On Thu, Sep 07, 2017 at 11:22:20AM -0600, Liu Bo wrote:
> This was intended to congest higher layers to not send bios, but as
>
> 1) the congested bit has been taken by writeback
Can you please be more specific here?
> 2) and no one is waiting for %nr_async_bios down to zero,
>
> we can safely remove this now.
>From the original commit it looks like mechanism to avoid some write
patterns (streaming not becoming random), but the commit is from 2008,
lot of things have changed.
I think we should at least document whats' the congestion behaviour we
rely on nowadays, so that' sfor the 1). Otherwise patch looks ok.
>
> Signed-off-by: Liu Bo <bo.li.liu@xxxxxxxxxx>
> ---
> fs/btrfs/ctree.h | 1 -
> fs/btrfs/disk-io.c | 1 -
> fs/btrfs/volumes.c | 14 --------------
> 3 files changed, 16 deletions(-)
>
> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
> index 3f3eb7b..27cd882 100644
> --- a/fs/btrfs/ctree.h
> +++ b/fs/btrfs/ctree.h
> @@ -881,7 +881,6 @@ struct btrfs_fs_info {
>
> atomic_t nr_async_submits;
> atomic_t async_submit_draining;
> - atomic_t nr_async_bios;
> atomic_t async_delalloc_pages;
> atomic_t open_ioctl_trans;
>
> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
> index f45b61f..95583e2 100644
> --- a/fs/btrfs/disk-io.c
> +++ b/fs/btrfs/disk-io.c
> @@ -2657,7 +2657,6 @@ int open_ctree(struct super_block *sb,
> atomic_set(&fs_info->nr_async_submits, 0);
> atomic_set(&fs_info->async_delalloc_pages, 0);
> atomic_set(&fs_info->async_submit_draining, 0);
> - atomic_set(&fs_info->nr_async_bios, 0);
> atomic_set(&fs_info->defrag_running, 0);
> atomic_set(&fs_info->qgroup_op_seq, 0);
> atomic_set(&fs_info->reada_works_cnt, 0);
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index bd679bc..6e9df4d 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -450,13 +450,6 @@ static noinline void run_scheduled_bios(struct btrfs_device *device)
> pending = pending->bi_next;
> cur->bi_next = NULL;
>
> - /*
> - * atomic_dec_return implies a barrier for waitqueue_active
> - */
> - if (atomic_dec_return(&fs_info->nr_async_bios) < limit &&
And after that the variable 'limit' becomes unused, please remove it as
well.
> - waitqueue_active(&fs_info->async_submit_wait))
> - wake_up(&fs_info->async_submit_wait);
> -
> BUG_ON(atomic_read(&cur->__bi_cnt) == 0);
>
> /*
> @@ -6132,13 +6125,6 @@ static noinline void btrfs_schedule_bio(struct btrfs_device *device,
> return;
> }
>
> - /*
> - * nr_async_bios allows us to reliably return congestion to the
> - * higher layers. Otherwise, the async bio makes it appear we have
> - * made progress against dirty pages when we've really just put it
> - * on a queue for later
> - */
> - atomic_inc(&fs_info->nr_async_bios);
> WARN_ON(bio->bi_next);
> bio->bi_next = NULL;
>
> --
> 2.9.4
>
> --
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