On 18.06.19 г. 17:59 ч., Josef Bacik wrote:
> We have been seeing issues in production where a cleaner script will end
> up unlinking a bunch of files that have pending iputs. This means they
> will get their final iput's run at btrfs-cleaner time and thus are not
> throttled, which impacts the workload.
>
> Since we are unlinking these files we can just drop the delayed iput at
> unlink time. We are already holding a reference to the inode so this
> will not be the final iput and thus is completely safe to do at this
> point. Doing this means we are more likely to be doing the final iput
> at unlink time, and thus will get the IO charged to the caller and get
> throttled appropriately without affecting the main workload.
>
> Signed-off-by: Josef Bacik <jo...@toxicpanda.com>
That looks a lot nicer and the explanation is sufficient.
Reviewed-by: Nikolay Borisov <nbori...@suse.com>
> ---
> v1->v2:
> - consolidate the delayed iput run into a helper.
>
> fs/btrfs/inode.c | 40 ++++++++++++++++++++++++++++++++++------
> 1 file changed, 34 insertions(+), 6 deletions(-)
>
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index 33380f5e2e8a..c311bf6d52f4 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -3326,6 +3326,28 @@ void btrfs_add_delayed_iput(struct inode *inode)
> wake_up_process(fs_info->cleaner_kthread);
> }
>
> +static void run_delayed_iput_locked(struct btrfs_fs_info *fs_info,
> + struct btrfs_inode *inode)
> +{
> + 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);
> +}
> +
> +static void btrfs_run_delayed_iput(struct btrfs_fs_info *fs_info,
> + struct btrfs_inode *inode)
> +{
> + if (!list_empty(&inode->delayed_iput)) {
> + spin_lock(&fs_info->delayed_iput_lock);
> + if (!list_empty(&inode->delayed_iput))
> + run_delayed_iput_locked(fs_info, inode);
> + spin_unlock(&fs_info->delayed_iput_lock);
> + }
> +}
> +
> void btrfs_run_delayed_iputs(struct btrfs_fs_info *fs_info)
> {
>
> @@ -3335,12 +3357,7 @@ void btrfs_run_delayed_iputs(struct btrfs_fs_info
> *fs_info)
>
> inode = list_first_entry(&fs_info->delayed_iputs,
> struct btrfs_inode, delayed_iput);
> - 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);
> + run_delayed_iput_locked(fs_info, inode);
> }
> spin_unlock(&fs_info->delayed_iput_lock);
> }
> @@ -4045,6 +4062,17 @@ static int __btrfs_unlink_inode(struct
> btrfs_trans_handle *trans,
> ret = 0;
> else if (ret)
> btrfs_abort_transaction(trans, ret);
> +
> + /*
> + * If we have a pending delayed iput we could end up with the final iput
> + * being run in btrfs-cleaner context. If we have enough of these built
> + * up we can end up burning a lot of time in btrfs-cleaner without any
> + * way to throttle the unlinks. Since we're currently holding a ref on
> + * the inode we can run the delayed iput here without any issues as the
> + * final iput won't be done until after we drop the ref we're currently
> + * holding.
> + */
> + btrfs_run_delayed_iput(fs_info, inode);
> err:
> btrfs_free_path(path);
> if (ret)
>
