From mboxrd@z Thu Jan 1 00:00:00 1970 From: Artem Bityutskiy Subject: [BUGFIX take 4] [PATCH] write-back: fix nr_to_write counter Date: Tue, 03 Feb 2009 17:44:59 +0200 Message-ID: <1233675899.5138.19.camel@localhost.localdomain> References: <1233655712.24809.101.camel@localhost.localdomain> <1233668461.30906.4.camel@norville.austin.ibm.com> <1233672349.5138.12.camel@localhost.localdomain> <49885ABD.2010600@hp.com> Reply-To: dedekind@infradead.org Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Andrew Morton , Nick Piggin , Linux Kernel Mailing List , linux-fsdevel To: torvalds Return-path: In-Reply-To: <49885ABD.2010600@hp.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org [Fix spelling, pointed to by jim owens] =46rom: 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 <=3D 0) > done =3D 1; > if (wbc->sync_mode =3D=3D WB_SYNC_NONE) { > if (--wbc->nr_to_write <=3D 0) > done =3D 1; > } > if (wbc->nonblocking && bdi_write_congested(bdi= )) { > wbc->encountered_congestion =3D 1; > done =3D 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 =3D=3D WB_SYNC_N= ONE 3. If synced nr_to_write pages, stop only if if wbc->sync_mode =3D=3D 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 does the following: 1. Undo changes 1 and 2 2. Add a comment explaining change 3 (it very useful to have comments i= n _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..dc32dae 100644 --- a/mm/page-writeback.c +++ b/mm/page-writeback.c @@ -1051,13 +1051,22 @@ continue_unlock: } } =20 - if (wbc->sync_mode =3D=3D WB_SYNC_NONE) { - wbc->nr_to_write--; - if (wbc->nr_to_write <=3D 0) { - done =3D 1; - break; - } + if (nr_to_write > 0) + nr_to_write--; + else if (wbc->sync_mode =3D=3D 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, but have not synced all of the + * old dirty pages. + */ + done =3D 1; + break; } + if (wbc->nonblocking && bdi_write_congested(bdi)) { wbc->encountered_congestion =3D 1; done =3D 1; --=20 1.6.0.6 --=20 Best regards, Artem Bityutskiy (=D0=91=D0=B8=D1=82=D1=8E=D1=86=D0=BA=D0=B8=D0=B9 =D0=90= =D1=80=D1=82=D1=91=D0=BC)