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Date:   Thu, 7 Oct 2021 16:46:46 +0200
From:   Jan Kara <jack@suse.cz>
To:     Miklos Szeredi <miklos@szeredi.hu>
Cc:     Chengguang Xu <cgxu519@mykernel.net>, Jan Kara <jack@suse.cz>,
        Amir Goldstein <amir73il@gmail.com>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        overlayfs <linux-unionfs@vger.kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH v5 06/10] ovl: implement overlayfs' ->write_inode
 operation
Message-ID: <20211007144646.GL12712@quack2.suse.cz>
References: <20210923130814.140814-1-cgxu519@mykernel.net>
 <20210923130814.140814-7-cgxu519@mykernel.net>
 <CAJfpeguqj2vst4Zj5EovSktJkXiDSCSWY=X12X0Yrz4M8gPRmQ@mail.gmail.com>
 <17c5aba1fef.c5c03d5825886.6577730832510234905@mykernel.net>
 <CAJfpegtr1NkOiY9YWd1meU1yiD-LFX-aB55UVJs94FrX0VNEJQ@mail.gmail.com>
 <17c5adfe5ea.12f1be94625921.4478415437452327206@mykernel.net>
 <CAJfpegt4jZpSCXGFk2ieqUXVm3m=ng7QtSzZp2bXVs07bfrbXg@mail.gmail.com>
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On Thu 07-10-21 15:34:19, Miklos Szeredi wrote:
> On Thu, 7 Oct 2021 at 15:10, Chengguang Xu <cgxu519@mykernel.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()?

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@suse.com>
SUSE Labs, CR