[Ocfs2-devel] [PATCH 1/2] ocfs2: Flush drive's caches on fdatasync

[Tao Ma]

Hi Jan,

On 07/29/2010 08:00 PM, Jan Kara wrote:
> We have to issue a cache flush during fdatasync even if inode doesn't have
> I_DIRTY_DATASYNC set because we still have to get written *data* to disk to
> observe fdatasync() guarantees.
I am fine with the patch from the code's perspective.

But I just noticed the discussion in fsdevel with the subject "relaxed 
barrier semantics", so with barrier there will be a massive slowdowns 
according to Christoph. And as ocfs2 is mainly used with some SAN, I 
guess in most cases the storage will have a battery backed cache, so we 
may not need this?

Sunil, Joel and Mark, Did you have any user data that most of the ocfs2 
system is used on or can we start a survey in ocfs2-users?

Regards,
Tao

> Signed-off-by: Jan Kara<jack at suse.cz>
> ---
>   fs/ocfs2/file.c |   10 +++++++++-
>   1 files changed, 9 insertions(+), 1 deletions(-)
>
> diff --git a/fs/ocfs2/file.c b/fs/ocfs2/file.c
> index 2b10b36..5659d85 100644
> --- a/fs/ocfs2/file.c
> +++ b/fs/ocfs2/file.c
> @@ -36,6 +36,7 @@
>   #include<linux/writeback.h>
>   #include<linux/falloc.h>
>   #include<linux/quotaops.h>
> +#include<linux/blkdev.h>
>
>   #define MLOG_MASK_PREFIX ML_INODE
>   #include<cluster/masklog.h>
> @@ -190,8 +191,15 @@ static int ocfs2_sync_file(struct file *file, int datasync)
>   	if (err)
>   		goto bail;
>
> -	if (datasync&&  !(inode->i_state&  I_DIRTY_DATASYNC))
> +	if (datasync&&  !(inode->i_state&  I_DIRTY_DATASYNC)) {
> +		/*
> +		 * Although inode doesn't need writing, we still have to flush
> +		 * drive's caches to get data to the platter
> +		 */
> +		blkdev_issue_flush(inode->i_sb->s_bdev, GFP_KERNEL, NULL,
> +				   BLKDEV_IFL_WAIT);
>   		goto bail;
> +	}
>
>   	journal = osb->journal->j_journal;
>   	err = jbd2_journal_force_commit(journal);