Btrfs: fix a bug in checking whether a inode is already in log

This is based on Josef's "Btrfs: turbo charge fsync".

The current btrfs checks if an inode is in log by comparing
root's last_log_commit to inode's last_sub_trans[2].

But the problem is that this root->last_log_commit is shared among
inodes.

Say we have N inodes to be logged, after the first inode,
root's last_log_commit is updated and the N-1 remained files will
be skipped.

This fixes the bug by keeping a local copy of root's last_log_commit
inside each inode and this local copy will be maintained itself.

[1]: we regard each log transaction as a subset of btrfs's transaction,
i.e. sub_trans

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>

4 files changed, 10 insertions, 8 deletions

diff --git a/fs/btrfs/btrfs_inode.h b/fs/btrfs/btrfs_inode.h
index 7c7bf818f3c1..ed8ca7ca5eff 100644
--- a/fs/btrfs/btrfs_inode.h
+++ b/fs/btrfs/btrfs_inode.h
@@ -144,6 +144,9 @@ struct btrfs_inode {
         /* flags field from the on disk inode */
         u32 flags;
 
+        /* a local copy of root's last_log_commit */
+        unsigned long last_log_commit;
+
         /*
          * Counters to keep track of the number of extent item's we may use due
          * to delalloc and such.  outstanding_extents is the number of extent
@@ -203,15 +206,10 @@ static inline bool btrfs_is_free_space_inode(struct inode *inode)
 
 static inline int btrfs_inode_in_log(struct inode *inode, u64 generation)
 {
-        struct btrfs_root *root = BTRFS_I(inode)->root;
-        int ret = 0;
-
-        mutex_lock(&root->log_mutex);
         if (BTRFS_I(inode)->logged_trans == generation &&
-            BTRFS_I(inode)->last_sub_trans <= root->last_log_commit)
-                ret = 1;
-        mutex_unlock(&root->log_mutex);
-        return ret;
+            BTRFS_I(inode)->last_sub_trans <= BTRFS_I(inode)->last_log_commit)
+                return 1;
+        return 0;
 }
 
 #endif
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index a6824bd04493..24745b8f2745 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -6774,6 +6774,7 @@ again:
 
         BTRFS_I(inode)->last_trans = root->fs_info->generation;
         BTRFS_I(inode)->last_sub_trans = BTRFS_I(inode)->root->log_transid;
+        BTRFS_I(inode)->last_log_commit = BTRFS_I(inode)->root->last_log_commit;
 
         unlock_extent_cached(io_tree, page_start, page_end, &cached_state, GFP_NOFS);
 
@@ -7018,6 +7019,7 @@ struct inode *btrfs_alloc_inode(struct super_block *sb)
         ei->csum_bytes = 0;
         ei->index_cnt = (u64)-1;
         ei->last_unlink_trans = 0;
+        ei->last_log_commit = 0;
 
         spin_lock_init(&ei->lock);
         ei->outstanding_extents = 0;
diff --git a/fs/btrfs/transaction.h b/fs/btrfs/transaction.h
index e8b8416c688b..1a138bfb8f13 100644
--- a/fs/btrfs/transaction.h
+++ b/fs/btrfs/transaction.h
@@ -88,6 +88,7 @@ static inline void btrfs_set_inode_last_trans(struct btrfs_trans_handle *trans,
 {
         BTRFS_I(inode)->last_trans = trans->transaction->transid;
         BTRFS_I(inode)->last_sub_trans = BTRFS_I(inode)->root->log_transid;
+        BTRFS_I(inode)->last_log_commit = BTRFS_I(inode)->root->last_log_commit;
 }
 
 int btrfs_end_transaction(struct btrfs_trans_handle *trans,
diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index 71e71539ffb7..fc0df95c2862 100644
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -3185,6 +3185,7 @@ next_slot:
                 }
         }
         BTRFS_I(inode)->logged_trans = trans->transid;
+        BTRFS_I(inode)->last_log_commit = BTRFS_I(inode)->last_sub_trans;
 out_unlock:
         mutex_unlock(&BTRFS_I(inode)->log_mutex);