On 21.11.18 г. 21:09 ч., Josef Bacik wrote:
> The throttle path doesn't take cleaner_delayed_iput_mutex, which means
Which one is the throttle path? btrfs_end_transaction_throttle is only
called during snapshot drop and relocation? What scenario triggered your
observation and prompted this fix?
> we could think we're done flushing iputs in the data space reservation
> path when we could have a throttler doing an iput. There's no real
> reason to serialize the delayed iput flushing, so instead of taking the
> cleaner_delayed_iput_mutex whenever we flush the delayed iputs just
> replace it with an atomic counter and a waitqueue. This removes the
> short (or long depending on how big the inode is) window where we think
> there are no more pending iputs when there really are some.
>
> Signed-off-by: Josef Bacik <jo...@toxicpanda.com>
> ---
> fs/btrfs/ctree.h | 4 +++-
> fs/btrfs/disk-io.c | 5 ++---
> fs/btrfs/extent-tree.c | 9 +++++----
> fs/btrfs/inode.c | 21 +++++++++++++++++++++
> 4 files changed, 31 insertions(+), 8 deletions(-)
>
> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
> index 709de7471d86..a835fe7076eb 100644
> --- a/fs/btrfs/ctree.h
> +++ b/fs/btrfs/ctree.h
> @@ -912,7 +912,8 @@ struct btrfs_fs_info {
>
> spinlock_t delayed_iput_lock;
> struct list_head delayed_iputs;
> - struct mutex cleaner_delayed_iput_mutex;
> + atomic_t nr_delayed_iputs;
> + wait_queue_head_t delayed_iputs_wait;
>
> /* this protects tree_mod_seq_list */
> spinlock_t tree_mod_seq_lock;
> @@ -3237,6 +3238,7 @@ int btrfs_orphan_cleanup(struct btrfs_root *root);
> int btrfs_cont_expand(struct inode *inode, loff_t oldsize, loff_t size);
> void btrfs_add_delayed_iput(struct inode *inode);
> void btrfs_run_delayed_iputs(struct btrfs_fs_info *fs_info);
> +int btrfs_wait_on_delayed_iputs(struct btrfs_fs_info *fs_info);
> int btrfs_prealloc_file_range(struct inode *inode, int mode,
> u64 start, u64 num_bytes, u64 min_size,
> loff_t actual_len, u64 *alloc_hint);
> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
> index c5918ff8241b..3f81dfaefa32 100644
> --- a/fs/btrfs/disk-io.c
> +++ b/fs/btrfs/disk-io.c
> @@ -1692,9 +1692,7 @@ static int cleaner_kthread(void *arg)
> goto sleep;
> }
>
> - mutex_lock(&fs_info->cleaner_delayed_iput_mutex);
> btrfs_run_delayed_iputs(fs_info);
> - mutex_unlock(&fs_info->cleaner_delayed_iput_mutex);
>
> again = btrfs_clean_one_deleted_snapshot(root);
> mutex_unlock(&fs_info->cleaner_mutex);
> @@ -2651,7 +2649,6 @@ int open_ctree(struct super_block *sb,
> mutex_init(&fs_info->delete_unused_bgs_mutex);
> mutex_init(&fs_info->reloc_mutex);
> mutex_init(&fs_info->delalloc_root_mutex);
> - mutex_init(&fs_info->cleaner_delayed_iput_mutex);
> seqlock_init(&fs_info->profiles_lock);
>
> INIT_LIST_HEAD(&fs_info->dirty_cowonly_roots);
> @@ -2673,6 +2670,7 @@ int open_ctree(struct super_block *sb,
> atomic_set(&fs_info->defrag_running, 0);
> atomic_set(&fs_info->qgroup_op_seq, 0);
> atomic_set(&fs_info->reada_works_cnt, 0);
> + atomic_set(&fs_info->nr_delayed_iputs, 0);
> atomic64_set(&fs_info->tree_mod_seq, 0);
> fs_info->sb = sb;
> fs_info->max_inline = BTRFS_DEFAULT_MAX_INLINE;
> @@ -2750,6 +2748,7 @@ int open_ctree(struct super_block *sb,
> init_waitqueue_head(&fs_info->transaction_wait);
> init_waitqueue_head(&fs_info->transaction_blocked_wait);
> init_waitqueue_head(&fs_info->async_submit_wait);
> + init_waitqueue_head(&fs_info->delayed_iputs_wait);
>
> INIT_LIST_HEAD(&fs_info->pinned_chunks);
>
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index 3a90dc1d6b31..36f43876be22 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -4272,8 +4272,9 @@ int btrfs_alloc_data_chunk_ondemand(struct btrfs_inode
> *inode, u64 bytes)
> * operations. Wait for it to finish so that
> * more space is released.
> */
> -
> mutex_lock(&fs_info->cleaner_delayed_iput_mutex);
> -
> mutex_unlock(&fs_info->cleaner_delayed_iput_mutex);
> + ret = btrfs_wait_on_delayed_iputs(fs_info);
> + if (ret)
> + return ret;
> goto again;
> } else {
> btrfs_end_transaction(trans);
> @@ -4838,9 +4839,9 @@ static int may_commit_transaction(struct btrfs_fs_info
> *fs_info,
> * pinned space, so make sure we run the iputs before we do our pinned
> * bytes check below.
> */
> - mutex_lock(&fs_info->cleaner_delayed_iput_mutex);
> btrfs_run_delayed_iputs(fs_info);
> - mutex_unlock(&fs_info->cleaner_delayed_iput_mutex);
> + wait_event(fs_info->delayed_iputs_wait,
> + atomic_read(&fs_info->nr_delayed_iputs) == 0);
Why open code btrfs_wait_on_delayed_iputs(fs_info)? Just make it use
wait_event instead of the killable version and use the function
uniformally across the code base.
>
> trans = btrfs_join_transaction(fs_info->extent_root);
> if (IS_ERR(trans))
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index 3c42d8887183..57bf514a90eb 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -3260,6 +3260,7 @@ void btrfs_add_delayed_iput(struct inode *inode)
> if (atomic_add_unless(&inode->i_count, -1, 1))
> return;
>
> + atomic_inc(&fs_info->nr_delayed_iputs);
> spin_lock(&fs_info->delayed_iput_lock);
> ASSERT(list_empty(&binode->delayed_iput));
> list_add_tail(&binode->delayed_iput, &fs_info->delayed_iputs);
> @@ -3279,11 +3280,31 @@ void btrfs_run_delayed_iputs(struct btrfs_fs_info
> *fs_info)
> list_del_init(&inode->delayed_iput);
> spin_unlock(&fs_info->delayed_iput_lock);
> iput(&inode->vfs_inode);
> + if (atomic_dec_and_test(&fs_info->nr_delayed_iputs))
> + wake_up(&fs_info->delayed_iputs_wait);
> spin_lock(&fs_info->delayed_iput_lock);
> }
> spin_unlock(&fs_info->delayed_iput_lock);
> }
>
> +/**
> + * btrfs_wait_on_delayed_iputs - wait on the delayed iputs to be done running
> + * @fs_info - the fs_info for this fs
> + * @return - EINTR if we were killed, 0 if nothing's pending
> + *
> + * This will wait on any delayed iputs that are currently running with
> KILLABLE
> + * set. Once they are all done running we will return, unless we are killed
> in
> + * which case we return EINTR.
> + */
> +int btrfs_wait_on_delayed_iputs(struct btrfs_fs_info *fs_info)
> +{
> + int ret = wait_event_killable(fs_info->delayed_iputs_wait,
> + atomic_read(&fs_info->nr_delayed_iputs) == 0);
> + if (ret)
> + return -EINTR;
> + return 0;
> +}
> +
> /*
> * This creates an orphan entry for the given inode in case something goes
> wrong
> * in the middle of an unlink.
>
