> 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@xxxxxxxxxx>
The patch looks good.
Acked-by: Jan Kara <jack@xxxxxxx>
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@xxxxxxx>
SuSE CR Labs
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