Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753511AbYKOQ7T (ORCPT ); Sat, 15 Nov 2008 11:59:19 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751345AbYKOQ7L (ORCPT ); Sat, 15 Nov 2008 11:59:11 -0500 Received: from gprs189-60.eurotel.cz ([160.218.189.60]:50551 "EHLO UNKNOWN" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751476AbYKOQ7K (ORCPT ); Sat, 15 Nov 2008 11:59:10 -0500 Date: Sat, 15 Nov 2008 17:58:51 +0100 From: Pavel Machek To: Miklos Szeredi Cc: stern@rowland.harvard.edu, rjw@sisk.pl, linux-kernel@vger.kernel.org, ncunningham@crca.org.au, linux-pm@lists.linux-foundation.org Subject: Re: [linux-pm] Freezer: Don't count threads waiting for frozen filesystems. Message-ID: <20081115165851.GA1523@ucw.cz> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2278 Lines: 56 Hi! > > > > 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). Cool! l > > 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...? Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/