linux-ext4 - Re: [PATCH 1/2] fs-writeback: Add helper function to start writeback if idle

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Date:	Wed, 16 Dec 2009 21:44:09 +0100
From:	Jan Kara <jack@...e.cz>
To:	Eric Sandeen <sandeen@...hat.com>
Cc:	ext4 development <linux-ext4@...r.kernel.org>,
	linux-fsdevel@...r.kernel.org, Jens Axboe <jens.axboe@...cle.com>
Subject: Re: [PATCH 1/2] fs-writeback: Add helper function to start writeback if idle

> ext4, at least, would like to start pushing on writeback if it starts
> to get close to ENOSPC when reserving worst-case blocks for delalloc
> writes.  Writing out delalloc data will convert those worst-case
> predictions into usually smaller actual usage, freeing up space
> before we hit ENOSPC based on this speculation.
> 
> Thanks to Jens for the suggestion for the helper function,
> & the naming help.
> 
> I've made the helper return status on whether writeback was
> started even though I don't plan to use it in the ext4 patch;
> it seems like it would be potentially useful to test this
> in some cases.
> 
> Signed-off-by: Eric Sandeen <sandeen@...hat.com>
  The patch looks good.
Acked-by: Jan Kara <jack@...e.cz>

								Honza

> ---
> 
> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> index 9d5360c..bff5f77 100644
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -1213,6 +1213,23 @@ void writeback_inodes_sb(struct super_block *sb)
>  EXPORT_SYMBOL(writeback_inodes_sb);
>  
>  /**
> + * writeback_inodes_sb_if_idle	-	start writeback if none underway
> + * @sb: the superblock
> + *
> + * Invoke writeback_inodes_sb if no writeback is currently underway.
> + * Returns 1 if writeback was started, 0 if not.
> + */
> +int writeback_inodes_sb_if_idle(struct super_block *sb)
> +{
> +	if (!writeback_in_progress(sb->s_bdi)) {
> +		writeback_inodes_sb(sb);
> +		return 1;
> +	} else
> +		return 0;
> +}
> +EXPORT_SYMBOL(writeback_inodes_sb_if_idle);
> +
> +/**
>   * sync_inodes_sb	-	sync sb inode pages
>   * @sb: the superblock
>   *
> diff --git a/include/linux/writeback.h b/include/linux/writeback.h
> index 66ebddc..dc52482 100644
> --- a/include/linux/writeback.h
> +++ b/include/linux/writeback.h
> @@ -69,6 +69,7 @@ struct writeback_control {
>  struct bdi_writeback;
>  int inode_wait(void *);
>  void writeback_inodes_sb(struct super_block *);
> +int writeback_inodes_sb_if_idle(struct super_block *);
>  void sync_inodes_sb(struct super_block *);
>  void writeback_inodes_wbc(struct writeback_control *wbc);
>  long wb_do_writeback(struct bdi_writeback *wb, int force_wait);
> 
> --
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-- 
Jan Kara <jack@...e.cz>
SuSE CR Labs
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