Re: [RFC PATCH v5 06/10] ovl: implement overlayfs' ->write_inode operation

[Jan Kara]

On Thu 07-10-21 15:34:19, Miklos Szeredi wrote:
> On Thu, 7 Oct 2021 at 15:10, Chengguang Xu <cgxu519@xxxxxxxxxxxx> wrote:
> >  > However that wasn't what I was asking about.  AFAICS ->write_inode()
> >  > won't start write back for dirty pages.   Maybe I'm missing something,
> >  > but there it looks as if nothing will actually trigger writeback for
> >  > dirty pages in upper inode.
> >  >
> >
> > Actually, page writeback on upper inode will be triggered by overlayfs ->writepages and
> > overlayfs' ->writepages will be called by vfs writeback function (i.e writeback_sb_inodes).
> 
> Right.
> 
> But wouldn't it be simpler to do this from ->write_inode()?

You could but then you'd have to make sure you have I_DIRTY_SYNC always set
when I_DIRTY_PAGES is set on the upper inode so that your ->write_inode()
callback gets called. Overall I agree the logic would be probably simpler.

								Honza
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR