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From: David Howells <dhowells@redhat.com>
To: Trond Myklebust <trondmy@hammerspace.com>,
	Anna Schumaker <anna.schumaker@netapp.com>,
	Steve French <sfrench@samba.org>,
	Dominique Martinet <asmadeus@codewreck.org>
Cc: dhowells@redhat.com, Jeff Layton <jlayton@redhat.com>,
	David Wysochanski <dwysocha@redhat.com>,
	Matthew Wilcox <willy@infradead.org>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	linux-cachefs@redhat.com, linux-afs@lists.infradead.org,
	linux-nfs@vger.kernel.org, linux-cifs@vger.kernel.org,
	ceph-devel@vger.kernel.org, v9fs-developer@lists.sourceforge.net,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH 09/32] netfs: Add write_begin helper
Date: Mon, 25 Jan 2021 21:32:35 +0000	[thread overview]
Message-ID: <161161035539.2537118.15674887534950908530.stgit@warthog.procyon.org.uk> (raw)
In-Reply-To: <161161025063.2537118.2009249444682241405.stgit@warthog.procyon.org.uk>

Add a helper to do the pre-reading work for the netfs write_begin address
space op.

Signed-off-by: David Howells <dhowells@redhat.com>
---

 fs/netfs/internal.h          |    2 +
 fs/netfs/read_helper.c       |  165 ++++++++++++++++++++++++++++++++++++++++++
 fs/netfs/stats.c             |   10 ++-
 include/linux/netfs.h        |    8 ++
 include/trace/events/netfs.h |    4 +
 5 files changed, 185 insertions(+), 4 deletions(-)

diff --git a/fs/netfs/internal.h b/fs/netfs/internal.h
index 98b6f4516da1..b7f2c4459f33 100644
--- a/fs/netfs/internal.h
+++ b/fs/netfs/internal.h
@@ -34,8 +34,10 @@ extern atomic_t netfs_n_rh_read_failed;
 extern atomic_t netfs_n_rh_zero;
 extern atomic_t netfs_n_rh_short_read;
 extern atomic_t netfs_n_rh_write;
+extern atomic_t netfs_n_rh_write_begin;
 extern atomic_t netfs_n_rh_write_done;
 extern atomic_t netfs_n_rh_write_failed;
+extern atomic_t netfs_n_rh_write_zskip;
 
 
 static inline void netfs_stat(atomic_t *stat)
diff --git a/fs/netfs/read_helper.c b/fs/netfs/read_helper.c
index 275ac37e2834..eb34c368617d 100644
--- a/fs/netfs/read_helper.c
+++ b/fs/netfs/read_helper.c
@@ -760,3 +760,168 @@ int netfs_readpage(struct file *file,
 	return ret;
 }
 EXPORT_SYMBOL(netfs_readpage);
+
+static void netfs_clear_thp(struct page *page)
+{
+	unsigned int i;
+
+	for (i = 0; i < thp_nr_pages(page); i++)
+		clear_highpage(page + i);
+}
+
+/**
+ * netfs_write_begin - Helper to prepare for writing
+ * @file: The file to read from
+ * @mapping: The mapping to read from
+ * @pos: File position at which the write will begin
+ * @len: The length of the write in this page
+ * @flags: AOP_* flags
+ * @_page: Where to put the resultant page
+ * @_fsdata: Place for the netfs to store a cookie
+ * @ops: The network filesystem's operations for the helper to use
+ * @netfs_priv: Private netfs data to be retained in the request
+ *
+ * Pre-read data for a write-begin request by drawing data from the cache if
+ * possible, or the netfs if not.  Space beyond the EOF is zero-filled.
+ * Multiple I/O requests from different sources will get munged together.  If
+ * necessary, the readahead window can be expanded in either direction to a
+ * more convenient alighment for RPC efficiency or to make storage in the cache
+ * feasible.
+ *
+ * The calling netfs must provide a table of operations, only one of which,
+ * issue_op, is mandatory.
+ *
+ * The check_write_begin() operation can be provided to check for and flush
+ * conflicting writes once the page is grabbed and locked.  It is passed a
+ * pointer to the fsdata cookie that gets returned to the VM to be passed to
+ * write_end.  It is permitted to sleep.  It should return 0 if the request
+ * should go ahead; unlock the page and return -EAGAIN to cause the page to be
+ * regot; or return an error.
+ *
+ * This is usable whether or not caching is enabled.
+ */
+int netfs_write_begin(struct file *file, struct address_space *mapping,
+		      loff_t pos, unsigned int len, unsigned int flags,
+		      struct page **_page, void **_fsdata,
+		      const struct netfs_read_request_ops *ops,
+		      void *netfs_priv)
+{
+	struct netfs_read_request *rreq;
+	struct page *page, *xpage;
+	struct inode *inode = file_inode(file);
+	unsigned int debug_index = 0;
+	pgoff_t index = pos >> PAGE_SHIFT;
+	int pos_in_page = pos & ~PAGE_MASK;
+	loff_t size;
+	int ret;
+
+	struct readahead_control ractl = {
+		.file		= file,
+		.mapping	= mapping,
+		._index		= index,
+		._nr_pages	= 0,
+	};
+
+retry:
+	page = grab_cache_page_write_begin(mapping, index, 0);
+	if (!page)
+		return -ENOMEM;
+
+	if (ops->check_write_begin) {
+		/* Allow the netfs (eg. ceph) to flush conflicts. */
+		ret = ops->check_write_begin(file, pos, len, page, _fsdata);
+		if (ret < 0) {
+			if (ret == -EAGAIN)
+				goto retry;
+			goto error;
+		}
+	}
+
+	if (PageUptodate(page))
+		goto have_page;
+
+	/* If the page is beyond the EOF, we want to clear it - unless it's
+	 * within the cache granule containing the EOF, in which case we need
+	 * to preload the granule.
+	 */
+	size = i_size_read(inode);
+	if (!ops->is_cache_enabled(inode) &&
+	    ((pos_in_page == 0 && len == thp_size(page)) ||
+	     (pos >= size) ||
+	     (pos_in_page == 0 && (pos + len) >= size))) {
+		netfs_clear_thp(page);
+		SetPageUptodate(page);
+		netfs_stat(&netfs_n_rh_write_zskip);
+		goto have_page_no_wait;
+	}
+
+	ret = -ENOMEM;
+	rreq = netfs_alloc_read_request(ops, netfs_priv, file);
+	if (!rreq)
+		goto error;
+	rreq->mapping		= page->mapping;
+	rreq->start		= page->index * PAGE_SIZE;
+	rreq->len		= thp_size(page);
+	rreq->no_unlock_page	= page->index;
+	__set_bit(NETFS_RREQ_NO_UNLOCK_PAGE, &rreq->flags);
+	netfs_priv = NULL;
+
+	netfs_stat(&netfs_n_rh_write_begin);
+	trace_netfs_read(rreq, pos, len, netfs_read_trace_write_begin);
+
+	/* Expand the request to meet caching requirements and download
+	 * preferences.
+	 */
+	ractl._nr_pages = thp_nr_pages(page);
+	netfs_rreq_expand(rreq, &ractl);
+	netfs_get_read_request(rreq);
+
+	/* We hold the page locks, so we can drop the references */
+	while ((xpage = readahead_page(&ractl)))
+		if (xpage != page)
+			put_page(xpage);
+
+	atomic_set(&rreq->nr_rd_ops, 1);
+	do {
+		if (!netfs_rreq_submit_slice(rreq, &debug_index))
+			break;
+
+	} while (rreq->submitted < rreq->len);
+
+	// TODO: If we didn't submit enough readage, we need to clean up
+
+	/* Keep nr_rd_ops incremented so that the ref always belongs to us, and
+	 * the service code isn't punted off to a random thread pool to
+	 * process.
+	 */
+	for (;;) {
+		wait_var_event(&rreq->nr_rd_ops, atomic_read(&rreq->nr_rd_ops) == 1);
+		netfs_rreq_assess(rreq);
+		if (!test_bit(NETFS_RREQ_IN_PROGRESS, &rreq->flags))
+			break;
+		cond_resched();
+	}
+
+	ret = rreq->error;
+	netfs_put_read_request(rreq);
+	if (ret < 0)
+		goto error;
+
+have_page:
+	wait_on_page_fscache(page);
+have_page_no_wait:
+	if (netfs_priv)
+		ops->cleanup(netfs_priv, mapping);
+	*_page = page;
+	_leave(" = 0");
+	return 0;
+
+error:
+	unlock_page(page);
+	put_page(page);
+	if (netfs_priv)
+		ops->cleanup(netfs_priv, mapping);
+	_leave(" = %d", ret);
+	return ret;
+}
+EXPORT_SYMBOL(netfs_write_begin);
diff --git a/fs/netfs/stats.c b/fs/netfs/stats.c
index df6ff5718f25..dd7ad66ed07e 100644
--- a/fs/netfs/stats.c
+++ b/fs/netfs/stats.c
@@ -24,19 +24,23 @@ atomic_t netfs_n_rh_read_failed;
 atomic_t netfs_n_rh_zero;
 atomic_t netfs_n_rh_short_read;
 atomic_t netfs_n_rh_write;
+atomic_t netfs_n_rh_write_begin;
 atomic_t netfs_n_rh_write_done;
 atomic_t netfs_n_rh_write_failed;
+atomic_t netfs_n_rh_write_zskip;
 
 void netfs_stats_show(struct seq_file *m)
 {
-	seq_printf(m, "RdHelp : RA=%u RP=%u rr=%u sr=%u\n",
+	seq_printf(m, "RdHelp : RA=%u RP=%u WB=%u rr=%u sr=%u\n",
 		   atomic_read(&netfs_n_rh_readahead),
 		   atomic_read(&netfs_n_rh_readpage),
+		   atomic_read(&netfs_n_rh_write_begin),
 		   atomic_read(&netfs_n_rh_rreq),
 		   atomic_read(&netfs_n_rh_sreq));
-	seq_printf(m, "RdHelp : ZR=%u sh=%u\n",
+	seq_printf(m, "RdHelp : ZR=%u sh=%u sk=%u\n",
 		   atomic_read(&netfs_n_rh_zero),
-		   atomic_read(&netfs_n_rh_short_read));
+		   atomic_read(&netfs_n_rh_short_read),
+		   atomic_read(&netfs_n_rh_write_zskip));
 	seq_printf(m, "RdHelp : DL=%u ds=%u df=%u di=%u\n",
 		   atomic_read(&netfs_n_rh_download),
 		   atomic_read(&netfs_n_rh_download_done),
diff --git a/include/linux/netfs.h b/include/linux/netfs.h
index 92a08d8b8e61..5b54f6637c22 100644
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -87,11 +87,14 @@ struct netfs_read_request {
  * Operations the network filesystem can/must provide to the helpers.
  */
 struct netfs_read_request_ops {
+	bool (*is_cache_enabled)(struct inode *inode);
 	void (*init_rreq)(struct netfs_read_request *rreq, struct file *file);
 	void (*expand_readahead)(struct netfs_read_request *rreq);
 	bool (*clamp_length)(struct netfs_read_subrequest *subreq);
 	void (*issue_op)(struct netfs_read_subrequest *subreq);
 	bool (*is_still_valid)(struct netfs_read_request *rreq);
+	int (*check_write_begin)(struct file *file, loff_t pos, unsigned len,
+				 struct page *page, void **_fsdata);
 	void (*done)(struct netfs_read_request *rreq);
 	void (*cleanup)(struct address_space *mapping, void *netfs_priv);
 };
@@ -104,6 +107,11 @@ extern int netfs_readpage(struct file *,
 			  struct page *,
 			  const struct netfs_read_request_ops *,
 			  void *);
+extern int netfs_write_begin(struct file *, struct address_space *,
+			     loff_t, unsigned int, unsigned int, struct page **,
+			     void **,
+			     const struct netfs_read_request_ops *,
+			     void *);
 
 extern void netfs_subreq_terminated(struct netfs_read_subrequest *, ssize_t);
 extern void netfs_stats_show(struct seq_file *);
diff --git a/include/trace/events/netfs.h b/include/trace/events/netfs.h
index 12ad382764c5..a2bf6cd84bd4 100644
--- a/include/trace/events/netfs.h
+++ b/include/trace/events/netfs.h
@@ -22,6 +22,7 @@ enum netfs_read_trace {
 	netfs_read_trace_expanded,
 	netfs_read_trace_readahead,
 	netfs_read_trace_readpage,
+	netfs_read_trace_write_begin,
 };
 
 enum netfs_rreq_trace {
@@ -50,7 +51,8 @@ enum netfs_sreq_trace {
 #define netfs_read_traces					\
 	EM(netfs_read_trace_expanded,		"EXPANDED ")	\
 	EM(netfs_read_trace_readahead,		"READAHEAD")	\
-	E_(netfs_read_trace_readpage,		"READPAGE ")
+	EM(netfs_read_trace_readpage,		"READPAGE ")	\
+	E_(netfs_read_trace_write_begin,	"WRITEBEGN")
 
 #define netfs_rreq_traces					\
 	EM(netfs_rreq_trace_assess,		"ASSESS")	\



  parent reply	other threads:[~2021-01-25 22:51 UTC|newest]

Thread overview: 41+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-25 21:30 [PATCH 00/32] Network fs helper library & fscache kiocb API [ver #2] David Howells
2021-01-25 21:31 ` [PATCH 01/32] iov_iter: Add ITER_XARRAY David Howells
2021-01-25 21:31 ` [PATCH 02/32] vm: Add wait/unlock functions for PG_fscache David Howells
2021-01-25 21:31 ` [PATCH 03/32] mm: Implement readahead_control pageset expansion David Howells
2021-01-25 21:31 ` [PATCH 04/32] vfs: Export rw_verify_area() for use by cachefiles David Howells
2021-01-25 21:31 ` [PATCH 05/32] netfs: Make a netfs helper module David Howells
2021-01-25 21:32 ` [PATCH 06/32] netfs: Provide readahead and readpage netfs helpers David Howells
2021-01-25 21:32 ` [PATCH 07/32] netfs: Add tracepoints David Howells
2021-01-25 21:32 ` [PATCH 08/32] netfs: Gather stats David Howells
2021-01-25 21:32 ` David Howells [this message]
2021-01-25 21:32 ` [PATCH 10/32] netfs: Define an interface to talk to a cache David Howells
2021-01-25 21:32 ` [PATCH 11/32] fscache, cachefiles: Add alternate API to use kiocb for read/write to cache David Howells
2021-01-25 21:33 ` [PATCH 12/32] afs: Disable use of the fscache I/O routines David Howells
2021-01-25 21:33 ` [PATCH 13/32] afs: Pass page into dirty region helpers to provide THP size David Howells
2021-01-25 21:33 ` [PATCH 14/32] afs: Print the operation debug_id when logging an unexpected data version David Howells
2021-01-25 21:33 ` [PATCH 15/32] afs: Move key to afs_read struct David Howells
2021-01-25 21:34 ` [PATCH 16/32] afs: Don't truncate iter during data fetch David Howells
2021-01-25 21:34 ` [PATCH 17/32] afs: Log remote unmarshalling errors David Howells
2021-01-25 21:34 ` [PATCH 18/32] afs: Set up the iov_iter before calling afs_extract_data() David Howells
2021-01-25 21:34 ` [PATCH 19/32] afs: Use ITER_XARRAY for writing David Howells
2021-01-25 21:34 ` [PATCH 20/32] afs: Wait on PG_fscache before modifying/releasing a page David Howells
2021-01-25 21:35 ` [PATCH 21/32] afs: Extract writeback extension into its own function David Howells
2021-01-25 21:35 ` [PATCH 22/32] afs: Prepare for use of THPs David Howells
2021-01-25 21:35 ` [PATCH 23/32] afs: Use the fs operation ops to handle FetchData completion David Howells
2021-01-25 21:35 ` [PATCH 24/32] afs: Use new fscache read helper API David Howells
2021-01-25 21:35 ` [PATCH 25/32] NFS: Clean up nfs_readpage() and nfs_readpages() David Howells
2021-01-26  3:59   ` Matthew Wilcox
2021-01-26 15:33     ` David Wysochanski
2021-01-25 21:36 ` [PATCH 26/32] NFS: In nfs_readpage() only increment NFSIOS_READPAGES when read succeeds David Howells
2021-01-25 21:36 ` [PATCH 27/32] NFS: Refactor nfs_readpage() and nfs_readpage_async() to use nfs_readdesc David Howells
2021-01-26  4:05   ` Matthew Wilcox
2021-01-26 15:24     ` David Wysochanski
2021-01-25 21:36 ` [PATCH 28/32] NFS: Call readpage_async_filler() from nfs_readpage_async() David Howells
2021-01-25 21:36 ` [PATCH 29/32] NFS: Add nfs_pageio_complete_read() and remove nfs_readpage_async() David Howells
2021-01-25 21:37 ` [PATCH 30/32] NFS: Allow internal use of read structs and functions David Howells
2021-01-25 21:37 ` [PATCH 31/32] NFS: Convert to the netfs API and nfs_readpage to use netfs_readpage David Howells
2021-01-25 21:37 ` [PATCH 32/32] NFS: Convert readpage to readahead and use netfs_readahead for fscache David Howells
2021-01-26  1:36   ` Matthew Wilcox
2021-01-26 15:24     ` Chuck Lever
2021-01-26 19:10       ` David Wysochanski
2021-01-26 18:25     ` David Wysochanski

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