From: Chengguang Xu <cgxu519@mykernel.net>
To: "Amir Goldstein" <amir73il@gmail.com>
Cc: "Jan Kara" <jack@suse.cz>,
"linux-fsdevel" <linux-fsdevel@vger.kernel.org>,
"overlayfs" <linux-unionfs@vger.kernel.org>,
"linux-kernel" <linux-kernel@vger.kernel.org>,
"ronyjin" <ronyjin@tencent.com>,
"charliecgxu" <charliecgxu@tencent.com>,
"Vivek Goyal" <vgoyal@redhat.com>,
"Miklos Szeredi" <miklos@szeredi.hu>
Subject: Re: [RFC PATCH v5 06/10] ovl: implement overlayfs' ->write_inode operation
Date: Sun, 05 Dec 2021 22:06:43 +0800 [thread overview]
Message-ID: <17d8aeb19ac.f22523af26365.6531629287230366441@mykernel.net> (raw)
In-Reply-To: <CAOQ4uxiEjGms-sKhrVDtDHSEk97Wku5oPxnmy4vVB=6yRE_Hdg@mail.gmail.com>
---- 在 星期四, 2021-12-02 06:47:25 Amir Goldstein <amir73il@gmail.com> 撰写 ----
> On Wed, Dec 1, 2021 at 6:24 PM Chengguang Xu <cgxu519@mykernel.net> wrote:
> >
> > ---- 在 星期三, 2021-12-01 21:46:10 Jan Kara <jack@suse.cz> 撰写 ----
> > > On Wed 01-12-21 09:19:17, Amir Goldstein wrote:
> > > > On Wed, Dec 1, 2021 at 8:31 AM Chengguang Xu <cgxu519@mykernel.net> wrote:
> > > > > So the final solution to handle all the concerns looks like accurately
> > > > > mark overlay inode diry on modification and re-mark dirty only for
> > > > > mmaped file in ->write_inode().
> > > > >
> > > > > Hi Miklos, Jan
> > > > >
> > > > > Will you agree with new proposal above?
> > > > >
> > > >
> > > > Maybe you can still pull off a simpler version by remarking dirty only
> > > > writably mmapped upper AND inode_is_open_for_write(upper)?
> > >
> > > Well, if inode is writeably mapped, it must be also open for write, doesn't
> > > it? The VMA of the mapping will hold file open. So remarking overlay inode
> > > dirty during writeback while inode_is_open_for_write(upper) looks like
> > > reasonably easy and presumably there won't be that many inodes open for
> > > writing for this to become big overhead?
>
> I think it should be ok and a good tradeoff of complexity vs. performance.
IMO, mark dirtiness on write is relatively simple, so I think we can mark the
overlayfs inode dirty during real write behavior and only remark writable mmap
unconditionally in ->write_inode().
>
> > >
> > > > If I am not mistaken, if you always mark overlay inode dirty on ovl_flush()
> > > > of FMODE_WRITE file, there is nothing that can make upper inode dirty
> > > > after last close (if upper is not mmaped), so one more inode sync should
> > > > be enough. No?
> > >
> > > But we still need to catch other dirtying events like timestamp updates,
> > > truncate(2) etc. to mark overlay inode dirty. Not sure how reliably that
> > > can be done...
> > >
>
> Oh yeh, we have those as well :)
> All those cases should be covered by ovl_copyattr() that updates the
> ovl inode ctime/mtime, so always dirty in ovl_copyattr() should be good.
Currently ovl_copyattr() does not cover all the cases, so I think we still need to carefully
check all the places of calling mnt_want_write().
Thanks,
Chengguang
> I *think* the only case of ovl_copyattr() that should not dirty is in
> ovl_inode_init(), so need some special helper there.
>
> >
> > To be honest I even don't fully understand what's the ->flush() logic in overlayfs.
> > Why should we open new underlying file when calling ->flush()?
> > Is it still correct in the case of opening lower layer first then copy-uped case?
> >
>
> The semantics of flush() are far from being uniform across filesystems.
> most local filesystems do nothing on close.
> most network fs only flush dirty data when a writer closes a file
> but not when a reader closes a file.
> It is hard to imagine that applications rely on flush-on-close of
> rdonly fd behavior and I agree that flushing only if original fd was upper
> makes more sense, so I am not sure if it is really essential for
> overlayfs to open an upper rdonly fd just to do whatever the upper fs
> would have done on close of rdonly fd, but maybe there is no good
> reason to change this behavior either.
>
> Thanks,
> Amir.
>
next prev parent reply other threads:[~2021-12-05 14:08 UTC|newest]
Thread overview: 61+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-23 13:08 [RFC PATCH v5 00/10] implement containerized syncfs for overlayfs Chengguang Xu
2021-09-23 13:08 ` [RFC PATCH v5 01/10] ovl: setup overlayfs' private bdi Chengguang Xu
2021-09-23 13:08 ` [RFC PATCH v5 02/10] ovl: implement ->writepages operation Chengguang Xu
2021-09-23 13:08 ` [RFC PATCH v5 03/10] ovl: implement overlayfs' ->evict_inode operation Chengguang Xu
2021-10-06 15:33 ` Miklos Szeredi
2021-10-07 6:08 ` Chengguang Xu
2021-10-07 7:43 ` Miklos Szeredi
2021-09-23 13:08 ` [RFC PATCH v5 04/10] ovl: mark overlayfs' inode dirty on modification Chengguang Xu
2021-10-07 18:43 ` Miklos Szeredi
2021-09-23 13:08 ` [RFC PATCH v5 05/10] ovl: mark overlayfs' inode dirty on shared mmap Chengguang Xu
2021-09-23 13:08 ` [RFC PATCH v5 06/10] ovl: implement overlayfs' ->write_inode operation Chengguang Xu
2021-10-07 9:01 ` Jan Kara
2021-10-07 12:26 ` Chengguang Xu
2021-10-07 14:41 ` Jan Kara
2021-10-07 14:54 ` Chengguang Xu
2021-10-07 9:23 ` Miklos Szeredi
2021-10-07 12:28 ` Chengguang Xu
2021-10-07 12:45 ` Miklos Szeredi
2021-10-07 13:09 ` Chengguang Xu
2021-10-07 13:34 ` Miklos Szeredi
2021-10-07 14:46 ` Jan Kara
2021-10-07 14:53 ` Chengguang Xu
2021-10-07 18:51 ` Miklos Szeredi
2021-10-08 13:13 ` Jan Kara
2021-11-16 2:20 ` Chengguang Xu
2021-11-16 12:35 ` Miklos Szeredi
2021-11-17 6:11 ` Chengguang Xu
2021-11-18 6:32 ` Chengguang Xu
2021-11-18 11:23 ` Jan Kara
2021-11-18 12:02 ` Chengguang Xu
2021-11-18 16:43 ` Jan Kara
2021-11-19 6:12 ` Chengguang Xu
2021-11-30 11:22 ` Jan Kara
2021-11-30 16:09 ` Chengguang Xu
2021-11-30 19:04 ` Amir Goldstein
2021-12-01 2:37 ` Chengguang Xu
2021-12-01 6:31 ` Chengguang Xu
2021-12-01 7:19 ` Amir Goldstein
2021-12-01 13:46 ` Jan Kara
2021-12-01 14:59 ` Chengguang Xu
2021-12-01 16:24 ` Chengguang Xu
2021-12-01 22:47 ` Amir Goldstein
2021-12-01 23:23 ` ovl_flush() behavior Amir Goldstein
2021-12-02 2:11 ` Chengguang Xu
2021-12-02 15:20 ` Vivek Goyal
2021-12-02 15:59 ` Amir Goldstein
2021-12-02 22:00 ` Vivek Goyal
2021-12-02 15:14 ` Vivek Goyal
2021-12-05 14:06 ` Chengguang Xu [this message]
2021-12-07 5:33 ` [RFC PATCH v5 06/10] ovl: implement overlayfs' ->write_inode operation Amir Goldstein
2022-02-05 16:09 ` Chengguang Xu
2022-02-05 16:23 ` Amir Goldstein
2021-09-23 13:08 ` [RFC PATCH v5 07/10] ovl: cache dirty overlayfs' inode Chengguang Xu
2021-10-07 11:09 ` Miklos Szeredi
2021-10-07 12:04 ` Chengguang Xu
2021-10-07 12:27 ` Miklos Szeredi
2021-09-23 13:08 ` [RFC PATCH v5 08/10] fs: export wait_sb_inodes() Chengguang Xu
2021-09-23 13:08 ` [RFC PATCH v5 09/10] fs: introduce new helper sync_fs_and_blockdev() Chengguang Xu
2021-10-19 7:15 ` Amir Goldstein
2021-11-15 11:39 ` Chengguang Xu
2021-09-23 13:08 ` [RFC PATCH v5 10/10] ovl: implement containerized syncfs for overlayfs Chengguang Xu
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