2 files changed, 16 insertions, 3 deletions

diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index bd91987c065f..e585657e9831 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -63,6 +63,15 @@ struct writeback_control {
         unsigned for_writepages:1;      /* This is a writepages() call */
         unsigned range_cyclic:1;        /* range_start is cyclic */
         unsigned more_io:1;             /* more io to be dispatched */
+        /*
+         * write_cache_pages() won't update wbc->nr_to_write and
+         * mapping->writeback_index if no_nrwrite_index_update
+         * is set.  write_cache_pages() may write more than we
+         * requested and we want to make sure nr_to_write and
+         * writeback_index are updated in a consistent manner
+         * so we use a single control to update them
+         */
+        unsigned no_nrwrite_index_update:1;
 };
 
 /*
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index e373f14d26f6..b40f6d5f8fe9 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -876,6 +876,7 @@ int write_cache_pages(struct address_space *mapping,
         pgoff_t end;            /* Inclusive */
         int scanned = 0;
         int range_whole = 0;
+        long nr_to_write = wbc->nr_to_write;
 
         if (wbc->nonblocking && bdi_write_congested(bdi)) {
                 wbc->encountered_congestion = 1;
@@ -939,7 +940,7 @@ retry:
                                 unlock_page(page);
                                 ret = 0;
                         }
-                        if (ret || (--(wbc->nr_to_write) <= 0))
+                        if (ret || (--nr_to_write <= 0))
                                 done = 1;
                         if (wbc->nonblocking && bdi_write_congested(bdi)) {
                                 wbc->encountered_congestion = 1;
@@ -958,8 +959,11 @@ retry:
                 index = 0;
                 goto retry;
         }
-        if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
-                mapping->writeback_index = index;
+        if (!wbc->no_nrwrite_index_update) {
+                if (wbc->range_cyclic || (range_whole && nr_to_write > 0))
+                        mapping->writeback_index = index;
+                wbc->nr_to_write = nr_to_write;
+        }
 
         return ret;
 }