a
content-encrypted file.

Signed-off-by: David Howells 
Reviewed-by: Jeff Layton 
cc: linux-cachefs@redhat.com
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org

netfs: Implement unbuffered/DIO read support

2023-12-28T09:45:23+00:00

Implement support for unbuffered and DIO reads in the netfs library,
utilising the existing read helper code to do block splitting and
individual queuing.  The code also handles extraction of the destination
buffer from the supplied iterator, allowing async unbuffered reads to take
place.

The read will be split up according to the rsize setting and, if supplied,
the ->clamp_length() method.  Note that the next subrequest will be issued
as soon as issue_op returns, without waiting for previous ones to finish.
The network filesystem needs to pause or handle queuing them if it doesn't
want to fire them all at the server simultaneously.

Once all the subrequests have finished, the state will be assessed and the
amount of data to be indicated as having being obtained will be
determined.  As the subrequests may finish in any order, if an intermediate
subrequest is short, any further subrequests may be copied into the buffer
and then abandoned.

In the future, this will also take care of doing an unbuffered read from
encrypted content, with the decryption being done by the library.

Signed-off-by: David Howells 
cc: Jeff Layton 
cc: linux-cachefs@redhat.com
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org

netfs: Provide func to copy data to pagecache for buffered write

2023-12-28T09:45:22+00:00

Provide a netfs write helper, netfs_perform_write() to buffer data to be
written in the pagecache and mark the modified folios dirty.

It will perform "streaming writes" for folios that aren't currently
resident, if possible, storing data in partially modified folios that are
marked dirty, but not uptodate.  It will also tag pages as belonging to
fs-specific write groups if so directed by the filesystem.

This is derived from generic_perform_write(), but doesn't use
->write_begin() and ->write_end(), having that logic rolled in instead.

Signed-off-by: David Howells 
cc: Jeff Layton 
cc: linux-cachefs@redhat.com
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org

netfs: Dispatch write requests to process a writeback slice

2023-12-28T09:45:22+00:00

Dispatch one or more write reqeusts to process a writeback slice, where a
slice is tailored more to logical block divisions within the file (such as
crypto blocks, an object layout or cache granules) than the protocol RPC
maximum capacity.

The dispatch doesn't happen until throttling allows, at which point the
entire writeback slice is processed and queued.  A slice may be written to
multiple destinations (one or more servers and the local cache) and the
writes to each destination might be split up along different lines.

The writeback slice holds the required folios pinned.  An iov_iter is
provided in netfs_write_request that describes the buffer to be used.  This
may be part of the pagecache, may have auxiliary padding pages attached or
may be a bounce buffer resulting from crypto or compression.  Consequently,
the filesystem must not twiddle the folio markings directly.

The following API is available to the filesystem:

 (1) The ->create_write_requests() method is called to ask the filesystem
     to create the requests it needs.  This is passed the writeback slice
     to be processed.

 (2) The filesystem should then call netfs_create_write_request() to create
     the requests it needs.

 (3) Once a request is initialised, netfs_queue_write_request() can be
     called to dispatch it asynchronously, if not completed immediately.

 (4) netfs_write_request_completed() should be called to note the
     completion of a request.

 (5) netfs_get_write_request() and netfs_put_write_request() are provided
     to refcount a request.  These take constants from the netfs_wreq_trace
     enum for logging into ftrace.

 (6) The ->free_write_request is method is called to ask the filesystem to
     clean up a request.

Signed-off-by: David Howells 
Reviewed-by: Jeff Layton 
cc: linux-cachefs@redhat.com
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org