From: Peter Zijlstra Subject: Re: [patch 1/5] mm: add nofail variants of kmalloc kcalloc and kzalloc Date: Wed, 25 Aug 2010 15:35:42 +0200 Message-ID: <1282743342.2605.3707.camel@laptop> References: <1282656558.2605.2742.camel@laptop> <4C73CA24.3060707@fusionio.com> <20100825112433.GB4453@thunk.org> <1282736132.2605.3563.camel@laptop> <20100825115709.GD4453@thunk.org> <1282740516.2605.3644.camel@laptop> <20100825132417.GQ31488@dastard> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT Cc: Ted Ts'o , David Rientjes , Jens Axboe , Andrew Morton , Neil Brown , Alasdair G Kergon , Chris Mason , Steven Whitehouse , Jan Kara , Frederic Weisbecker , "linux-raid@vger.kernel.org" , "linux-btrfs@vger.kernel.org" , "cluster-devel@redhat.com" , "linux-ext4@vger.kernel.org" , "reiserfs-devel@vger.kernel.org" , "linux-kernel@vger.kernel.org" To: Dave Chinner Return-path: Received: from bombadil.infradead.org ([18.85.46.34]:33070 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753751Ab0HYNgP convert rfc822-to-8bit (ORCPT ); Wed, 25 Aug 2010 09:36:15 -0400 In-Reply-To: <20100825132417.GQ31488@dastard> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Wed, 2010-08-25 at 23:24 +1000, Dave Chinner wrote: > > That is, the guarantee that we will always make progress simply does > not exist in filesystems, so a mempool-like concept seems to me to > be doomed from the start.... While I appreciate that it might be somewhat (a lot) harder for a filesystem to provide that guarantee, I'd be deeply worried about your claim that its impossible. It would render a system without swap very prone to deadlocks. Even with the very tight dirty page accounting we currently have you can fill all your memory with anonymous pages, at which point there's nothing free and you require writeout of dirty pages to succeed.