Re: [PATCH 09/12] xfs: refactor the ioend merging code

Nikolay Borisov
2019-06-24T16:06:28Z

On 24.06.19 г. 8:52 ч., Christoph Hellwig wrote:
> Introduce two nicely abstracted helper, which can be moved to the
> iomap code later. Also use list_pop and list_first_entry_or_null
> to simplify the code a bit.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
> fs/xfs/xfs_aops.c | 66 ++++++++++++++++++++++++++---------------------
> 1 file changed, 36 insertions(+), 30 deletions(-)
>
> diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
> index acbd73976067..5d302ebe2a33 100644
> --- a/fs/xfs/xfs_aops.c
> +++ b/fs/xfs/xfs_aops.c
> @@ -121,6 +121,19 @@ xfs_destroy_ioend(
> }
> }
>
> +static void
> +xfs_destroy_ioends(
> + struct xfs_ioend *ioend,
> + int error)
> +{
> + struct list_head tmp;
> +
> + list_replace_init(&ioend->io_list, &tmp);
> + xfs_destroy_ioend(ioend, error);
> + while ((ioend = list_pop(&tmp, struct xfs_ioend, io_list)))
> + xfs_destroy_ioend(ioend, error);

nit: I'd prefer if the list_pop patch is right before this one since
this is the first user of it. Additionally, I don't think list_pop is
really a net-negative win in comparison to list_for_each_entry_safe
here. In fact this "delete the list" would seems more idiomatic if
implemented via list_for_each_entry_safe

> +}
> +
> /*
> * Fast and loose check if this write could update the on-disk inode size.
> */
> @@ -173,7 +186,6 @@ xfs_end_ioend(
> struct xfs_ioend *ioend)
> {
> unsigned int nofs_flag = memalloc_nofs_save();
> - struct list_head ioend_list;
> struct xfs_inode *ip = XFS_I(ioend->io_inode);
> xfs_off_t offset = ioend->io_offset;
> size_t size = ioend->io_size;
> @@ -207,16 +219,7 @@ xfs_end_ioend(
> if (!error && xfs_ioend_is_append(ioend))
> error = xfs_setfilesize(ip, offset, size);
> done:
> - list_replace_init(&ioend->io_list, &ioend_list);
> - xfs_destroy_ioend(ioend, error);
> -
> - while (!list_empty(&ioend_list)) {
> - ioend = list_first_entry(&ioend_list, struct xfs_ioend,
> - io_list);
> - list_del_init(&ioend->io_list);
> - xfs_destroy_ioend(ioend, error);
> - }
> -
> + xfs_destroy_ioends(ioend, error);
> memalloc_nofs_restore(nofs_flag);
> }
>
> @@ -246,15 +249,16 @@ xfs_ioend_try_merge(
> struct xfs_ioend *ioend,
> struct list_head *more_ioends)
> {
> - struct xfs_ioend *next_ioend;
> + struct xfs_ioend *next;
>
> - while (!list_empty(more_ioends)) {
> - next_ioend = list_first_entry(more_ioends, struct xfs_ioend,
> - io_list);
> - if (!xfs_ioend_can_merge(ioend, next_ioend))
> + INIT_LIST_HEAD(&ioend->io_list);
> +
> + while ((next = list_first_entry_or_null(more_ioends, struct xfs_ioend,
> + io_list))) {
> + if (!xfs_ioend_can_merge(ioend, next))
> break;
> - list_move_tail(&next_ioend->io_list, &ioend->io_list);
> - ioend->io_size += next_ioend->io_size;
> + list_move_tail(&next->io_list, &ioend->io_list);
> + ioend->io_size += next->io_size;
> }
> }
>
> @@ -277,29 +281,31 @@ xfs_ioend_compare(
> return 0;
> }
>
> +static void
> +xfs_sort_ioends(
> + struct list_head *ioend_list)
> +{
> + list_sort(NULL, ioend_list, xfs_ioend_compare);
> +}
> +
> /* Finish all pending io completions. */
> void
> xfs_end_io(
> struct work_struct *work)
> {
> - struct xfs_inode *ip;
> + struct xfs_inode *ip =
> + container_of(work, struct xfs_inode, i_ioend_work);
> struct xfs_ioend *ioend;
> - struct list_head completion_list;
> + struct list_head tmp;
> unsigned long flags;
>
> - ip = container_of(work, struct xfs_inode, i_ioend_work);
> -
> spin_lock_irqsave(&ip->i_ioend_lock, flags);
> - list_replace_init(&ip->i_ioend_list, &completion_list);
> + list_replace_init(&ip->i_ioend_list, &tmp);
> spin_unlock_irqrestore(&ip->i_ioend_lock, flags);
>
> - list_sort(NULL, &completion_list, xfs_ioend_compare);
> -
> - while (!list_empty(&completion_list)) {
> - ioend = list_first_entry(&completion_list, struct xfs_ioend,
> - io_list);
> - list_del_init(&ioend->io_list);
> - xfs_ioend_try_merge(ioend, &completion_list);
> + xfs_sort_ioends(&tmp);
> + while ((ioend = list_pop(&tmp, struct xfs_ioend, io_list))) {
> + xfs_ioend_try_merge(ioend, &tmp);
> xfs_end_ioend(ioend);

Here again, tmp is a local copy that is immutable so using while()
instead of list_for_each_entry_safe doesn't seem to be providing much.

> }
> }
>