From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751721AbaAXXF3 (ORCPT ); Fri, 24 Jan 2014 18:05:29 -0500 Received: from mx1.redhat.com ([209.132.183.28]:29594 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751087AbaAXXF0 (ORCPT ); Fri, 24 Jan 2014 18:05:26 -0500 Message-ID: <52E2F1A5.7010907@redhat.com> Date: Fri, 24 Jan 2014 18:05:09 -0500 From: Rik van Riel User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.2.0 MIME-Version: 1.0 To: Johannes Weiner , Andrew Morton CC: Tejun Heo , Mel Gorman , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [patch 1/2] mm: page-writeback: fix dirty_balance_reserve subtraction from dirtyable memory References: <1390600984-13925-1-git-send-email-hannes@cmpxchg.org> <1390600984-13925-2-git-send-email-hannes@cmpxchg.org> In-Reply-To: <1390600984-13925-2-git-send-email-hannes@cmpxchg.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/24/2014 05:03 PM, Johannes Weiner wrote: > The dirty_balance_reserve is an approximation of the fraction of free > pages that the page allocator does not make available for page cache > allocations. As a result, it has to be taken into account when > calculating the amount of "dirtyable memory", the baseline to which > dirty_background_ratio and dirty_ratio are applied. > > However, currently the reserve is subtracted from the sum of free and > reclaimable pages, which is non-sensical and leads to erroneous > results when the system is dominated by unreclaimable pages and the > dirty_balance_reserve is bigger than free+reclaimable. In that case, > at least the already allocated cache should be considered dirtyable. > > Fix the calculation by subtracting the reserve from the amount of free > pages, then adding the reclaimable pages on top. > > Signed-off-by: Johannes Weiner Reviewed-by: Rik van Riel -- All rights reversed