linux-kernel - Re: [RFC PATCH v5 06/10] ovl: implement overlayfs' ->write

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Date:   Tue, 16 Nov 2021 10:20:25 +0800
From:   Chengguang Xu <cgxu519@...ernel.net>
To:     "Miklos Szeredi" <miklos@...redi.hu>
Cc:     "Jan Kara" <jack@...e.cz>, "Amir Goldstein" <amir73il@...il.com>,
        "linux-fsdevel" <linux-fsdevel@...r.kernel.org>,
        "overlayfs" <linux-unionfs@...r.kernel.org>,
        "linux-kernel" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v5 06/10] ovl: implement overlayfs' ->write_inode
 operation

 ---- 在 星期四, 2021-10-07 21:34:19 Miklos Szeredi <miklos@...redi.hu> 撰写 ----
 > On Thu, 7 Oct 2021 at 15:10, Chengguang Xu <cgxu519@...ernel.net> 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()?
 > 
 > I.e. call write_inode_now() as suggested by Jan.
 > 
 > Also could just call mark_inode_dirty() on the overlay inode
 > regardless of the dirty flags on the upper inode since it shouldn't
 > matter and results in simpler logic.
 > 

Hi Miklos，

Sorry for delayed response for this, I've been busy with another project.

I agree with your suggesion above and further more how about just mark overlay inode dirty
when it has upper inode? This approach will make marking dirtiness simple enough.

Thanks,
Chengguang