ext4: add optimization for the lazytime mount option

Add an optimization for the MS_LAZYTIME mount option so that we will
opportunistically write out any inodes with the I_DIRTY_TIME flag set
in a particular inode table block when we need to update some inode in
that inode table block anyway.

Also add some temporary code so that we can set the lazytime mount
option without needing a modified /sbin/mount program which can set
MS_LAZYTIME.  We can eventually make this go away once util-linux has
added support.

Google-Bug-Id: 18297052

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 10 insertions, 0 deletions

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 74c5f53595fb..362b23c8497a 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -1139,6 +1139,7 @@ enum {
         Opt_noquota, Opt_barrier, Opt_nobarrier, Opt_err,
         Opt_usrquota, Opt_grpquota, Opt_i_version,
         Opt_stripe, Opt_delalloc, Opt_nodelalloc, Opt_mblk_io_submit,
+        Opt_lazytime, Opt_nolazytime,
         Opt_nomblk_io_submit, Opt_block_validity, Opt_noblock_validity,
         Opt_inode_readahead_blks, Opt_journal_ioprio,
         Opt_dioread_nolock, Opt_dioread_lock,
@@ -1202,6 +1203,8 @@ static const match_table_t tokens = {
         {Opt_i_version, "i_version"},
         {Opt_stripe, "stripe=%u"},
         {Opt_delalloc, "delalloc"},
+        {Opt_lazytime, "lazytime"},
+        {Opt_nolazytime, "nolazytime"},
         {Opt_nodelalloc, "nodelalloc"},
         {Opt_removed, "mblk_io_submit"},
         {Opt_removed, "nomblk_io_submit"},
@@ -1459,6 +1462,12 @@ static int handle_mount_opt(struct super_block *sb, char *opt, int token,
         case Opt_i_version:
                 sb->s_flags |= MS_I_VERSION;
                 return 1;
+        case Opt_lazytime:
+                sb->s_flags |= MS_LAZYTIME;
+                return 1;
+        case Opt_nolazytime:
+                sb->s_flags &= ~MS_LAZYTIME;
+                return 1;
         }
 
         for (m = ext4_mount_opts; m->token != Opt_err; m++)
@@ -5020,6 +5029,7 @@ static int ext4_remount(struct super_block *sb, int *flags, char *data)
         }
 #endif
 
+        *flags = (*flags & ~MS_LAZYTIME) | (sb->s_flags & MS_LAZYTIME);
         ext4_msg(sb, KERN_INFO, "re-mounted. Opts: %s", orig_data);
         kfree(orig_data);
         return 0;