2 files changed, 45 insertions, 15 deletions

diff --git a/fs/afs/write.c b/fs/afs/write.c
index e9ccaa3baf2e..3104b62c2082 100644
--- a/fs/afs/write.c
+++ b/fs/afs/write.c
@@ -118,6 +118,15 @@ int afs_write_end(struct file *file, struct address_space *mapping,
 	_enter("{%llx:%llu},{%lx}",
 	       vnode->fid.vid, vnode->fid.vnode, page->index);
 
+	if (!PageUptodate(page)) {
+		if (copied < len) {
+			copied = 0;
+			goto out;
+		}
+
+		SetPageUptodate(page);
+	}
+
 	if (copied == 0)
 		goto out;
 
@@ -132,8 +141,6 @@ int afs_write_end(struct file *file, struct address_space *mapping,
 		write_sequnlock(&vnode->cb_lock);
 	}
 
-	ASSERT(PageUptodate(page));
-
 	if (PagePrivate(page)) {
 		priv = page_private(page);
 		f = afs_page_dirty_from(page, priv);
diff --git a/fs/netfs/read_helper.c b/fs/netfs/read_helper.c
index 725614625ed4..0b6cd3b8734c 100644
--- a/fs/netfs/read_helper.c
+++ b/fs/netfs/read_helper.c
@@ -1011,12 +1011,42 @@ out:
 }
 EXPORT_SYMBOL(netfs_readpage);
 
-static void netfs_clear_thp(struct page *page)
+/**
+ * netfs_skip_page_read - prep a page for writing without reading first
+ * @page: page being prepared
+ * @pos: starting position for the write
+ * @len: length of write
+ *
+ * In some cases, write_begin doesn't need to read at all:
+ * - full page write
+ * - write that lies in a page that is completely beyond EOF
+ * - write that covers the the page from start to EOF or beyond it
+ *
+ * If any of these criteria are met, then zero out the unwritten parts
+ * of the page and return true. Otherwise, return false.
+ */
+static bool netfs_skip_page_read(struct page *page, loff_t pos, size_t len)
 {
-	unsigned int i;
+	struct inode *inode = page->mapping->host;
+	loff_t i_size = i_size_read(inode);
+	size_t offset = offset_in_thp(page, pos);
+
+	/* Full page write */
+	if (offset == 0 && len >= thp_size(page))
+		return true;
+
+	/* pos beyond last page in the file */
+	if (pos - offset >= i_size)
+		goto zero_out;
+
+	/* Write that covers from the start of the page to EOF or beyond */
+	if (offset == 0 && (pos + len) >= i_size)
+		goto zero_out;
 
-	for (i = 0; i < thp_nr_pages(page); i++)
-		clear_highpage(page + i);
+	return false;
+zero_out:
+	zero_user_segments(page, 0, offset, offset + len, thp_size(page));
+	return true;
 }
 
 /**
@@ -1024,7 +1054,7 @@ static void netfs_clear_thp(struct page *page)
  * @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
+ * @len: The length of the write (may extend beyond the end of the page chosen)
  * @flags: AOP_* flags
  * @_page: Where to put the resultant page
  * @_fsdata: Place for the netfs to store a cookie
@@ -1061,8 +1091,6 @@ int netfs_write_begin(struct file *file, struct address_space *mapping,
 	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;
 
 	DEFINE_READAHEAD(ractl, file, NULL, mapping, index);
@@ -1090,13 +1118,8 @@ retry:
 	 * 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_skip_page_read(page, pos, len)) {
 		netfs_stat(&netfs_n_rh_write_zskip);
 		goto have_page_no_wait;
 	}