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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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