Merge branch 'netfs-writeback' of ssh://gitolite.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs

Pull netfs writeback updates from David Howells:

The primary purpose of these patches is to rework the netfslib writeback
implementation such that pages read from the cache are written to the cache
through ->writepages(), thereby allowing the fscache page flag to be
retired.

The reworking also:

 (1) builds on top of the new writeback_iter() infrastructure;

 (2) makes it possible to use vectored write RPCs as discontiguous streams
     of pages can be accommodated;

 (3) makes it easier to do simultaneous content crypto and stream division.

 (4) provides support for retrying writes and re-dividing a stream;

 (5) replaces the ->launder_folio() op, so that ->writepages() is used
     instead;

 (6) uses mempools to allocate the netfs_io_request and netfs_io_subrequest
     structs to avoid allocation failure in the writeback path.

Some code that uses the fscache page flag is retained for compatibility
purposes with nfs and ceph.  The code is switched to using the synonymous
private_2 label instead and marked with deprecation comments.  I have a
separate set of patches that convert cifs to use this code.

-~-

In this new implementation, writeback_iter() is used to pump folios,
progressively creating two parallel, but separate streams.  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.  (Note that more streams can be added if we have multiple
servers to duplicate data to).

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

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

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

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

Data that got read from the server that needs copying to the cache is
stored in folios that are marked dirty and have folio->private set to a
special value.

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.

     Collection is slightly complex as the collector has to work out where
     discontiguities happen in the folio list so that it doesn't try and
     collect folios that weren't included in the write out.

 (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.

* 'netfs-writeback' of ssh://gitolite.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs: (22 commits)
  netfs, afs: Use writeback retry to deal with alternate keys
  netfs: Miscellaneous tidy ups
  netfs: Remove the old writeback code
  netfs: Cut over to using new writeback code
  netfs, cachefiles: Implement helpers for new write code
  netfs, 9p: Implement helpers for new write code
  netfs, afs: Implement helpers for new write code
  netfs: Add some write-side stats and clean up some stat names
  netfs: New writeback implementation
  netfs: Switch to using unsigned long long rather than loff_t
  mm: Export writeback_iter()
  netfs: Use mempools for allocating requests and subrequests
  netfs: Remove ->launder_folio() support
  afs: Use alternative invalidation to using launder_folio
  9p: Use alternative invalidation to using launder_folio
  mm: Provide a means of invalidation without using launder_folio
  netfs: Use subreq_counter to allocate subreq debug_index values
  netfs: Make netfs_io_request::subreq_counter an atomic_t
  netfs: Remove deprecated use of PG_private_2 as a second writeback flag
  mm: Remove the PG_fscache alias for PG_private_2
  ...

Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: brauner

fs/9p/vfs_addr.c

@@ -26,36 +26,38 @@
 #include "cache.h"
 #include "fid.h"
 
-static void v9fs_upload_to_server(struct netfs_io_subrequest *subreq)
+/*
+ * Writeback calls this when it finds a folio that needs uploading.  This isn't
+ * called if writeback only has copy-to-cache to deal with.
+ */
+static void v9fs_begin_writeback(struct netfs_io_request *wreq)
 {
-	struct p9_fid *fid = subreq->rreq->netfs_priv;
-	int err, len;
-
-	trace_netfs_sreq(subreq, netfs_sreq_trace_submit);
-	len = p9_client_write(fid, subreq->start, &subreq->io_iter, &err);
-	netfs_write_subrequest_terminated(subreq, len ?: err, false);
-}
+	struct p9_fid *fid;
 
-static void v9fs_upload_to_server_worker(struct work_struct *work)
-{
-	struct netfs_io_subrequest *subreq =
-		container_of(work, struct netfs_io_subrequest, work);
+	fid = v9fs_fid_find_inode(wreq->inode, true, INVALID_UID, true);
+	if (!fid) {
+		WARN_ONCE(1, "folio expected an open fid inode->i_ino=%lx\n",
+			  wreq->inode->i_ino);
+		return;
+	}
 
-	v9fs_upload_to_server(subreq);
+	wreq->wsize = fid->clnt->msize - P9_IOHDRSZ;
+	if (fid->iounit)
+		wreq->wsize = min(wreq->wsize, fid->iounit);
+	wreq->netfs_priv = fid;
+	wreq->io_streams[0].avail = true;
 }
 
 /*
- * Set up write requests for a writeback slice.  We need to add a write request
- * for each write we want to make.
+ * Issue a subrequest to write to the server.
  */
-static void v9fs_create_write_requests(struct netfs_io_request *wreq, loff_t start, size_t len)
+static void v9fs_issue_write(struct netfs_io_subrequest *subreq)
 {
-	struct netfs_io_subrequest *subreq;
+	struct p9_fid *fid = subreq->rreq->netfs_priv;
+	int err, len;
 
-	subreq = netfs_create_write_request(wreq, NETFS_UPLOAD_TO_SERVER,
-					    start, len, v9fs_upload_to_server_worker);
-	if (subreq)
-		netfs_queue_write_request(subreq);
+	len = p9_client_write(fid, subreq->start, &subreq->io_iter, &err);
+	netfs_write_subrequest_terminated(subreq, len ?: err, false);
 }
 
 /**
@@ -87,12 +89,16 @@ static int v9fs_init_request(struct netfs_io_request *rreq, struct file *file)
 {
 	struct p9_fid *fid;
 	bool writing = (rreq->origin == NETFS_READ_FOR_WRITE ||
-			rreq->origin == NETFS_WRITEBACK ||
 			rreq->origin == NETFS_WRITETHROUGH ||
-			rreq->origin == NETFS_LAUNDER_WRITE ||
 			rreq->origin == NETFS_UNBUFFERED_WRITE ||
 			rreq->origin == NETFS_DIO_WRITE);
 
+	if (rreq->origin == NETFS_WRITEBACK)
+		return 0; /* We don't get the write handle until we find we
+			   * have actually dirty data and not just
+			   * copy-to-cache data.
+			   */
+
 	if (file) {
 		fid = file->private_data;
 		if (!fid)
@@ -104,6 +110,10 @@ static int v9fs_init_request(struct netfs_io_request *rreq, struct file *file)
 			goto no_fid;
 	}
 
+	rreq->wsize = fid->clnt->msize - P9_IOHDRSZ;
+	if (fid->iounit)
+		rreq->wsize = min(rreq->wsize, fid->iounit);
+
 	/* we might need to read from a fid that was opened write-only
 	 * for read-modify-write of page cache, use the writeback fid
 	 * for that */
@@ -132,7 +142,8 @@ const struct netfs_request_ops v9fs_req_ops = {
 	.init_request		= v9fs_init_request,
 	.free_request		= v9fs_free_request,
 	.issue_read		= v9fs_issue_read,
-	.create_write_requests	= v9fs_create_write_requests,
+	.begin_writeback	= v9fs_begin_writeback,
+	.issue_write		= v9fs_issue_write,
 };
 
 const struct address_space_operations v9fs_addr_operations = {
@@ -141,7 +152,6 @@ const struct address_space_operations v9fs_addr_operations = {
 	.dirty_folio		= netfs_dirty_folio,
 	.release_folio		= netfs_release_folio,
 	.invalidate_folio	= netfs_invalidate_folio,
-	.launder_folio		= netfs_launder_folio,
 	.direct_IO		= noop_direct_IO,
 	.writepages		= netfs_writepages,
 };

fs/afs/file.c

@@ -54,7 +54,6 @@ const struct address_space_operations afs_file_aops = {
 	.read_folio	= netfs_read_folio,
 	.readahead	= netfs_readahead,
 	.dirty_folio	= netfs_dirty_folio,
-	.launder_folio	= netfs_launder_folio,
 	.release_folio	= netfs_release_folio,
 	.invalidate_folio = netfs_invalidate_folio,
 	.migrate_folio	= filemap_migrate_folio,
@@ -354,7 +353,7 @@ static int afs_init_request(struct netfs_io_request *rreq, struct file *file)
 	if (file)
 		rreq->netfs_priv = key_get(afs_file_key(file));
 	rreq->rsize = 256 * 1024;
-	rreq->wsize = 256 * 1024;
+	rreq->wsize = 256 * 1024 * 1024;
 	return 0;
 }
 
@@ -369,6 +368,7 @@ static int afs_check_write_begin(struct file *file, loff_t pos, unsigned len,
 static void afs_free_request(struct netfs_io_request *rreq)
 {
 	key_put(rreq->netfs_priv);
+	afs_put_wb_key(rreq->netfs_priv2);
 }
 
 static void afs_update_i_size(struct inode *inode, loff_t new_i_size)
@@ -400,7 +400,9 @@ const struct netfs_request_ops afs_req_ops = {
 	.issue_read		= afs_issue_read,
 	.update_i_size		= afs_update_i_size,
 	.invalidate_cache	= afs_netfs_invalidate_cache,
-	.create_write_requests	= afs_create_write_requests,
+	.begin_writeback	= afs_begin_writeback,
+	.prepare_write		= afs_prepare_write,
+	.issue_write		= afs_issue_write,
 };
 
 static void afs_add_open_mmap(struct afs_vnode *vnode)

fs/afs/internal.h

@@ -916,7 +916,6 @@ struct afs_operation {
 			loff_t	pos;
 			loff_t	size;
 			loff_t	i_size;
-			bool	laundering;	/* Laundering page, PG_writeback not set */
 		} store;
 		struct {
 			struct iattr	*attr;
@@ -1599,11 +1598,14 @@ extern int afs_check_volume_status(struct afs_volume *, struct afs_operation *);
 /*
  * write.c
  */
+void afs_prepare_write(struct netfs_io_subrequest *subreq);
+void afs_issue_write(struct netfs_io_subrequest *subreq);
+void afs_begin_writeback(struct netfs_io_request *wreq);
+void afs_retry_request(struct netfs_io_request *wreq, struct netfs_io_stream *stream);
 extern int afs_writepages(struct address_space *, struct writeback_control *);
 extern int afs_fsync(struct file *, loff_t, loff_t, int);
 extern vm_fault_t afs_page_mkwrite(struct vm_fault *vmf);
 extern void afs_prune_wb_keys(struct afs_vnode *);
-void afs_create_write_requests(struct netfs_io_request *wreq, loff_t start, size_t len);
 
 /*
  * xattr.c

fs/afs/validation.c

@@ -365,9 +365,9 @@ static void afs_zap_data(struct afs_vnode *vnode)
 	 * written back in a regular file and completely discard the pages in a
 	 * directory or symlink */
 	if (S_ISREG(vnode->netfs.inode.i_mode))
-		invalidate_remote_inode(&vnode->netfs.inode);
+		filemap_invalidate_inode(&vnode->netfs.inode, true, 0, LLONG_MAX);
 	else
-		invalidate_inode_pages2(vnode->netfs.inode.i_mapping);
+		filemap_invalidate_inode(&vnode->netfs.inode, false, 0, LLONG_MAX);
 }
 
 /*