On Wed, Oct 11, 2017 at 10:06:00PM +0200, Jan Kara wrote:
> We return IOMAP_F_NEEDDSYNC flag from ext4_iomap_begin() for a
> synchronous write fault when inode has some uncommitted metadata
> changes. In the fault handler ext4_dax_fault() we then detect this case,
> call vfs_fsync_range() to make sure all metadata is committed, and call
> dax_insert_pfn_mkwrite() to insert page table entry. Note that this will
> also dirty corresponding radix tree entry which is what we want -
> fsync(2) will still provide data integrity guarantees for applications
> not using userspace flushing. And applications using userspace flushing
> can avoid calling fsync(2) and thus avoid the performance overhead.
>
> Signed-off-by: Jan Kara <jack@xxxxxxx>
> ---
> fs/ext4/file.c | 6 +++++-
> fs/ext4/inode.c | 15 +++++++++++++++
> fs/jbd2/journal.c | 17 +++++++++++++++++
> include/linux/jbd2.h | 1 +
> 4 files changed, 38 insertions(+), 1 deletion(-)
<>
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 31db875bc7a1..13a198924a0f 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3394,6 +3394,19 @@ static int ext4_releasepage(struct page *page, gfp_t wait)
> }
>
> #ifdef CONFIG_FS_DAX
> +static bool ext4_inode_datasync_dirty(struct inode *inode)
> +{
> + journal_t *journal = EXT4_SB(inode->i_sb)->s_journal;
> +
> + if (journal)
> + return !jbd2_transaction_committed(journal,
> + EXT4_I(inode)->i_datasync_tid);
> + /* Any metadata buffers to write? */
> + if (!list_empty(&inode->i_mapping->private_list))
> + return true;
> + return inode->i_state & I_DIRTY_DATASYNC;
> +}
I just had 2 quick questions on this:
1) Does ext4 actually use inode->i_mapping->private_list to keep track of
dirty metadata buffers? The comment above ext4_write_end() leads me to
believe that this list is unused?
* ext4 never places buffers on inode->i_mapping->private_list. metadata
* buffers are managed internally.
Or does the above comment only apply to ext4 with a journal?
2) Where is I_DIRTY_DATASYNC set in inode->i_state? I poked around a bit and
couldn't see it.
The rest of the patch looks good to me, and you can add:
Reviewed-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
