Btrfs: avoid tree log commit when there are no changes

rpm has a habit of running fdatasync when the file hasn't
changed.  We already detect if a file hasn't been changed
in the current transaction but it might have been sent to
the tree-log in this transaction and not changed since
the last call to fsync.

In this case, we want to avoid a tree log sync, which includes
a number of synchronous writes and barriers.  This commit
extends the existing tracking of the last transaction to change
a file to also track the last sub-transaction.

The end result is that rpm -ivh and -Uvh are roughly twice as fast,
and on par with ext3.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

8 files changed, 71 insertions, 16 deletions

diff --git a/fs/btrfs/btrfs_inode.h b/fs/btrfs/btrfs_inode.h
index c71abec0ab90..f6783a42f010 100644
--- a/fs/btrfs/btrfs_inode.h
+++ b/fs/btrfs/btrfs_inode.h
@@ -86,6 +86,12 @@ struct btrfs_inode {
          * transid of the trans_handle that last modified this inode
          */
         u64 last_trans;
+
+        /*
+         * log transid when this inode was last modified
+         */
+        u64 last_sub_trans;
+
         /*
          * transid that last logged this inode
          */
diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 36a19cd43e03..d0cede5ff25e 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1009,6 +1009,7 @@ struct btrfs_root {
         atomic_t log_writers;
         atomic_t log_commit[2];
         unsigned long log_transid;
+        unsigned long last_log_commit;
         unsigned long log_batch;
         pid_t log_start_pid;
         bool log_multiple_pids;
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index ac8927bdc33d..d4132aad9ea1 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -919,6 +919,7 @@ static int __setup_root(u32 nodesize, u32 leafsize, u32 sectorsize,
         atomic_set(&root->log_writers, 0);
         root->log_batch = 0;
         root->log_transid = 0;
+        root->last_log_commit = 0;
         extent_io_tree_init(&root->dirty_log_pages,
                              fs_info->btree_inode->i_mapping, GFP_NOFS);
 
@@ -1089,6 +1090,7 @@ int btrfs_add_log_tree(struct btrfs_trans_handle *trans,
         WARN_ON(root->log_root);
         root->log_root = log_root;
         root->log_transid = 0;
+        root->last_log_commit = 0;
         return 0;
 }
 
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 53fb1c997f0e..4599113ed72e 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1087,8 +1087,10 @@ out_nolock:
                                         btrfs_end_transaction(trans, root);
                                 else
                                         btrfs_commit_transaction(trans, root);
-                        } else {
+                        } else if (ret != BTRFS_NO_LOG_SYNC) {
                                 btrfs_commit_transaction(trans, root);
+                        } else {
+                                btrfs_end_transaction(trans, root);
                         }
                 }
                 if (file->f_flags & O_DIRECT) {
@@ -1138,6 +1140,13 @@ int btrfs_sync_file(struct file *file, struct dentry *dentry, int datasync)
         int ret = 0;
         struct btrfs_trans_handle *trans;
 
+
+        /* we wait first, since the writeback may change the inode */
+        root->log_batch++;
+        /* the VFS called filemap_fdatawrite for us */
+        btrfs_wait_ordered_range(inode, 0, (u64)-1);
+        root->log_batch++;
+
         /*
          * check the transaction that last modified this inode
          * and see if its already been committed
@@ -1145,6 +1154,11 @@ int btrfs_sync_file(struct file *file, struct dentry *dentry, int datasync)
         if (!BTRFS_I(inode)->last_trans)
                 goto out;
 
+        /*
+         * if the last transaction that changed this file was before
+         * the current transaction, we can bail out now without any
+         * syncing
+         */
         mutex_lock(&root->fs_info->trans_mutex);
         if (BTRFS_I(inode)->last_trans <=
             root->fs_info->last_trans_committed) {
@@ -1154,13 +1168,6 @@ int btrfs_sync_file(struct file *file, struct dentry *dentry, int datasync)
         }
         mutex_unlock(&root->fs_info->trans_mutex);
 
-        root->log_batch++;
-        filemap_fdatawrite(inode->i_mapping);
-        btrfs_wait_ordered_range(inode, 0, (u64)-1);
-        root->log_batch++;
-
-        if (datasync && !(inode->i_state & I_DIRTY_PAGES))
-                goto out;
         /*
          * ok we haven't committed the transaction yet, lets do a commit
          */
@@ -1189,14 +1196,18 @@ int btrfs_sync_file(struct file *file, struct dentry *dentry, int datasync)
          */
         mutex_unlock(&dentry->d_inode->i_mutex);
 
-        if (ret > 0) {
-                ret = btrfs_commit_transaction(trans, root);
-        } else {
-                ret = btrfs_sync_log(trans, root);
-                if (ret == 0)
-                        ret = btrfs_end_transaction(trans, root);
-                else
+        if (ret != BTRFS_NO_LOG_SYNC) {
+                if (ret > 0) {
                         ret = btrfs_commit_transaction(trans, root);
+                } else {
+                        ret = btrfs_sync_log(trans, root);
+                        if (ret == 0)
+                                ret = btrfs_end_transaction(trans, root);
+                        else
+                                ret = btrfs_commit_transaction(trans, root);
+                }
+        } else {
+                ret = btrfs_end_transaction(trans, root);
         }
         mutex_lock(&dentry->d_inode->i_mutex);
 out:
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index ef399a7794ff..5b9567caba0a 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -3480,6 +3480,7 @@ static noinline void init_btrfs_i(struct inode *inode)
         bi->generation = 0;
         bi->sequence = 0;
         bi->last_trans = 0;
+        bi->last_sub_trans = 0;
         bi->logged_trans = 0;
         bi->delalloc_bytes = 0;
         bi->reserved_bytes = 0;
@@ -4980,7 +4981,9 @@ again:
         set_page_dirty(page);
         SetPageUptodate(page);
 
-        BTRFS_I(inode)->last_trans = root->fs_info->generation + 1;
+        BTRFS_I(inode)->last_trans = root->fs_info->generation;
+        BTRFS_I(inode)->last_sub_trans = BTRFS_I(inode)->root->log_transid;
+
         unlock_extent(io_tree, page_start, page_end, GFP_NOFS);
 
 out_unlock:
@@ -5100,6 +5103,7 @@ struct inode *btrfs_alloc_inode(struct super_block *sb)
         if (!ei)
                 return NULL;
         ei->last_trans = 0;
+        ei->last_sub_trans = 0;
         ei->logged_trans = 0;
         ei->outstanding_extents = 0;
         ei->reserved_extents = 0;
diff --git a/fs/btrfs/transaction.h b/fs/btrfs/transaction.h
index 663c67404918..f68cbbe61e56 100644
--- a/fs/btrfs/transaction.h
+++ b/fs/btrfs/transaction.h
@@ -79,6 +79,7 @@ static inline void btrfs_set_inode_last_trans(struct btrfs_trans_handle *trans,
                                               struct inode *inode)
 {
         BTRFS_I(inode)->last_trans = trans->transaction->transid;
+        BTRFS_I(inode)->last_sub_trans = BTRFS_I(inode)->root->log_transid;
 }
 
 int btrfs_end_transaction(struct btrfs_trans_handle *trans,
diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index 6d9ec285644d..0a1bde268963 100644
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -1980,6 +1980,7 @@ int btrfs_sync_log(struct btrfs_trans_handle *trans,
         int ret;
         struct btrfs_root *log = root->log_root;
         struct btrfs_root *log_root_tree = root->fs_info->log_root_tree;
+        u64 log_transid = 0;
 
         mutex_lock(&root->log_mutex);
         index1 = root->log_transid % 2;
@@ -2018,6 +2019,7 @@ int btrfs_sync_log(struct btrfs_trans_handle *trans,
         btrfs_set_root_node(&log->root_item, log->node);
 
         root->log_batch = 0;
+        log_transid = root->log_transid;
         root->log_transid++;
         log->log_transid = root->log_transid;
         root->log_start_pid = 0;
@@ -2095,6 +2097,11 @@ int btrfs_sync_log(struct btrfs_trans_handle *trans,
         write_ctree_super(trans, root->fs_info->tree_root, 1);
         ret = 0;
 
+        mutex_lock(&root->log_mutex);
+        if (root->last_log_commit < log_transid)
+                root->last_log_commit = log_transid;
+        mutex_unlock(&root->log_mutex);
+
 out_wake_log_root:
         atomic_set(&log_root_tree->log_commit[index2], 0);
         smp_mb();
@@ -2862,6 +2869,21 @@ out:
         return ret;
 }
 
+static int inode_in_log(struct btrfs_trans_handle *trans,
+                 struct inode *inode)
+{
+        struct btrfs_root *root = BTRFS_I(inode)->root;
+        int ret = 0;
+
+        mutex_lock(&root->log_mutex);
+        if (BTRFS_I(inode)->logged_trans == trans->transid &&
+            BTRFS_I(inode)->last_sub_trans <= root->last_log_commit)
+                ret = 1;
+        mutex_unlock(&root->log_mutex);
+        return ret;
+}
+
+
 /*
  * helper function around btrfs_log_inode to make sure newly created
  * parent directories also end up in the log.  A minimal inode and backref
@@ -2901,6 +2923,11 @@ int btrfs_log_inode_parent(struct btrfs_trans_handle *trans,
         if (ret)
                 goto end_no_trans;
 
+        if (inode_in_log(trans, inode)) {
+                ret = BTRFS_NO_LOG_SYNC;
+                goto end_no_trans;
+        }
+
         start_log_trans(trans, root);
 
         ret = btrfs_log_inode(trans, root, inode, inode_only);
diff --git a/fs/btrfs/tree-log.h b/fs/btrfs/tree-log.h
index d09c7609e16b..0776eacb5083 100644
--- a/fs/btrfs/tree-log.h
+++ b/fs/btrfs/tree-log.h
@@ -19,6 +19,9 @@
 #ifndef __TREE_LOG_
 #define __TREE_LOG_
 
+/* return value for btrfs_log_dentry_safe that means we don't need to log it at all */
+#define BTRFS_NO_LOG_SYNC 256
+
 int btrfs_sync_log(struct btrfs_trans_handle *trans,
                    struct btrfs_root *root);
 int btrfs_free_log(struct btrfs_trans_handle *trans, struct btrfs_root *root);