Btrfs: avoid starting a transaction in the write path

I noticed while looking at a deadlock that we are always starting a transaction
in cow_file_range().  This isn't really needed since we only need a transaction
if we are doing an inline extent, or if the allocator needs to allocate a chunk.
So push down all the transaction start stuff to be closer to where we actually
need a transaction in all of these cases.  This will hopefully reduce our write
latency when we are committing often.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 063e485..7c93d9f 100644 (file)
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -3165,11 +3165,9 @@ int btrfs_alloc_logged_file_extent(struct btrfs_trans_handle *trans,
                                   struct btrfs_root *root,
                                   u64 root_objectid, u64 owner, u64 offset,
                                   struct btrfs_key *ins);
-int btrfs_reserve_extent(struct btrfs_trans_handle *trans,
-                                 struct btrfs_root *root,
-                                 u64 num_bytes, u64 min_alloc_size,
-                                 u64 empty_size, u64 hint_byte,
-                                 struct btrfs_key *ins, int is_data);
+int btrfs_reserve_extent(struct btrfs_root *root, u64 num_bytes,
+                        u64 min_alloc_size, u64 empty_size, u64 hint_byte,
+                        struct btrfs_key *ins, int is_data);
 int btrfs_inc_ref(struct btrfs_trans_handle *trans, struct btrfs_root *root,
                  struct extent_buffer *buf, int full_backref, int for_cow);
 int btrfs_dec_ref(struct btrfs_trans_handle *trans, struct btrfs_root *root,
@@ -3612,8 +3610,7 @@ void btrfs_wait_and_free_delalloc_work(struct btrfs_delalloc_work *work);
 struct extent_map *btrfs_get_extent_fiemap(struct inode *inode, struct page *page,
                                           size_t pg_offset, u64 start, u64 len,
                                           int create);
-noinline int can_nocow_extent(struct btrfs_trans_handle *trans,
-                             struct inode *inode, u64 offset, u64 *len,
+noinline int can_nocow_extent(struct inode *inode, u64 offset, u64 *len,
                              u64 *orig_start, u64 *orig_block_len,
                              u64 *ram_bytes);
 

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 277d2c2..f1c1694 100644 (file)
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -6121,8 +6121,7 @@ enum btrfs_loop_type {
  * ins->offset == number of blocks
  * Any available blocks before search_start are skipped.
  */
-static noinline int find_free_extent(struct btrfs_trans_handle *trans,
-                                    struct btrfs_root *orig_root,
+static noinline int find_free_extent(struct btrfs_root *orig_root,
                                     u64 num_bytes, u64 empty_size,
                                     u64 hint_byte, struct btrfs_key *ins,
                                     u64 flags)
@@ -6345,10 +6344,10 @@ refill_cluster:
                                              block_group->full_stripe_len);
 
                        /* allocate a cluster in this block group */
-                       ret = btrfs_find_space_cluster(trans, root,
-                                              block_group, last_ptr,
-                                              search_start, num_bytes,
-                                              aligned_cluster);
+                       ret = btrfs_find_space_cluster(root, block_group,
+                                                      last_ptr, search_start,
+                                                      num_bytes,
+                                                      aligned_cluster);
                        if (ret == 0) {
                                /*
                                 * now pull our allocation out of this
@@ -6479,17 +6478,28 @@ loop:
                index = 0;
                loop++;
                if (loop == LOOP_ALLOC_CHUNK) {
+                       struct btrfs_trans_handle *trans;
+
+                       trans = btrfs_join_transaction(root);
+                       if (IS_ERR(trans)) {
+                               ret = PTR_ERR(trans);
+                               goto out;
+                       }
+
                        ret = do_chunk_alloc(trans, root, flags,
                                             CHUNK_ALLOC_FORCE);
                        /*
                         * Do not bail out on ENOSPC since we
                         * can do more things.
                         */
-                       if (ret < 0 && ret != -ENOSPC) {
+                       if (ret < 0 && ret != -ENOSPC)
                                btrfs_abort_transaction(trans,
                                                        root, ret);
+                       else
+                               ret = 0;
+                       btrfs_end_transaction(trans, root);
+                       if (ret)
                                goto out;
-                       }
                }
 
                if (loop == LOOP_NO_EMPTY_SIZE) {
@@ -6553,8 +6563,7 @@ again:
        up_read(&info->groups_sem);
 }
 
-int btrfs_reserve_extent(struct btrfs_trans_handle *trans,
-                        struct btrfs_root *root,
+int btrfs_reserve_extent(struct btrfs_root *root,
                         u64 num_bytes, u64 min_alloc_size,
                         u64 empty_size, u64 hint_byte,
                         struct btrfs_key *ins, int is_data)
@@ -6566,8 +6575,8 @@ int btrfs_reserve_extent(struct btrfs_trans_handle *trans,
        flags = btrfs_get_alloc_profile(root, is_data);
 again:
        WARN_ON(num_bytes < root->sectorsize);
-       ret = find_free_extent(trans, root, num_bytes, empty_size,
-                              hint_byte, ins, flags);
+       ret = find_free_extent(root, num_bytes, empty_size, hint_byte, ins,
+                              flags);
 
        if (ret == -ENOSPC) {
                if (!final_tried) {
@@ -6955,7 +6964,7 @@ struct extent_buffer *btrfs_alloc_free_block(struct btrfs_trans_handle *trans,
        if (IS_ERR(block_rsv))
                return ERR_CAST(block_rsv);
 
-       ret = btrfs_reserve_extent(trans, root, blocksize, blocksize,
+       ret = btrfs_reserve_extent(root, blocksize, blocksize,
                                   empty_size, hint, &ins, 0);
        if (ret) {
                unuse_block_rsv(root->fs_info, block_rsv, blocksize);

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 8cc941e..5e7ea99 100644 (file)
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1339,7 +1339,6 @@ fail:
 static noinline int check_can_nocow(struct inode *inode, loff_t pos,
                                    size_t *write_bytes)
 {
-       struct btrfs_trans_handle *trans;
        struct btrfs_root *root = BTRFS_I(inode)->root;
        struct btrfs_ordered_extent *ordered;
        u64 lockstart, lockend;
@@ -1361,16 +1360,8 @@ static noinline int check_can_nocow(struct inode *inode, loff_t pos,
                btrfs_put_ordered_extent(ordered);
        }
 
-       trans = btrfs_join_transaction(root);
-       if (IS_ERR(trans)) {
-               unlock_extent(&BTRFS_I(inode)->io_tree, lockstart, lockend);
-               return PTR_ERR(trans);
-       }
-
        num_bytes = lockend - lockstart + 1;
-       ret = can_nocow_extent(trans, inode, lockstart, &num_bytes, NULL, NULL,
-                              NULL);
-       btrfs_end_transaction(trans, root);
+       ret = can_nocow_extent(inode, lockstart, &num_bytes, NULL, NULL, NULL);
        if (ret <= 0) {
                ret = 0;
        } else {

diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c
index b21a3cd..25f906f 100644 (file)
--- a/fs/btrfs/free-space-cache.c
+++ b/fs/btrfs/free-space-cache.c
@@ -2525,8 +2525,7 @@ setup_cluster_bitmap(struct btrfs_block_group_cache *block_group,
  * returns zero and sets up cluster if things worked out, otherwise
  * it returns -enospc
  */
-int btrfs_find_space_cluster(struct btrfs_trans_handle *trans,
-                            struct btrfs_root *root,
+int btrfs_find_space_cluster(struct btrfs_root *root,
                             struct btrfs_block_group_cache *block_group,
                             struct btrfs_free_cluster *cluster,
                             u64 offset, u64 bytes, u64 empty_size)

diff --git a/fs/btrfs/free-space-cache.h b/fs/btrfs/free-space-cache.h
index 894116b..4acfb19 100644 (file)
--- a/fs/btrfs/free-space-cache.h
+++ b/fs/btrfs/free-space-cache.h
@@ -98,8 +98,7 @@ u64 btrfs_find_space_for_alloc(struct btrfs_block_group_cache *block_group,
 u64 btrfs_find_ino_for_alloc(struct btrfs_root *fs_root);
 void btrfs_dump_free_space(struct btrfs_block_group_cache *block_group,
                           u64 bytes);
-int btrfs_find_space_cluster(struct btrfs_trans_handle *trans,
-                            struct btrfs_root *root,
+int btrfs_find_space_cluster(struct btrfs_root *root,
                             struct btrfs_block_group_cache *block_group,
                             struct btrfs_free_cluster *cluster,
                             u64 offset, u64 bytes, u64 empty_size);

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index de7085b..264feef 100644 (file)
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -230,12 +230,13 @@ fail:
  * does the checks required to make sure the data is small enough
  * to fit as an inline extent.
  */
-static noinline int cow_file_range_inline(struct btrfs_trans_handle *trans,
-                                struct btrfs_root *root,
-                                struct inode *inode, u64 start, u64 end,
-                                size_t compressed_size, int compress_type,
-                                struct page **compressed_pages)
+static noinline int cow_file_range_inline(struct btrfs_root *root,
+                                         struct inode *inode, u64 start,
+                                         u64 end, size_t compressed_size,
+                                         int compress_type,
+                                         struct page **compressed_pages)
 {
+       struct btrfs_trans_handle *trans;
        u64 isize = i_size_read(inode);
        u64 actual_end = min(end + 1, isize);
        u64 inline_len = actual_end - start;
@@ -256,9 +257,16 @@ static noinline int cow_file_range_inline(struct btrfs_trans_handle *trans,
                return 1;
        }
 
+       trans = btrfs_join_transaction(root);
+       if (IS_ERR(trans))
+               return PTR_ERR(trans);
+       trans->block_rsv = &root->fs_info->delalloc_block_rsv;
+
        ret = btrfs_drop_extents(trans, root, inode, start, aligned_end, 1);
-       if (ret)
-               return ret;
+       if (ret) {
+               btrfs_abort_transaction(trans, root, ret);
+               goto out;
+       }
 
        if (isize > actual_end)
                inline_len = min_t(u64, isize, actual_end);
@@ -267,15 +275,18 @@ static noinline int cow_file_range_inline(struct btrfs_trans_handle *trans,
                                   compress_type, compressed_pages);
        if (ret && ret != -ENOSPC) {
                btrfs_abort_transaction(trans, root, ret);
-               return ret;
+               goto out;
        } else if (ret == -ENOSPC) {
-               return 1;
+               ret = 1;
+               goto out;
        }
 
        set_bit(BTRFS_INODE_NEEDS_FULL_SYNC, &BTRFS_I(inode)->runtime_flags);
        btrfs_delalloc_release_metadata(inode, end + 1 - start);
        btrfs_drop_extent_cache(inode, start, aligned_end - 1, 0);
-       return 0;
+out:
+       btrfs_end_transaction(trans, root);
+       return ret;
 }
 
 struct async_extent {
@@ -343,7 +354,6 @@ static noinline int compress_file_range(struct inode *inode,
                                        int *num_added)
 {
        struct btrfs_root *root = BTRFS_I(inode)->root;
-       struct btrfs_trans_handle *trans;
        u64 num_bytes;
        u64 blocksize = root->sectorsize;
        u64 actual_end;
@@ -461,25 +471,16 @@ again:
        }
 cont:
        if (start == 0) {
-               trans = btrfs_join_transaction(root);
-               if (IS_ERR(trans)) {
-                       ret = PTR_ERR(trans);
-                       trans = NULL;
-                       goto cleanup_and_out;
-               }
-               trans->block_rsv = &root->fs_info->delalloc_block_rsv;
-
                /* lets try to make an inline extent */
                if (ret || total_in < (actual_end - start)) {
                        /* we didn't compress the entire range, try
                         * to make an uncompressed inline extent.
                         */
-                       ret = cow_file_range_inline(trans, root, inode,
-                                                   start, end, 0, 0, NULL);
+                       ret = cow_file_range_inline(root, inode, start, end,
+                                                   0, 0, NULL);
                } else {
                        /* try making a compressed inline extent */
-                       ret = cow_file_range_inline(trans, root, inode,
-                                                   start, end,
+                       ret = cow_file_range_inline(root, inode, start, end,
                                                    total_compressed,
                                                    compress_type, pages);
                }
@@ -498,10 +499,8 @@ cont:
                                                     PAGE_CLEAR_DIRTY |
                                                     PAGE_SET_WRITEBACK |
                                                     PAGE_END_WRITEBACK);
-                       btrfs_end_transaction(trans, root);
                        goto free_pages_out;
                }
-               btrfs_end_transaction(trans, root);
        }
 
        if (will_compress) {
@@ -592,18 +591,6 @@ free_pages_out:
        kfree(pages);
 
        goto out;
-
-cleanup_and_out:
-       extent_clear_unlock_delalloc(inode, start, end, NULL,
-                                    EXTENT_DELALLOC | EXTENT_DO_ACCOUNTING |
-                                    EXTENT_DEFRAG, PAGE_UNLOCK |
-                                    PAGE_CLEAR_DIRTY | PAGE_SET_WRITEBACK |
-                                    PAGE_END_WRITEBACK);
-       if (!trans || IS_ERR(trans))
-               btrfs_error(root->fs_info, ret, "Failed to join transaction");
-       else
-               btrfs_abort_transaction(trans, root, ret);
-       goto free_pages_out;
 }
 
 /*
@@ -617,7 +604,6 @@ static noinline int submit_compressed_extents(struct inode *inode,
 {
        struct async_extent *async_extent;
        u64 alloc_hint = 0;
-       struct btrfs_trans_handle *trans;
        struct btrfs_key ins;
        struct extent_map *em;
        struct btrfs_root *root = BTRFS_I(inode)->root;
@@ -678,20 +664,10 @@ retry:
                lock_extent(io_tree, async_extent->start,
                            async_extent->start + async_extent->ram_size - 1);
 
-               trans = btrfs_join_transaction(root);
-               if (IS_ERR(trans)) {
-                       ret = PTR_ERR(trans);
-               } else {
-                       trans->block_rsv = &root->fs_info->delalloc_block_rsv;
-                       ret = btrfs_reserve_extent(trans, root,
+               ret = btrfs_reserve_extent(root,
                                           async_extent->compressed_size,
                                           async_extent->compressed_size,
                                           0, alloc_hint, &ins, 1);
-                       if (ret && ret != -ENOSPC)
-                               btrfs_abort_transaction(trans, root, ret);
-                       btrfs_end_transaction(trans, root);
-               }
-
                if (ret) {
                        int i;
 
@@ -850,14 +826,13 @@ static u64 get_extent_allocation_hint(struct inode *inode, u64 start,
  * required to start IO on it.  It may be clean and already done with
  * IO when we return.
  */
-static noinline int __cow_file_range(struct btrfs_trans_handle *trans,
-                                    struct inode *inode,
-                                    struct btrfs_root *root,
-                                    struct page *locked_page,
-                                    u64 start, u64 end, int *page_started,
-                                    unsigned long *nr_written,
-                                    int unlock)
+static noinline int cow_file_range(struct inode *inode,
+                                  struct page *locked_page,
+                                  u64 start, u64 end, int *page_started,
+                                  unsigned long *nr_written,
+                                  int unlock)
 {
+       struct btrfs_root *root = BTRFS_I(inode)->root;
        u64 alloc_hint = 0;
        u64 num_bytes;
        unsigned long ram_size;
@@ -878,12 +853,12 @@ static noinline int __cow_file_range(struct btrfs_trans_handle *trans,
        /* if this is a small write inside eof, kick off defrag */
        if (num_bytes < 64 * 1024 &&
            (start > 0 || end + 1 < BTRFS_I(inode)->disk_i_size))
-               btrfs_add_inode_defrag(trans, inode);
+               btrfs_add_inode_defrag(NULL, inode);
 
        if (start == 0) {
                /* lets try to make an inline extent */
-               ret = cow_file_range_inline(trans, root, inode,
-                                           start, end, 0, 0, NULL);
+               ret = cow_file_range_inline(root, inode, start, end, 0, 0,
+                                           NULL);
                if (ret == 0) {
                        extent_clear_unlock_delalloc(inode, start, end, NULL,
                                     EXTENT_LOCKED | EXTENT_DELALLOC |
@@ -896,7 +871,6 @@ static noinline int __cow_file_range(struct btrfs_trans_handle *trans,
                        *page_started = 1;
                        goto out;
                } else if (ret < 0) {
-                       btrfs_abort_transaction(trans, root, ret);
                        goto out_unlock;
                }
        }
@@ -911,13 +885,11 @@ static noinline int __cow_file_range(struct btrfs_trans_handle *trans,
                unsigned long op;
 
                cur_alloc_size = disk_num_bytes;
-               ret = btrfs_reserve_extent(trans, root, cur_alloc_size,
+               ret = btrfs_reserve_extent(root, cur_alloc_size,
                                           root->sectorsize, 0, alloc_hint,
                                           &ins, 1);
-               if (ret < 0) {
-                       btrfs_abort_transaction(trans, root, ret);
+               if (ret < 0)
                        goto out_unlock;
-               }
 
                em = alloc_extent_map();
                if (!em) {
@@ -963,10 +935,8 @@ static noinline int __cow_file_range(struct btrfs_trans_handle *trans,
                    BTRFS_DATA_RELOC_TREE_OBJECTID) {
                        ret = btrfs_reloc_clone_csums(inode, start,
                                                      cur_alloc_size);
-                       if (ret) {
-                               btrfs_abort_transaction(trans, root, ret);
+                       if (ret)
                                goto out_reserve;
-                       }
                }
 
                if (disk_num_bytes < cur_alloc_size)
@@ -1005,37 +975,6 @@ out_unlock:
        goto out;
 }
 
-static noinline int cow_file_range(struct inode *inode,
-                                  struct page *locked_page,
-                                  u64 start, u64 end, int *page_started,
-                                  unsigned long *nr_written,
-                                  int unlock)
-{
-       struct btrfs_trans_handle *trans;
-       struct btrfs_root *root = BTRFS_I(inode)->root;
-       int ret;
-
-       trans = btrfs_join_transaction(root);
-       if (IS_ERR(trans)) {
-               extent_clear_unlock_delalloc(inode, start, end, locked_page,
-                                            EXTENT_LOCKED | EXTENT_DELALLOC |
-                                            EXTENT_DO_ACCOUNTING |
-                                            EXTENT_DEFRAG, PAGE_UNLOCK |
-                                            PAGE_CLEAR_DIRTY |
-                                            PAGE_SET_WRITEBACK |
-                                            PAGE_END_WRITEBACK);
-               return PTR_ERR(trans);
-       }
-       trans->block_rsv = &root->fs_info->delalloc_block_rsv;
-
-       ret = __cow_file_range(trans, inode, root, locked_page, start, end,
-                              page_started, nr_written, unlock);
-
-       btrfs_end_transaction(trans, root);
-
-       return ret;
-}
-
 /*
  * work queue call back to started compression on a file and pages
  */
@@ -1347,9 +1286,9 @@ out_check:
 
                btrfs_release_path(path);
                if (cow_start != (u64)-1) {
-                       ret = __cow_file_range(trans, inode, root, locked_page,
-                                              cow_start, found_key.offset - 1,
-                                              page_started, nr_written, 1);
+                       ret = cow_file_range(inode, locked_page,
+                                            cow_start, found_key.offset - 1,
+                                            page_started, nr_written, 1);
                        if (ret) {
                                btrfs_abort_transaction(trans, root, ret);
                                goto error;
@@ -1423,9 +1362,8 @@ out_check:
        }
 
        if (cow_start != (u64)-1) {
-               ret = __cow_file_range(trans, inode, root, locked_page,
-                                      cow_start, end,
-                                      page_started, nr_written, 1);
+               ret = cow_file_range(inode, locked_page, cow_start, end,
+                                    page_started, nr_written, 1);
                if (ret) {
                        btrfs_abort_transaction(trans, root, ret);
                        goto error;
@@ -6344,39 +6282,32 @@ static struct extent_map *btrfs_new_extent_direct(struct inode *inode,
                                                  u64 start, u64 len)
 {
        struct btrfs_root *root = BTRFS_I(inode)->root;
-       struct btrfs_trans_handle *trans;
        struct extent_map *em;
        struct btrfs_key ins;
        u64 alloc_hint;
        int ret;
 
-       trans = btrfs_join_transaction(root);
-       if (IS_ERR(trans))
-               return ERR_CAST(trans);
-
-       trans->block_rsv = &root->fs_info->delalloc_block_rsv;
-
        alloc_hint = get_extent_allocation_hint(inode, start, len);
-       ret = btrfs_reserve_extent(trans, root, len, root->sectorsize, 0,
+       ret = btrfs_reserve_extent(root, len, root->sectorsize, 0,
                                   alloc_hint, &ins, 1);
-       if (ret) {
-               em = ERR_PTR(ret);
-               goto out;
-       }
+       if (ret)
+               return ERR_PTR(ret);
 
        em = create_pinned_em(inode, start, ins.offset, start, ins.objectid,
                              ins.offset, ins.offset, ins.offset, 0);
-       if (IS_ERR(em))
-               goto out;
+       if (IS_ERR(em)) {
+               btrfs_free_reserved_extent(root, ins.objectid, ins.offset);
+               return em;
+       }
 
        ret = btrfs_add_ordered_extent_dio(inode, start, ins.objectid,
                                           ins.offset, ins.offset, 0);
        if (ret) {
                btrfs_free_reserved_extent(root, ins.objectid, ins.offset);
-               em = ERR_PTR(ret);
+               free_extent_map(em);
+               return ERR_PTR(ret);
        }
-out:
-       btrfs_end_transaction(trans, root);
+
        return em;
 }
 
@@ -6384,11 +6315,11 @@ out:
  * returns 1 when the nocow is safe, < 1 on error, 0 if the
  * block must be cow'd
  */
-noinline int can_nocow_extent(struct btrfs_trans_handle *trans,
-                             struct inode *inode, u64 offset, u64 *len,
+noinline int can_nocow_extent(struct inode *inode, u64 offset, u64 *len,
                              u64 *orig_start, u64 *orig_block_len,
                              u64 *ram_bytes)
 {
+       struct btrfs_trans_handle *trans;
        struct btrfs_path *path;
        int ret;
        struct extent_buffer *leaf;
@@ -6406,7 +6337,7 @@ noinline int can_nocow_extent(struct btrfs_trans_handle *trans,
        if (!path)
                return -ENOMEM;
 
-       ret = btrfs_lookup_file_extent(trans, root, path, btrfs_ino(inode),
+       ret = btrfs_lookup_file_extent(NULL, root, path, btrfs_ino(inode),
                                       offset, 0);
        if (ret < 0)
                goto out;
@@ -6471,9 +6402,19 @@ noinline int can_nocow_extent(struct btrfs_trans_handle *trans,
         * look for other files referencing this extent, if we
         * find any we must cow
         */
-       if (btrfs_cross_ref_exist(trans, root, btrfs_ino(inode),
-                                 key.offset - backref_offset, disk_bytenr))
+       trans = btrfs_join_transaction(root);
+       if (IS_ERR(trans)) {
+               ret = 0;
                goto out;
+       }
+
+       ret = btrfs_cross_ref_exist(trans, root, btrfs_ino(inode),
+                                   key.offset - backref_offset, disk_bytenr);
+       btrfs_end_transaction(trans, root);
+       if (ret) {
+               ret = 0;
+               goto out;
+       }
 
        /*
         * adjust disk_bytenr and num_bytes to cover just the bytes
@@ -6615,7 +6556,6 @@ static int btrfs_get_blocks_direct(struct inode *inode, sector_t iblock,
        u64 start = iblock << inode->i_blkbits;
        u64 lockstart, lockend;
        u64 len = bh_result->b_size;
-       struct btrfs_trans_handle *trans;
        int unlock_bits = EXTENT_LOCKED;
        int ret = 0;
 
@@ -6697,16 +6637,7 @@ static int btrfs_get_blocks_direct(struct inode *inode, sector_t iblock,
                len = min(len, em->len - (start - em->start));
                block_start = em->block_start + (start - em->start);
 
-               /*
-                * we're not going to log anything, but we do need
-                * to make sure the current transaction stays open
-                * while we look for nocow cross refs
-                */
-               trans = btrfs_join_transaction(root);
-               if (IS_ERR(trans))
-                       goto must_cow;
-
-               if (can_nocow_extent(trans, inode, start, &len, &orig_start,
+               if (can_nocow_extent(inode, start, &len, &orig_start,
                                     &orig_block_len, &ram_bytes) == 1) {
                        if (type == BTRFS_ORDERED_PREALLOC) {
                                free_extent_map(em);
@@ -6715,24 +6646,20 @@ static int btrfs_get_blocks_direct(struct inode *inode, sector_t iblock,
                                                       block_start, len,
                                                       orig_block_len,
                                                       ram_bytes, type);
-                               if (IS_ERR(em)) {
-                                       btrfs_end_transaction(trans, root);
+                               if (IS_ERR(em))
                                        goto unlock_err;
-                               }
                        }
 
                        ret = btrfs_add_ordered_extent_dio(inode, start,
                                           block_start, len, len, type);
-                       btrfs_end_transaction(trans, root);
                        if (ret) {
                                free_extent_map(em);
                                goto unlock_err;
                        }
                        goto unlock;
                }
-               btrfs_end_transaction(trans, root);
        }
-must_cow:
+
        /*
         * this will cow the extent, reset the len in case we changed
         * it above
@@ -8495,8 +8422,8 @@ static int __btrfs_prealloc_file_range(struct inode *inode, int mode,
 
                cur_bytes = min(num_bytes, 256ULL * 1024 * 1024);
                cur_bytes = max(cur_bytes, min_size);
-               ret = btrfs_reserve_extent(trans, root, cur_bytes,
-                                          min_size, 0, *alloc_hint, &ins, 1);
+               ret = btrfs_reserve_extent(root, cur_bytes, min_size, 0,
+                                          *alloc_hint, &ins, 1);
                if (ret) {
                        if (own_trans)
                                btrfs_end_transaction(trans, root);