Re: [linux-pm] Re: Hibernation considerations

Nigel Cunningham
2007-07-21T22:21:17Z

[-- Attachment #1: Type: text/plain, Size: 2078 bytes --]

Hi.

On Sunday 22 July 2007 04:12:22 Miklos Szeredi wrote:
> > It seems that you could still potentially get a failure to freeze if one
> > FUSE process depends on another, and the one that is frozen second just
> > happens to be waiting on the one that is frozen first when it is frozen.
> > I admit that this situation is unlikely, and perhaps acceptable.
>
> It isn't all that unlikely. There's sshfs for example, that depends
> on a separate ssh process for transport.
>
> Oh, there are also userspace network transports, like tun/tap,
> nfqueue, etc. They could block any network filesystem (not just fuse)
> if frozen first, making the freezer fail.
>
> Hmm, wonder why this isn't affecting people with VPNs? Probably
> network mounts over VPN are rare, and ever rarer to have fs activity
> on them during suspend.
>
> Anyway, I think it's long overdue to stop thinking about how to "fix"
> fuse, and concentrate on fixing the underlying problem instead ;)

That's what I'm seeking to do :)

> > A larger concern is that it seems that freezing FUSE processes at all
> > _will_ generate deadlocks if a non-synchronous or memory-map-supporting
> > filesystem is loopback mounted from a FUSE filesystem. In that case, if
> > you attempt to sync or free memory once FUSE is frozen, you are sure to
> > get a deadlock.
>
> Well, it would deadlock, if
>
> a) memory reclaim was synchronous, or
> b) large part of the memory was used for dirty file data

These are problems in normal operation, aren't they?

> I can't remember if (a) was ever true. And now the dirty ratio is 10%
> by default, so if we go OOM because that 10% can't be reclaimed, there
> is a more serious problem.
>
> Swap over loop over fuse would be problematic, but that won't work for
> some time yet ;)

Hopefully people will wake up to the problems with Fuse and get rid of it
before then :|. Of course I don't really expect that to happen.

Nigel
--
See http://www.tuxonice.net for Howtos, FAQs, mailing
lists, wiki and bugzilla info.

[-- Attachment #2: Type: application/pgp-signature, Size: 189 bytes --]