From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nick Piggin Subject: Re: [patch][rfc] mm: hold page lock over page_mkwrite Date: Sun, 1 Mar 2009 14:50:57 +0100 Message-ID: <20090301135057.GA26905@wotan.suse.de> References: <20090225093629.GD22785@wotan.suse.de> <20090301081744.GI26138@disturbed> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii To: linux-fsdevel@vger.kernel.org, Linux Memory Management List Return-path: Content-Disposition: inline In-Reply-To: <20090301081744.GI26138@disturbed> Sender: owner-linux-mm@kvack.org List-Id: linux-fsdevel.vger.kernel.org On Sun, Mar 01, 2009 at 07:17:44PM +1100, Dave Chinner wrote: > On Wed, Feb 25, 2009 at 10:36:29AM +0100, Nick Piggin wrote: > > I need this in fsblock because I am working to ensure filesystem metadata > > can be correctly allocated and refcounted. This means that page cleaning > > should not require memory allocation (to be really robust). > > Which, unfortunately, is just a dream for any filesystem that uses > delayed allocation. i.e. they have to walk the free space trees > which may need to be read from disk and therefore require memory > to succeed.... Well it's a dream because probably none of them get it right, but that doesn't mean its impossible. You don't need complete memory allocation up-front to be robust, but having reserves or degraded modes that simply guarantee forward progress is enough. For example, if you need to read/write filesystem metadata to find and allocate free space, then you really only need a page to do all the IO. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org