Re: [PATCH 1/2] writeback: avoid double-writing the inode on a lazytime expiration

Theodore Y. Ts'o
2020-03-25T15:21:42Z

On Wed, Mar 25, 2020 at 02:20:57AM -0700, Christoph Hellwig wrote:
> > spin_unlock(&inode->i_lock);
> >
> > - if (dirty & I_DIRTY_TIME)
> > - mark_inode_dirty_sync(inode);
> > + /* This was a lazytime expiration; we need to tell the file system */
> > + if (dirty & I_DIRTY_TIME_EXPIRED && inode->i_sb->s_op->dirty_inode)
> > + inode->i_sb->s_op->dirty_inode(inode, I_DIRTY_SYNC);
>
> I think this needs a very clear comment explaining why we don't go
> through __mark_inode_dirty.

I can take the explanation which is in the git commit description and
move it into the comment.

> But as said before I'd rather have a new lazytime_expired operation that
> makes it very clear what is happening. We currenly have 4 file systems
> (ext4, f2fs, ubifs and xfs) that support lazytime, so this won't really
> be a major churn.

Again, I believe patch #2 does what you want; if it doesn't can you
explain why passing I_DIRTY_TIME_EXPIRED to s_op->dirty_inode() isn't
"a new lazytime expired operation that makes very clear what is
happening"?

I separated out patch #1 and patch #2 because patch #1 preserves
current behavior, and patch #2 modifies XFS code, which I don't want
to push Linus without an XFS reviewed-by.

N.b. None of the other file systems required a change for patch #2,
so if you want, we can have the XFS tree carry patch #2, and/or
combine that with whatever other simplifying changes that you want.
Or I can combine patch #1 and patch #2, with an XFS Reviewed-by, and
send it through the ext4 tree.

What's your pleasure?

- Ted