1 files changed, 17 insertions, 3 deletions

diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index b144b1957dd9..f55c437124a2 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -697,6 +697,17 @@ int nfs_flush_incompatible(struct file *file, struct page *page)
 }
 
 /*
+ * If the page cache is marked as unsafe or invalid, then we can't rely on
+ * the PageUptodate() flag. In this case, we will need to turn off
+ * write optimisations that depend on the page contents being correct.
+ */
+static int nfs_write_pageuptodate(struct page *page, struct inode *inode)
+{
+        return PageUptodate(page) &&
+                !(NFS_I(inode)->cache_validity & (NFS_INO_REVAL_PAGECACHE|NFS_INO_INVALID_DATA));
+}
+
+/*
  * Update and possibly write a cached page of an NFS file.
  *
  * XXX: Keep an eye on generic_file_read to make sure it doesn't do bad
@@ -717,10 +728,13 @@ int nfs_updatepage(struct file *file, struct page *page,
                 (long long)(page_offset(page) +offset));
 
         /* If we're not using byte range locks, and we know the page
-         * is entirely in cache, it may be more efficient to avoid
-         * fragmenting write requests.
+         * is up to date, it may be more efficient to extend the write
+         * to cover the entire page in order to avoid fragmentation
+         * inefficiencies.
          */
-        if (PageUptodate(page) && inode->i_flock == NULL && !(file->f_mode & O_SYNC)) {
+        if (nfs_write_pageuptodate(page, inode) &&
+                        inode->i_flock == NULL &&
+                        !(file->f_mode & O_SYNC)) {
                 count = max(count + offset, nfs_page_length(page));
                 offset = 0;
         }