From: Pavel Machek Subject: Re: [PATCH 3/3] Add timeout feature Date: Wed, 9 Jul 2008 01:20:31 +0200 Message-ID: <20080708232031.GE18195@elf.ucw.cz> References: <20080630212450t-sato@mail.jp.nec.com> <20080701081026.GB16691@infradead.org> <20080707110730.GG5643@ucw.cz> <20080708231026.GP11558@disturbed> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii To: Christoph Hellwig , Takashi Sato , akpm@linux-foundation.org, viro@ZenIV.linux.org.uk, "linux-ext4@vger.kernel.org" Received: from gprs189-60.eurotel.cz ([160.218.189.60]:33513 "EHLO gprs189-60.eurotel.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759257AbYGHXTi (ORCPT ); Tue, 8 Jul 2008 19:19:38 -0400 Content-Disposition: inline In-Reply-To: <20080708231026.GP11558@disturbed> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Wed 2008-07-09 09:10:27, Dave Chinner wrote: > On Mon, Jul 07, 2008 at 01:07:31PM +0200, Pavel Machek wrote: > > Hi! > > > > > I still disagree with this whole patch. There is not reason to let > > > the freeze request timeout - an auto-unfreezing will only confuse the > > > hell out of the caller. The only reason where the current XFS freeze > > > call can hang and this would be theoretically useful is when the > > > > What happens when someone dirties so much data that vm swaps out > > whatever process that frozen the filesystem? > > a) you can't dirty a frozen filesystem - by definition a frozen > filesystem is a *clean filesystem* and *cannot be dirtied*. Can you stop me? mmap("/some/huge_file", MAP_SHARED); then write to memory mapping? > b) Swap doesn't write through the filesystem > c) you can still read from a frozen filesystem to page your > executable?? in. atime modification should mean dirty data, right? And dirty data mean memory pressure, right? > d) if dirtying another unfrozen filesystem swaps out your ~~~~~~~ > application so it can't run, then there's a major VM bug. > Regardless, until the app completes it is relying on the > filesystem being frozen, so it better remain frozen.... Agreed. With emphasis on "another". > > I though that was why the timeout was there... > > Not that I know of. Ok, lets see how you deal with mmap. Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html