vfs: Add no_nrwrite_index_update writeback control flag

If no_nrwrite_index_update is set we don't update nr_to_write and
address space writeback_index in write_cache_pages.  This change
enables a file system to skip these updates in write_cache_pages and do
them in the writepages() callback.  This patch will be followed by an
ext4 patch that make use of these new flags.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
CC: linux-fsdevel@vger.kernel.org

1 files changed, 7 insertions, 3 deletions

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;
 }