Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754049AbYJ1XE2 (ORCPT ); Tue, 28 Oct 2008 19:04:28 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753245AbYJ1XET (ORCPT ); Tue, 28 Oct 2008 19:04:19 -0400 Received: from mail.crca.org.au ([67.207.131.56]:49890 "EHLO crca.org.au" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753215AbYJ1XES (ORCPT ); Tue, 28 Oct 2008 19:04:18 -0400 X-Bogosity: Ham, spamicity=0.000000 Subject: Re: [linux-pm] Freezer: Don't count threads waiting for frozen filesystems. From: Nigel Cunningham To: Miklos Szeredi Cc: linux-pm@lists.linux-foundation.org, linux-kernel@vger.kernel.org In-Reply-To: References: <1224886068.6478.21.camel@nigel-laptop> <1225106427.26724.5.camel@nigel-laptop> <200810271237.40049.rjw@sisk.pl> <1225107607.26724.9.camel@nigel-laptop> <1225141168.26724.23.camel@nigel-laptop> <1225145607.26724.54.camel@nigel-laptop> Content-Type: text/plain Organization: Christian Reformed Churches of Australia Date: Wed, 29 Oct 2008 10:04:14 +1100 Message-Id: <1225235054.9661.37.camel@nigel-laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.22.3.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2603 Lines: 60 Hi again. On Tue, 2008-10-28 at 21:25 +0100, Miklos Szeredi wrote: > On Tue, 28 Oct 2008, Nigel Cunningham wrote: > > The answer is to freeze the fuse filesystems first, stopping new > > requests (freezing the processes making them) before they are passed on > > to userspace and allowing existing requests to complete or freeze. Once > > that is done, the userspace fuse processes will be idle, at least as far > > as fuse activity is concerned. After fuse activity is stopped, userspace > > can be frozen without worrying about what processes are fuse and what > > aren't. This is what my patch implements so far. > > OK. > > > To deal with requests that are already in progress, I'd suggest three > > possibilities, in the order I think they should be preferred. > > > > 1) Use wait_event_freezeable[_timeout] in fuse code. Probably preferable > > to #2, but I thought of it later :) > > > > 2) Use freezer_do_not_count as part of FUSE_MIGHT_FREEZE (resetting > > before exiting the callers, of course). If the request doesn't complete > > during the freezing period, it must be because the userspace thread was > > already frozen. If the request does complete, we're counted again during > > the normal freezing of userspace that follows the freezing of > > filesystems. > > > > 3) Adding a means to check whether processes being frozen are fuse > > requests. The code could then wait for fc->num_waiting - (say) > > fc->num_frozen == 0. > > Yup, these fix the freezing of tasks which have outstanding fuse > requests. > > However it does not fix the freezing of tasks which are waiting for > VFS locks (i.e. inode->i_mutex) held by the outstanding fuse requests. > This is the tricky part... Okay. Looking back on our conversation brought me back to this message, which I think needs another reply. If we take the strategy of holding new requests and allowing existing ones to complete, then am I right in thinking that we only need to worry about where inode->i_mutex is taken in fs/fuse/file.c (I don't see it taken in other fs/fuse/*.c files). If that's correct, dealing with that issue looks relatively straight forward: we need some more FUSE_MIGHT_FREEZE calls for those functions, and something done to the vfs_check_frozen call - I'm a bit confused by that - inode->i_sb will refer to the fuse filesystem, won't it? Regards, Nigel -- 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/