From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753110AbZBCKJI (ORCPT ); Tue, 3 Feb 2009 05:09:08 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751941AbZBCKIy (ORCPT ); Tue, 3 Feb 2009 05:08:54 -0500 Received: from smtp.nokia.com ([192.100.122.233]:59273 "EHLO mgw-mx06.nokia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751933AbZBCKIx (ORCPT ); Tue, 3 Feb 2009 05:08:53 -0500 Subject: [BUGFIX take 2] [PATCH] write-back: fix nr_to_write counter From: Artem Bityutskiy Reply-To: dedekind@infradead.org To: torvalds@linux-foundation.org Cc: Andrew Morton , Nick Piggin , Linux Kernel Mailing List , linux-fsdevel Content-Type: text/plain; charset="UTF-8" Date: Tue, 03 Feb 2009 12:08:32 +0200 Message-Id: <1233655712.24809.101.camel@localhost.localdomain> Mime-Version: 1.0 X-Mailer: Evolution 2.24.3 (2.24.3-1.fc10) Content-Transfer-Encoding: 8bit X-OriginalArrivalTime: 03 Feb 2009 10:08:28.0884 (UTC) FILETIME=[5C469940:01C985E7] X-Nokia-AV: Clean Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Artem Bityutskiy Date: Mon, 2 Feb 2009 18:33:49 +0200 Subject: [PATCH] write-back: fix nr_to_write counter Commit 05fe478dd04e02fa230c305ab9b5616669821dd3 introduced some @wbc->nr_to_write breakage. Here is the change from the commit: --- a/mm/page-writeback.c +++ b/mm/page-writeback.c @@ -963,8 +963,10 @@ retry: } } - if (--nr_to_write <= 0) - done = 1; + if (wbc->sync_mode == WB_SYNC_NONE) { + if (--wbc->nr_to_write <= 0) + done = 1; + } if (wbc->nonblocking && bdi_write_congested(bdi)) { wbc->encountered_congestion = 1; done = 1 } It makes the following changes: 1. Decrement wbc->nr_to_write instead of nr_to_write 2. Decrement wbc->nr_to_write _only_ if wbc->sync_mode == WB_SYNC_NONE 3. If synced nr_to_write pages, stop only if if wbc->sync_mode == WB_SYNC_NONE, otherwise keep going. However, according to the commit message, the intention was to only make change 3. Change 1 is a bug. Change 2 does not seem to be necessary, and it breaks UBIFS expectations, so if needed, it should be done separately later. And change 2 does not seem to be documented in the commit message. This patch des the following: 1. Undo changes 1 and 2 2. Add a comment explaining change 3 (it very useful to have comments in _code_, not only in the commit). Signed-off-by: Artem Bityutskiy Acked-by: Nick Piggin Cc: Andrew Morton --- mm/page-writeback.c | 21 +++++++++++++++------ 1 files changed, 15 insertions(+), 6 deletions(-) diff --git a/mm/page-writeback.c b/mm/page-writeback.c index b493db7..13a2b8e 100644 --- a/mm/page-writeback.c +++ b/mm/page-writeback.c @@ -1051,13 +1051,22 @@ continue_unlock: } } - if (wbc->sync_mode == WB_SYNC_NONE) { - wbc->nr_to_write--; - if (wbc->nr_to_write <= 0) { - done = 1; - break; - } + if (nr_to_write > 0) + nr_to_write--; + else if (wbc->sync_mode == WB_SYNC_NONE) { + /* + * We stop writing back only if we are not + * doing integrity sync. In case of integrity + * sync we have to keep going because someone + * may be concurrently dirtying pages, and we + * might have synced a lot of newly appeared + * dirty pages, bud have not synced all of the + * old dirty pages. + */ + done = 1; + break; } + if (wbc->nonblocking && bdi_write_congested(bdi)) { wbc->encountered_congestion = 1; done = 1; -- 1.6.0.6 -- Best regards, Artem Bityutskiy (Битюцкий Артём)