Excerpts from Josef Bacik's message of 2011-04-15 12:56:15 -0400:
> We currently track trans handles in current->journal_info, but we don't actually
> use it. This patch fixes it. This will cover the case where we have multiple
> people starting transactions down the call chain. This keeps us from having to
> allocate a new handle and all of that, we just increase the use count of the
> current handle, save the old block_rsv, and return. I tested this with xfstests
> and it worked out fine. Thanks,
Just curious, which call stacks are currently nesting transactions?
-chris
>
> Signed-off-by: Josef Bacik <josef@xxxxxxxxxx>
> ---
> fs/btrfs/transaction.c | 17 +++++++++++++++++
> fs/btrfs/transaction.h | 2 ++
> 2 files changed, 19 insertions(+), 0 deletions(-)
>
> diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
> index 70bfb26..46f4056 100644
> --- a/fs/btrfs/transaction.c
> +++ b/fs/btrfs/transaction.c
> @@ -184,6 +184,15 @@ static struct btrfs_trans_handle *start_transaction(struct btrfs_root *root,
>
> if (root->fs_info->fs_state & BTRFS_SUPER_FLAG_ERROR)
> return ERR_PTR(-EROFS);
> +
> + if (current->journal_info) {
> + WARN_ON(type != TRANS_JOIN && type != TRANS_JOIN_NOLOCK);
> + h = current->journal_info;
> + h->use_count++;
> + h->orig_rsv = h->block_rsv;
> + h->block_rsv = NULL;
> + goto got_it;
> + }
> again:
> h = kmem_cache_alloc(btrfs_trans_handle_cachep, GFP_NOFS);
> if (!h)
> @@ -213,7 +222,9 @@ again:
> h->block_group = 0;
> h->bytes_reserved = 0;
> h->delayed_ref_updates = 0;
> + h->use_count = 1;
> h->block_rsv = NULL;
> + h->orig_rsv = NULL;
>
> smp_mb();
> if (cur_trans->blocked && may_wait_transaction(root, type)) {
> @@ -241,6 +252,7 @@ again:
> }
> }
>
> +got_it:
> if (type != TRANS_JOIN_NOLOCK)
> mutex_lock(&root->fs_info->trans_mutex);
> record_root_in_trans(h, root);
> @@ -428,6 +440,11 @@ static int __btrfs_end_transaction(struct btrfs_trans_handle *trans,
> struct btrfs_fs_info *info = root->fs_info;
> int count = 0;
>
> + if (--trans->use_count) {
> + trans->block_rsv = trans->orig_rsv;
> + return 0;
> + }
> +
> while (count < 4) {
> unsigned long cur = trans->delayed_ref_updates;
> trans->delayed_ref_updates = 0;
> diff --git a/fs/btrfs/transaction.h b/fs/btrfs/transaction.h
> index 1f573f0..154314f 100644
> --- a/fs/btrfs/transaction.h
> +++ b/fs/btrfs/transaction.h
> @@ -47,11 +47,13 @@ struct btrfs_trans_handle {
> u64 transid;
> u64 block_group;
> u64 bytes_reserved;
> + unsigned long use_count;
> unsigned long blocks_reserved;
> unsigned long blocks_used;
> unsigned long delayed_ref_updates;
> struct btrfs_transaction *transaction;
> struct btrfs_block_rsv *block_rsv;
> + struct btrfs_block_rsv *orig_rsv;
> };
>
> struct btrfs_pending_snapshot {
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