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SubjectRe: [linux-pm] Freezer: Don't count threads waiting for frozen filesystems.

> > > > I don't know. There are other interfaces too, like sysfs attributes,
> > > > that would have to be handled specially. On the whole, the freezer
> > > > seems much, much simpler.
> > >
> > > OK, then non-device files on "regular" filesystems.
> >
> > Would you like to write a first-pass patch? I don't think it will
> > work.
> If somebody doesn't beat me to it, I'll do that (first implemented
> with a global rw-sem).

> > Doing that seems like a lot of work, just as modifying every driver
> > does. Changing a few kernel entry points is simpler, but I'm pretty
> > sure it won't work. For instance, tasks can block arbitrarily long on
> > read calls (waiting for data to arrive); you can't allow such things to
> > prevent the system from suspending.
> But we already do: either
> a) it's in interruptible sleep (I/O on sockets, pipes, etc), and
> freezing simply interrupts it, or
> b) it's in uninterruptible sleep and suspend will wait it out (or
> time out).
> In the new scheme we could retain that part of the freezer: interrupt
> all tasks which are inside the critical region and wait for them to
> exit the critical region.
> To put it in another way: it's still the freezer, it does all the same
> things as the old freezer, except that the condition for freezing is
> not that the task is out of the kernel, rather that it's out of the
> disable_supend - enable_suspend region. As such it's not a big change
> to the whole suspend system, and so there shouldn't be anything big
> going wrong there.

Disadvantage is it will add overhead to regular syscalls, at least
initialy. That's why I implemented freezer initialy...

Of course, suspend is more important than it was back then, and
disadvantages of freezer are now well known, so maybe a little
overhead in exchange of cleaner design is worth it...?
(cesky, pictures)

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