From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754779Ab1FBVWc (ORCPT ); Thu, 2 Jun 2011 17:22:32 -0400 Received: from merlin.infradead.org ([205.233.59.134]:59528 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752381Ab1FBVWa (ORCPT ); Thu, 2 Jun 2011 17:22:30 -0400 Subject: Re: bdi_min_ratio never shrinks, ultimately preventing valid setting of min_ratio From: Peter Zijlstra To: lkml@pengaru.com Cc: linux-kernel@vger.kernel.org, Wu Fengguang , miklos In-Reply-To: <20110602183244.GB5753@shells.gnugeneration.com> References: <20110601002854.GV5753@shells.gnugeneration.com> <1307015011.2497.633.camel@laptop> <20110602183244.GB5753@shells.gnugeneration.com> Content-Type: text/plain; charset="UTF-8" Date: Thu, 02 Jun 2011 23:25:58 +0200 Message-ID: <1307049958.2497.726.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2011-06-02 at 13:32 -0500, lkml@pengaru.com wrote: > > > There is no place in this listing where the value is decremented by the > > > respective bdi's min_ratio when a bdi is torn down. > > > > There is, adding a negative number is equal to a subtraction. > > > > min_ratio -= bdi->min_ratio; > > if (bdi_min_ratio + min_ratio < 100) { > > bdi_min_ratio += min_ratio; > > bdi->min_ratio += min_ratio; > > } > > > > is the relevant piece, note that bdi->min_ratio is the current setting, > > this makes min_ratio the difference between the new and old setting, and > > adding this to both bdi_min_ratio (the global sum) and bdi->min_ratio > > dtrt regardless if the new value is larger or smaller than the old > > value. > > This accounts for the repeated setting of min_ratio on the same bdi. But > does bdi_set_min_ratio() get entered with a min_ratio of 0 on bdi removal? > If not, we leak the non-zero min_ratio of a removed bdi. That does not appear to be the case, good catch. Would you be bitten by that particular scenario? If so, does the below cure things for you? --- mm/backing-dev.c | 1 + 1 files changed, 1 insertions(+), 0 deletions(-) diff --git a/mm/backing-dev.c b/mm/backing-dev.c index f032e6e..e56fe35 100644 --- a/mm/backing-dev.c +++ b/mm/backing-dev.c @@ -606,6 +606,7 @@ static void bdi_prune_sb(struct backing_dev_info *bdi) void bdi_unregister(struct backing_dev_info *bdi) { if (bdi->dev) { + bdi_set_min_ratio(bdi, 0); trace_writeback_bdi_unregister(bdi); bdi_prune_sb(bdi); del_timer_sync(&bdi->wb.wakeup_timer);