Re: [PATCH] [5/48] Suspend2 2.1.9.8 for 2.6.12: 350-workthreads.patch

Pavel Machek
2005-07-12T11:26:55Z

Hi!

> > > > > > Again, why do you think you need this?
> > > > >
> > > > > 1. If something should be wrong with the freezer, it forms part of a
> > > > > safety net that stops your data on disk being trashed.
> > > >
> > > > > 2. Separating out threads doing syncing from threads submitting I/O
> > > > > makes the refrigerator much more reliable, even under extreme load.
> > > >
> > > > This seems to be red herring. Sometimes sync took way too long (like
> > > > hours) with older kernels and reiserfs, but I believe that has been
> > > > fixed. If not, we need to fix it, anyway; no need to work around it in
> > > > suspend2.
> > >
> > > Are you considering races such as the case where one process is
> > > submitting I/O (say dd) while another is trying to sync? Even if sync
> > > does return sooner (presumably because it only syncs writes submitted
> > > before the sync), there will still be dirty data after the sync
> > > completes. And if we start another sync thread, it will suffer the same
> > > problem. The only solution is to stop I/O being submitted, then sync.
> > > But having stopped I/O being submitted, we need to still have the
> > > threads the process the I/O (possibly userspace ones) unfrozen. Hence we
> > > need to differentiate 'syncthreads'.
> >
> > OTOH: this is only critical for "niceness", not for
> > correctness. Calling sync() before suspend is simply nice thing to do,
> > but it is not required in any way. If someone is doing long dd, tough,
> > they are going to loose some data if wakeup fails. It is no worse than
> > sudden poweroff.
>
> How can you say it's only required for niceness one minute, then admit
> it might result in data loss the next?

It will result in data loss *if resume fails*. But failing resume
*always* causes data in running programs to be lost, so I do not see
that as a problem.
Pavel
--
teflon -- maybe it is a trademark, but it should not be.