From: Mel Gorman Subject: Re: [patch 1/5] mm: exclude reserved pages from dirtyable memory Date: Mon, 3 Oct 2011 12:22:05 +0100 Message-ID: <20111003112205.GA5011@suse.de> References: <1317367044-475-1-git-send-email-jweiner@redhat.com> <1317367044-475-2-git-send-email-jweiner@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Cc: Andrew Morton , Christoph Hellwig , Dave Chinner , Wu Fengguang , Jan Kara , Rik van Riel , Minchan Kim , Chris Mason , Theodore Ts'o , Andreas Dilger , Shaohua Li , xfs@oss.sgi.com, linux-btrfs@vger.kernel.org, linux-ext4@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org To: Johannes Weiner Return-path: Received: from cantor2.suse.de ([195.135.220.15]:47161 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752592Ab1JCLWM (ORCPT ); Mon, 3 Oct 2011 07:22:12 -0400 Content-Disposition: inline In-Reply-To: <1317367044-475-2-git-send-email-jweiner@redhat.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Fri, Sep 30, 2011 at 09:17:20AM +0200, Johannes Weiner wrote: > The amount of dirtyable pages should not include the full number of > free pages: there is a number of reserved pages that the page > allocator and kswapd always try to keep free. > > The closer (reclaimable pages - dirty pages) is to the number of > reserved pages, the more likely it becomes for reclaim to run into > dirty pages: > > +----------+ --- > | anon | | > +----------+ | > | | | > | | -- dirty limit new -- flusher new > | file | | | > | | | | > | | -- dirty limit old -- flusher old > | | | > +----------+ --- reclaim > | reserved | > +----------+ > | kernel | > +----------+ > > This patch introduces a per-zone dirty reserve that takes both the > lowmem reserve as well as the high watermark of the zone into account, > and a global sum of those per-zone values that is subtracted from the > global amount of dirtyable pages. The lowmem reserve is unavailable > to page cache allocations and kswapd tries to keep the high watermark > free. We don't want to end up in a situation where reclaim has to > clean pages in order to balance zones. > > Not treating reserved pages as dirtyable on a global level is only a > conceptual fix. In reality, dirty pages are not distributed equally > across zones and reclaim runs into dirty pages on a regular basis. > > But it is important to get this right before tackling the problem on a > per-zone level, where the distance between reclaim and the dirty pages > is mostly much smaller in absolute numbers. > > Signed-off-by: Johannes Weiner > Reviewed-by: Rik van Riel Acked-by: Mel Gorman -- Mel Gorman SUSE Labs