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

diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index bd91987..e585657 100644 (file)
--- 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 e373f14..b40f6d5 100644 (file)
--- 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;
 }