On Fri 16-10-20 15:09:38, Chengguang Xu wrote:
> ---- 在 星期四, 2020-10-15 12:57:41 Al Viro <viro@xxxxxxxxxxxxxxxxxx> 撰写 ----
> > On Thu, Oct 15, 2020 at 11:42:51AM +0800, Chengguang Xu wrote:
> > > ---- 在 星期四, 2020-10-15 11:25:01 Al Viro <viro@xxxxxxxxxxxxxxxxxx> 撰写 ----
> > > > On Sat, Oct 10, 2020 at 10:23:51PM +0800, Chengguang Xu wrote:
> > > > > Currently there is no notification api for kernel about modification
> > > > > of vfs inode, in some use cases like overlayfs, this kind of notification
> > > > > will be very helpful to implement containerized syncfs functionality.
> > > > > As the first attempt, we introduce marking inode dirty notification so that
> > > > > overlay's inode could mark itself dirty as well and then only sync dirty
> > > > > overlay inode while syncfs.
> > > >
> > > > Who's responsible for removing the crap from notifier chain? And how does
> > > > that affect the lifetime of inode?
> > >
> > > In this case, overlayfs unregisters call back from the notifier chain of upper inode
> > > when evicting it's own inode. It will not affect the lifetime of upper inode because
> > > overlayfs inode holds a reference of upper inode that means upper inode will not be
> > > evicted while overlayfs inode is still alive.
> >
> > Let me see if I've got it right:
> > * your chain contains 1 (for upper inodes) or 0 (everything else, i.e. the
> > vast majority of inodes) recepients
> > * recepient pins the inode for as long as the recepient exists
> >
> > That looks like a massive overkill, especially since all you are propagating is
> > dirtying the suckers. All you really need is one bit in your inode + hash table
> > indexed by the address of struct inode (well, middle bits thereof, as usual).
> > With entries embedded into overlayfs-private part of overlayfs inode. And callback
> > to be called stored in that entry...
> >
>
> Hi AI, Jack, Amir
>
> Based on your feedback, I would to change the inode dirty notification
> something like below, is it acceptable?
>
>
> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> index 1492271..48473d9 100644
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -2249,6 +2249,14 @@ void __mark_inode_dirty(struct inode *inode, int flags)
>
> trace_writeback_mark_inode_dirty(inode, flags);
>
> + if (inode->state & I_OVL_INUSE) {
> + struct inode *ovl_inode;
> +
> + ovl_inode = ilookup5(NULL, (unsigned long)inode, ovl_inode_test, inode);
I don't think this will work - superblock pointer is part of the hash value
inode is hashed with so without proper sb pointer you won't find proper
hash chain.
Honza
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
