identify multipage ->writepages() calls

 NFS needs to be able to distinguish between single-page ->writepage() calls and
 multipage ->writepages() calls.

 For the single-page writepage calls NFS can kick off the I/O within the
 context of ->writepage().

 For multipage ->writepages calls, nfs_writepage() will leave the I/O pending
 and nfs_writepages() will kick off the I/O when it all has been queued up
 within NFS.

 Cc: Trond Myklebust <trond.myklebust@fys.uio.no>
 Signed-off-by: Andrew Morton <akpm@osdl.org>
 Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

2 files changed, 13 insertions, 6 deletions

diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 64a36ba43b2f..b096159086e8 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -53,10 +53,11 @@ struct writeback_control {
         loff_t start;
         loff_t end;
 
-        unsigned nonblocking:1;                 /* Don't get stuck on request queues */
-        unsigned encountered_congestion:1;      /* An output: a queue is full */
-        unsigned for_kupdate:1;                 /* A kupdate writeback */
-        unsigned for_reclaim:1;                 /* Invoked from the page allocator */
+        unsigned nonblocking:1;         /* Don't get stuck on request queues */
+        unsigned encountered_congestion:1; /* An output: a queue is full */
+        unsigned for_kupdate:1;         /* A kupdate writeback */
+        unsigned for_reclaim:1;         /* Invoked from the page allocator */
+        unsigned for_writepages:1;      /* This is a writepages() call */
 };
 
 /*
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 0166ea15c9ee..5240e426c1f7 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -550,11 +550,17 @@ void __init page_writeback_init(void)
 
 int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
 {
+        int ret;
+
         if (wbc->nr_to_write <= 0)
                 return 0;
+        wbc->for_writepages = 1;
         if (mapping->a_ops->writepages)
-                return mapping->a_ops->writepages(mapping, wbc);
-        return generic_writepages(mapping, wbc);
+                ret =  mapping->a_ops->writepages(mapping, wbc);
+        else
+                ret = generic_writepages(mapping, wbc);
+        wbc->for_writepages = 0;
+        return ret;
 }
 
 /**