NFS: Writeback optimisation

Schedule writes using WB_SYNC_NONE first, then come back for a second pass
using WB_SYNC_ALL.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index 75adb8e..b3c5f5d 100644 (file)
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -1325,21 +1325,14 @@ long nfs_sync_mapping_wait(struct address_space *mapping, struct writeback_contr
        return ret;
 }
 
-static int nfs_write_mapping(struct address_space *mapping, int how)
+static int __nfs_write_mapping(struct address_space *mapping, struct writeback_control *wbc, int how)
 {
-       struct writeback_control wbc = {
-               .bdi = mapping->backing_dev_info,
-               .sync_mode = WB_SYNC_ALL,
-               .nr_to_write = LONG_MAX,
-               .for_writepages = 1,
-               .range_cyclic = 1,
-       };
        int ret;
 
-       ret = nfs_writepages(mapping, &wbc);
+       ret = nfs_writepages(mapping, wbc);
        if (ret < 0)
                goto out;
-       ret = nfs_sync_mapping_wait(mapping, &wbc, how);
+       ret = nfs_sync_mapping_wait(mapping, wbc, how);
        if (ret < 0)
                goto out;
        return 0;
@@ -1348,6 +1341,25 @@ out:
        return ret;
 }
 
+/* Two pass sync: first using WB_SYNC_NONE, then WB_SYNC_ALL */
+static int nfs_write_mapping(struct address_space *mapping, int how)
+{
+       struct writeback_control wbc = {
+               .bdi = mapping->backing_dev_info,
+               .sync_mode = WB_SYNC_NONE,
+               .nr_to_write = LONG_MAX,
+               .for_writepages = 1,
+               .range_cyclic = 1,
+       };
+       int ret;
+
+       ret = __nfs_write_mapping(mapping, &wbc, how);
+       if (ret < 0)
+               return ret;
+       wbc.sync_mode = WB_SYNC_ALL;
+       return __nfs_write_mapping(mapping, &wbc, how);
+}
+
 /*
  * flush the inode to disk.
  */