Re: [PATCH v2 10/12] btrfs: make balance_dirty_pages nowait compatible

[Filipe Manana <fdmanana@kernel.org>]

On Thu, Sep 8, 2022 at 1:26 AM Stefan Roesch <shr@fb.com> wrote:
>
> This replaces the call to function balance_dirty_pages_ratelimited() in
> the function btrfs_buffered_write() with a call to
> balance_dirty_pages_ratelimited_flags().
>
> It also moves the function after the again label. This can cause the
> function to be called a bit later, but this should have no impact in the
> real world.
>
> Signed-off-by: Stefan Roesch <shr@fb.com>
> ---
>  fs/btrfs/file.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
> index 6e191e353b22..fd42ba9de7a7 100644
> --- a/fs/btrfs/file.c
> +++ b/fs/btrfs/file.c
> @@ -1654,6 +1654,7 @@ static noinline ssize_t btrfs_buffered_write(struct kiocb *iocb,
>         loff_t old_isize = i_size_read(inode);
>         unsigned int ilock_flags = 0;
>         bool nowait = iocb->ki_flags & IOCB_NOWAIT;
> +       unsigned int bdp_flags = nowait ? BDP_ASYNC : 0;
>
>         if (nowait)
>                 ilock_flags |= BTRFS_ILOCK_TRY;
> @@ -1756,6 +1757,10 @@ static noinline ssize_t btrfs_buffered_write(struct kiocb *iocb,
>
>                 release_bytes = reserve_bytes;
>  again:
> +               ret = balance_dirty_pages_ratelimited_flags(inode->i_mapping, bdp_flags);
> +               if (unlikely(ret))

We normally only use likely or unlikely in contextes where we observe
that it makes a significant difference.
What's the motivation here, have you verified that in this case it has
a significant impact?

Thanks.

> +                       break;
> +
>                 /*
>                  * This is going to setup the pages array with the number of
>                  * pages we want, so we don't really need to worry about the
> @@ -1860,8 +1865,6 @@ static noinline ssize_t btrfs_buffered_write(struct kiocb *iocb,
>
>                 cond_resched();
>
> -               balance_dirty_pages_ratelimited(inode->i_mapping);
> -
>                 pos += copied;
>                 num_written += copied;
>         }
> --
> 2.30.2
>